switch yard erection(2)

FOR INTERNAL CIRCULATION ONLY

user’s manualof

Construction(part two)

Sub-StationsVolume-3

Switchyard Erection

Construction Management

Power Grid Corporation of India Limited(A Government of India Enterprise)

DOCUMENT CODE NO. : CM/SS/SW. ERN/99 SEPT, 1999

CONTENTS

CHAPTER ONE

ELECTRICAL SUBSTATION

PAGE NO.

1.O INTRODUCTION 1

1.1 FUNCTIONS OF A SUB-STATION 2

1.2 VOLTAGE LEVELS IN AC SUBSTATIONS

AND HVDC SUBSTATIONS 3

1.3 FORMS OF SUBSTATIONS 4

1.4 TYPES OF SUBSTATIONS 6

1.5 ESSENTIAL FEATURES OF A SUBSTATION 7

1.5.1 SPECIAL FEATURES 12

1.6 SITE SELECTION 13

ANNEXURE - I

FORMAT FOR COMPARATIVE STATEMENT OF

SITES FOR SUBSTATION 14

1.6.1 LAND ACQUISITION 16

1.6.2 PROVISIONS UNDER THE LAND

ACQUISITION ACT, 1894 FOR SUB-STATIONS 16

1.6.3 LAND ACQUISITION ACT,1894 AS AMENDED

IN 1984 17

ANNEXURE - II

ACTIVITY CHART(TIME FRAME) 18

1.7 SUBSTATION PARTS AND EQUIPMENT

1.8 FUNCTIONS OF SUB-STATION EQUIPMENTS &

ASSOCIATED SYSTEMS

1.9 SUBSTATIN LAYOUTS, BUSBAR SCHEMES

1.10 CONSTRUCTION/ERECTION DRAWINGS

CHAPTER TWO

SWITCHYARD CIVIL WORKS

2.0 INTRODUCTION

2.1 SOIL INVESTIGATION

2.2 LEVELLING

2.3 FOUNDATIONS

2.4 FOUNDATIONS FOR TRANSFORMER & SHUNT

REACTORS

2.5 CABLE TRENCHES IN SWITCHYARD

2.6 CABLE TRENCH COVER SLABS

2.7 ANTI-WEED TREATMENT, MICRO LEVELLING’

GRAVEL FILLING & METAL SPREADING

2.7.1 ANTI-WEED TREATMENT

2.7.2 MICRO LEVELLING

2.7.3 METAL SPREADING IN SWITCHYARD

2.8 DO’S, DON’T’S & SPECIAL PRECAUTIONS

2.9 CHECK FORMAT

CHAPTER THREE

SWITCHYARD EARTHING

3.0 INTRODUCTION3.1 FUNCTIONAL REQUIREMENTS OF EARTHING SYSTEM

3.2 EARTHNG SYSTEM IN SWITCHYARD3.3 STEP AND TOUCH POTENTIAL3.3.1 STEP POTENTIAL3.3.2 TOUCH POTENTIAL3.4 SOIL RESISTIVITY

3.5 EARTHING MATERIAL

3.6 EARTHING CONDUCTOR LAYOUT 45

3.7 EQUIPMENT AND STRUCTURE EARTHING

IN SUBSTATION 45

3.8 JOINTING 48

3.9 MEASUREMENT OF EARTH RESISTANCE 49

3.10 DO'S DON'TS AND SPECIAL PRECAUTIONS 50

3.11 CHECK FORMAT

CHAPTER FOUR

SWITCHYARD STRUCTURES

4.0 INTRODUCTION 54

4.1 STRUCTURE WORKS IN SUBSTATION

SWITCHYARD 54

4.2 RECEIPT OF MATERIAL & INSPECTION 54

4.3 STORAGE 55

4.4 ERECTION 55

4.4.1 ERECTION OF GANTRY & LATTICE STRUCTURES 55

4.4.2 ERECTION OF PIPE STRUCTURE 57

4.3 LIGHTNING MASTS 57

4.4 DO'S, DONT'S AND SPECIAL PRECAUTIONS 58

4.5 CHECK FORMAT 60

CHAPTER FIVE

BUS POST INSULATORS & BUS BARS

5.0 INTRODUCTION 62

5.1 STEPS IN BUSBAR DESIGN 62

5.2 FORMS OF BUSBARS 63

5.2.1 ACSR 63

5.2.2 ALUMINIUM 63

5.3 CONFIGURATION OF BUSBARS IN

OUTDOOR SUBSTATION 64

5.4 RECEIPT AND INSPECTION OF MATERIAL

AT SITE 64

5.5 BUS POST INSULATORS 65

5.5.1 TECHNICAL PARAMETERS OF BUS POST

INSULATORS 66

5.6 ERECTION OF ALUMINIUM BUS BAR 67

5.6.1 BENDING PROCEDURE OF ALUMINIUM TUBE

DURING ERECTION 68

5.6.2 WELDING OF ALUMINIUM TUBE 68

5.7 WELDING PROCEDURE AND WELDER'S

QUALIFICATIONS 69


5.9 CHECK FORMAT 71

CHAPTER SIX

STRINGING IN SWITCHYARD

6.0 INTRODUCTION 78

6.1 PRE-STRINGING CHECKS 78

6.2 STRINGING 79

6.3 T&P AND MATERIALS USED FOR STRINGING 79

6.4 DO’S DONT’S AND SPECIAL PRECAUTIONS 81

6.5 CHECK FORMAT 84

CHAPTER SEVEN

SURGE ARRESTER

7.0 INTRODUCTION 86

7.1 CONVENTIONAL GAPPED LIGHTNING ARRESTER

(VALVE TYPE ARRESTER) 86

7.2 METAL OXIDE LIGHTNING ARRESTERS 87

7.3 PACKING, TRANSPORT, HANDLING AND STORAGE 88

7.4 INSTALLATION 89

7.5 INSTALLATION OF SINGLE UNIT ARRESTER 89

7.6 INSTALLATION OF MULTI-STACK ARRESTER 89

7.7 DO'S, DONT'S & SPECIAL PRECAUTIONS 91

7.8 CHECK FORMAT 92

CHAPTER EIGHT

ISOLATORS

8.0 INTRODUCTION 94

8.1 CONSTRUCTION FEATURES 94

8.1.1 SUPPORT STRUCTURE 95

8.1.2 BASE ASSEMBLY 95

8.1.3 INSULATOR ASSEMBLY 95

8.1.4 MALE AND FEMALE CONTACTS ASSEMBLY 96

8.2. OPERATING MECHANISM 96

8.2.1 GEARED OPERATING MECHANISM 96

8.2.2 MANUAL OPERATING MECHANISM 96

8.2.3 EARTH SWITCH ASSEMBLY 97

8.3 RECEIPT, HANDLING AND STORAGE 97

8.4 ERECTION/INSTALLATIONS 97

8.4.1 STRUCTURES 97

8.4.2 BASE ASSEMBLY 98

8.4.3 INSULATORS 98

8.4.4 CONTACTS ASSEMBLY (MALE AND FEMALE

ASSEMBLY) 99

8.4.5 CONNECTING DISCONNECTOR 100

8.4.6 CONTROLS FOR ELECTRICAL

OPERATING EQUIPMENT 101

8.5 CLOSING OPERATION OF ISOLATOR 101

8.6 TANDEM PIPE ASSEMBLY 102

8.7 EARTH SWITCH ASSEMBLY 102


8.8.1 ADJUSTMENT IN DRIVE/ASSEMBLY ERECTION 104

8.9 CHECK FORMAT 107

CHAPTER NINECURRENT TRANSFORMER

9.0 INTRODUCTION 109


9.2 HERMETIC SEALING 111

9.3 TRANSPORTATION, UNPACKING & INSPECTION 111

9.4 INSTALLATION/ERECTION 112

9.5 DO'S DONT'S & SPECIAL PRECAUTIONS 114


CHAPTER TENCAPACITIVE VOLTAGE TRANSFORMER


10.1 DESCRIPTION & OPERATING PRINCIPLE 117

10.2 PACKING AND TRANSPORTATION 119

10.3 RECEIVING 120

10.4 UNLOADING 120

10.5 STORAGE 121

10.6 INSTALLATION 122

10.7 CONNECTION 122


10.8.1 INSPECTION BEFORE MOUNTING 125

10.8.2 DEFECT/DAMAGE 126

10.8.3 MINOR IRREGULARITIES 127

10.8.4 ERECTION 127


CHAPTER ELEVENPOWER LINE CARRIER COMMUNICATION


11.1 PLC SYSTEM 129

11.2 COUPLING EQUIPMENT 129

11.3 COUPLING EQUIPMENT DESCRIPTION 130


11.5 DATA TRANSMISSION 131

11.6 TELEPROTECTION 131

11.7 CARRIER PANEL 131

11.8 EARTHING 131

11.9 ERECTION OF PLCC AND ASSOCIATED

EQUIPMENT 132

11.9.1 OUTDOOR EQUIPMENTS 132

11.9.2 INDOOR EQUIPMENTS 134

11.10 CONNECTION OF HF CO-AXIAL CABLE 136

11.11 INSTALLATION OF EQUIPMENT AS PER

PLANNED SYSTEM 137

11.12 DEFECTIVE MODULES AND FAULT

RECTIFICATION AT SITE 137

11.13 DO'S, DON'TS AND SPECIAL PRECAUTIONS 139


CHAPTER TWELVECABLES


12.1 RECEIPT, INSPECTION AND STORAGE 144

12.2 CABLE LAYING IN SWITCHYARD 144

12.2.1 CABLE LAYING IN UNDERGROUND

(BURIE TRENCHES) 145

12.2.2 CABLE LAYING IN CABLE TRAYS 145

12.3 CABLE TERMINATION 146



CHAPTER THIRTEENCONTROL AND RELAY PANELS



13.2 SIMPLEX PANEL 156

13.3 DUPLEX PANEL 156

13.4 RECEIPT AND STORAGE AT SITE 156

13.5 ERECTION OF PANELS 157

13.6 MOUNTING ON PANELS 158

13.7 PANEL INTERNAL WIRING AND EQUIPMENTS

IN PANELS 158

13.8 PROVIDING TERMINAL BLOCKS 159

13.9 NAME PLATES AND MARKINGS 160

13.10 PANELS ACCESSORIES 160

13.11 EARTHING 161


13.13 CHECK FORMAT

Chapter-1ELECTRICAL SUBSTATION

_________________________________________________________________________________

CHAPTER ONE

_________________________________________________________________________________

ELECTRICAL SUBSTATIONBack to contents page

1.0 Introduction Back to contents page

An electrical Network comprises of the following systems:

Generating Stations

Transmission Systems

Receiving Stations

Distribution Systems

Load Points

In all these systems, the power flow of electrical energy takes place

through Electrical Substations. An Electrical Substation is an

assemblage of electrical components including busbars, switchgear,

power transformers, auxiliaries, etc. Basically an electrical substation

consists of a number of incoming circuits and outgoing circuits

connected to common busbar system. Busbars are conducting bars to

which a number of incoming or outgoing circuits are connected. Each

circuit has certain electrical components such as circuit-breakers,

isolators, earthing switches, current transformers, voltage transformers,

etc. These components are connected in a definite sequence such that

a circuit can be switched off/on during normal operation by

manual/remote command and also automatically during abnormal

conditions such as short-circuits.

A substation receives electrical power from generating station via

incoming transmission lines and delivers electrical power via the

outgoing transmission lines. Substations are integral parts of a power

system and form important links between the generating stations,

transmission and distribution systems and the load points.

1.1 Functions of a sub-station:Back to contents page

An electricity supply undertaking generally aims at the following:

Supply of required electrical power to all the consumers

continuously at all times.

Maximum possible coverage of the supply network over the given

geographical area.

Maximum security of supply.

Shortest possible fault duration.

Optimum efficiency of plants and the network.

Supply of electrical power within targeted frequency limits.

Supply of electrical power within specified voltage limits.

Supply of electrical energy to the consumers at the lowest cost.

As a result of these objectives, there are various tasks which are

closely associated with the generation, transmission, distribution and

utilisation of the electrical energy. These tasks are performed by

various, manual, semi-automatic and fully automatic devices located in

generating stations and substations.

The tasks associated with a major substation in the transmission

system include the following:

Controlling the exchange of energy

Protection of transmission system

Ensuring steady state and transient stability

Load shedding and prevention of loss of synchronism.

Maintaining the system frequency within targeted limits

Voltage control, reducing the reactive power flow by

compensation of reactive power, tap-changing.

Securing the supply by providing adequate line capacity and

facility for changing the transmission paths.

Data transmission via power line carrier for the purpose of

network monitoring, control and protection.

Determining the energy transfer through transmission lines and

tie-lines.

Fault analysis and pin-pointing the cause and subsequent

improvements.

Securing supply by feeding the network at various points.

All these tasks are performed by the team work of load-control centre

and control rooms of substations. The substations perform several

important tasks and are integral part of the power system.

1.2 Voltage Levels in AC Substations and HVDC Substations Back to contents page

A substation receives power via the incoming transmission lines and delivers

power via the outgoing lines. The substation may have step-up

transformers or step-down transformers. Generally the switchyards at

sending-end of lines have step-up transformers and switchyards at

receiving-end have step-down transformers. The rated voltage level

refers to nominal voltage of 3 phase AC system and is expressed as

r.m.s. value between phases. An AC substation has generally 2 or 3

main voltage levels. The long distance transmission is generally at

extra high voltages such as 132 kV, 220 kV, 400 kV AC The

subtransmission is at medium high voltage such as 33 kV, 11 kV AC.

In a generating station, the generator is directly connected to step-up

transformer and secondary of the step-up transformer is connected to

outdoor EHV switchyard. The switchyard in a generating station

comprises generator transformer, unit auxiliary transformer and several

out-going lines. In addition to the main EHV switchyard, a generating

station has indoor auxiliary switchgear at two or three voltages such as

11 kV, 400 Volts.

The factory substations receive power at distribution voltage such as

11 kV and step it down to 440 volts AC. Larger factories receive power

at 132 kV and have internal distribution at 440 volts AC.

The choice of incoming and outgoing voltages of substations is decided

by the rated voltages and rated power of corresponding lines. Long

distance and high power transmission lines are at higher voltages. The

nominal voltages are selected from the standard values of rated

voltages specified in Indian Standards or relevant national standard.

The standards also specify the following reference values for each

voltage level.

Nominal voltage e.g. 220 kV, 400 kV

Highest system voltage, e.g. 245 kV, 420 kV

Lowest system voltage, e.g. 200 kV, 185 kV.

Table 1: Reference Values of Nominal Voltages in AC and HVDC Substations

AC Substation765 kV, 400 kV, 220 kV, 132 kV, 66 kV, 33 kV, 11 kV

HVDC Substation+400 Kv, +500 kV, +600 kV

Station AuxiliariesAux. AC Supply : 33 kV, 11 kV

400 V, 3 ph., phase to phase

230 V AC single phase

Aux. LVDC : 220 V, 110 V, 48 V DC

1.3 Forms of Substations Back to contents page

For voltage upto 11 kV, the sub-stations are either in the form of indoor

metal clad draw-out type Switchgear or Outdoor Kiosk. In indoor metal

clad switchgear, the required number of factory assembled units are

taken to site and placed in a row. SF6 Gas Insulated Switchgear has

been introduced for medium to high voltages such as 11 kV, 33 kV &

upto 400 kV level.

For voltages of 33 kV and above, outdoor substations are generally

preferred. In outdoor substations, the various equipments are installed

in open.

The indoor and outdoor substations have similar components.

However, configurations, assembly and dimensions of indoor sub-

stations are quite different from those of outdoor substations.

SF6 Gas Insulated Substations (GIS) are preferred for the following

EHV, HV Substations.

Substations in urban areas, industrial areas, mountainous regions

where land is costly and civil works are complex.

Heavily polluted areas such as sea-shores, industrial areas,

thermal power stations etc. Where open terminal substations

experience frequent flashovers.

Maintenance free substations.

Besides the main voltage levels, each substation has auxiliary AC and

DC distribution systems for feeding the various auxiliary systems,

protection systems and control systems. The reference values of

auxiliary voltage are mentioned above in in Table -1.

High voltage DC Transmission systems (HVDC) have following parts at

each end of the HVDC Transmission line.

EHV AC yard which is at 400 kV AC or 220 kV AC

HVDC yard which is at + 400 kV DC or + 500 kV DC etc.

Valve hall, Converter Transmission and AC Filters.

Electrode line, earth electrode.

Bipolar HVDC system has two poles, one of a positive and other

negative polarity with respect to earth. The nominal voltage + 500 kV

refers to voltage of the two DC poles with respect to earth. The

midpoint of converters is earthed through earth electrodes. One HVDC

substation is required at each end of the long HVDC transmission line.In case of Back-to-Back HVDC substation, the long distance HVDC

transmission line is eliminated and such substation has the following

parts:

AC Switchyard of one grid.

AC Switchyard of other grid.

Back-to-back converter transformers and valves.

Such substations are used for asynchronous links between two AC

systems for interconnection. The frequency fluctuations on one AC side

are not reflected on the other AC side and the power can be

transferred in either directions by adjusting the characteristics of the

converter valves. Power can be exchanged rapidly and accurately in a

controlled way.

1.4 Types of Substations Back to contents page

The substations can be classified in several ways including the

following:

i) Classification based on voltage levels e.g.:

AC Substation: EHV, HV, MV, LV; HVDC substation

ii) Classification-outdoor or indoor.

Outdoor substation is under open sky. Indoor substation is

inside a building.

iii) Classification based on configuration, e.g.:

a) Conventional air insulated outdoor substation or

b) SF6 Gas Insulated Substation (GIS)

c) Composite substations having combination of the above two.

iv) Classification based on application.

a) Distribution substation

b) Switchyard in Generating Station

c) Switching substation (without power transformers)

d) Sending-end substation

e) Receiving substation

f) Factory substation

g) Compensating substation e.g. having static var compensation etc.

h) Load substation, e.g. arc-furnace substation.

Table-2 given below gives the Main Data about a typical

400/230 kV AC Substation.

Table 2: Main Data of a Typical 400/220 kV Outdoor AC Substation

Operating Voltage 400 kV 220 kVRated current 2000/3150 A 2000AMaximum Short-circuit current in busbar 40 kA 40 kAMinimum phase to phase clearance 5.75 m 2.5 mMinimum phase to earth clearance 3.50 m 2.1 mNumber of horizontal levels of tubular

busbars/flexible busbars

2 2

Height of tubular busbars of first level above

ground

8 m 5.5 m

Height of tubular busbar of second level 13 m 4 mTubular Aluminium Busbar * 4” IPS 4” IPS

* It could be of suitable conductor also.

1.5 Essential Features of a Substation Back to contents page

An AC Substation has following parts:

AC Switchyard

Control Building

DC Battery System and LT Distribution System

Mechanical, Electrical and other auxiliaries

Civil works.

An HVDC substation has following main parts:

AC Switchyard

Converter Transformers

AC Filter banks

Valve Halls

AC Switchyard, Smoothing Reactor, DC Filters

Mechanical, Electrical and other auxiliary systems

Each substation is designed separately on the basis of functional

requirements, ratings, local conditions predominately based on load

centres etc. For the same requirement, several alternative designs are

possible. However, the principles and basic technical requirements of

all the substations are similar and the substation is designed on the

basis of these requirements and the earlier experience.

The Rihand-Delhi bipole project is the first commercial long distance

transmission project in India employing High Voltage Direct Current

(HVDC) Technology.

The main features of HVDC which distinguish it from high voltage AC

transmission system are:

It forms an asynchronous connection between two stations

connected through HVDC link i.e. the transmission of power is

independent of the sending and receiving end AC system

frequency. Due to this, one of the major use of HVDC is to

interconnect two regions which are usually operating at different

frequencies.

HVDC becomes economical for bulk power transfer beyond a

certain transmission distance. This is due to the fact that the DC

lines are much cheaper compared to the equivalent AC line(s)

whereas the terminal equipment of DC are costlier compared to the

AC terminal equipments.

Reduction in right of way. The DC line corridor being extremely

compact, results in reduction of right of way requirement. The total

requirement of the right-of-way reduces to about half, for the same

quantum of power to be transmitted.

The power flow through DC link can be precisely controlled under

steady state as well as dynamic conditions. During steady state

conditions, the power flow remain fixed at the ordered value and is

independent of the conditions in the AC system.

During dynamic conditions e.g. during power swings caused by

faults, the power flow through DC link can be modulated in a way so

as to assist the rest of the grid in damping the prevailing

disturbance.

Since a DC transmission line does not generate or absorb any

reactive power, it helps to increase the capability of the link to

transmit large quantities of power over long distances in an efficient

and economical manner. Due to the absence of reactive power, the

losses on a DC line are also low compared to an equivalent AC line.

Due to absence of frequency factor on DC link, the skin effect does

not play any part & complete cross section of the conductor can be

effectively used and more power can be transmitted on the same

size of the conductor. So HVDC transmission lines help in bulk

power transmission in more efficient, economical way on long

distances.

The DC transmission linens do not contribute to short circuit levels

at the terminals. This feature becomes important if two large

networks are being connected where short circuit levels are in the

vicinity of maximum values specified for the network.

In Rihand- Delhi HVDC link of Powergrid one of the converters of the project

which operates as rectifier is located in the south eastern corner of UP near

Rihand STPP. The other converter which operates as inverter is located in the

western side of UP in the district Ghaziabad at Dadri which is about 50 km from

Delhi. The project also includes two electrode stations one at Chapki, about 22

km from Rihand and the other at Dhankaur, about 25 km from Dadri. The

PLCC communication system has two repeater stations along the route of the

line: one at Katra, about 240 km from Rihand and the other at Jhinjhak, about

325 km from Dadri. The project transmits the power generated at the

Rihand/Singrauli complex to Dadri from where it is further distributed to various

beneficiaries states/union territories in the Northern Region. Typical Data of

Rihand - Delhi HVDC link is given below in Table -3.

Table 3: Typical data of Bipolar HVDC Substation (Rihand - Delhi link)

1 Rated Capacity 1500 MW2 Minimum power 40 MW/80 MW3 Operating voltage-DC + 500 kV4 AC side voltage range

For Performance 380-420 kV

For Rating 360-440 kV5 AC side frequency range

For Performance 48.5-50.5 Hz

For Rating 47.5-51.5 Hz6 Negative phase sequence unbalance

For Performance 1.0%

For Rating 2.6%7 Reduced Voltage Oprn. DC, 400 kV8 Overload rating

(For 2 hrs, available after every

12 hrs if ambient temp of Delhi

or Rihand is more than 33oC 1650 MW9 Continuous over load 1650 MW

(If ambient temp at Delhi & Rihand is less than 33oC)10 Short time over load 1000 MW Per pole

(For 5 Sec, available after every 5 min.)11 Thyristor Valves

Thyristor type YST 45

Max. Voltage per thyristor 6.5 kV

Current Rating

Continuous 1568 Amp.

2 Hr. Over Load 1725 Amp.

5 Sec. Over Load 2539 Amp.12 Converter Type 12 Pulse

13 Valve Type Quadruple Vertically

Suspended, 4 x 96 thyristors14 Quadruple per Converter 315 Cooling Water16 Converter Transformer

Type 10, 3 winding

Quantity 6 + 1 Spare per station

Rating 315/305 MVA

Tap Range + 14/-10

@ 1.25 %17 Secondary Voltage

For Delhi

Delta 206 kV

Star 119 kV

For Rihand

Delta 213 kV

Star 123 kV18 AC Filters

Numbers of Banks 3 per station

Numbers of Sub-banks 3

Size of each Bank 230 MVAR19 Oil Smoothing Reactor

Per pole per station 360 mH20 Air Smoothing Reactor

Per pole per station 180 mH21 DC Filters

Numbers per pole 2

Tuning Frequencies 12, 24 Hz22 PLCC Frequencies

Data (pole & bipole) 2400 Bauds

Per pole per station 180 mH

Repeater LAS to CU 600 Bauds

Speech 100/50 Bauds

23 Station AvailabilityDesign target 99%

Guaranteed 97%24 HVDC LINE

DC voltage + 500 kV

Configuration Horizontal bipole with a

pole spacing of 12750 mm25 Name and type of conductor ACSR “BERSIMIS” / 35.1 mm26 Number of conductors per pole 427 Insulators 160 kN HVDC disk insulator

with zinc sleeve, 38 insulators

used in each arm of ` V’ string.

Porcelain & toughened glass

insulators have been used 1.5.1 Special Features

Back to contents page

In order to integrate the project with the AC system and to help the

grid, a number of features have been incorporated into the project that

take advantages of the HVDC transmission. Some of these features

are

i) Power modulation Under normal operating conditions a part of the Northern Region

Ac system remains parallel to the Rihand-Delhi HVDC project. In

case of any disturbance in the AC system e.g. caused by faults,

switching actions, the power flow on the HVDC link is modulated

to counteract the power swings. Depending upon the need, as

determined through minimum power upto the five second

overload rating of the HVDC link.

ii) Frequency control At Rihand side, the rectifier is connected to the rest of the AC

System through two 400 kV AC lines. In case of outages of

these lines the power flow through the HVDC link is regulated to

prevent the Rihand machines from putting out of the grid and

maintain the frequency of the Rihand generators at a target

value near 50 Hz.

iii) Reactive power control This feature allows controlled switching of the available Ac

harmonic filter (s) (i) to meet the target value of reactive power

exchange with the Ac system at Rihand, and (ii) to meet the

target value of AC system voltage or reactive power exchange

at Dadri. While switching the Ac harmonic filter (s), proper care

is taken of the harmonic performance criteria, operating mode,

bipole power and the AC system conditions.

iv) Run back control The flow through the HVDC link is also regulated following

outages of AC lines at Dadri or generators at Rihand.

v) Control of sub-synchronous reasonance Suitable subsynchronous resonance damping controllers have

been incorporated to prevent any negative damping by the

HVDC at the nearby generator’s natural resonating frequencies.

This avoids any adverse interaction between HVDC and the

generators at the natural resonating frequencies.

1.6 Site Selection Back to contents page

Before the actual switchyard erection works, the land selected for

setting up the substation is acquired. A Proforma at Annexure- I gives

the Format for selection of site for Sub-Station site

Annexure-1Back to contents page

Format for Comparative Statement of Sites For Sub-Stations______________________________________________________________________________________________

Sl. No. Criteria Alternate-I Alternate-II Alternate-III______________________________________________________________________________________________

1.0 Land1.1 Size (Acre)

(Mtr. x Mtr.)

1.2 Govt. Private/Forest land

1.3 Agriculture/Wasteland

1.4 Development

1.5 Approximate cost

1.6 Type of soil

1.7 No. of owners

1.8 Environment/Pollution in the vicinity

1.9 Location with reference to nearest town

1.10 H.F.L. Data

1.11 Diversion of Nallah/Canal required

1.12 Slope

1.13 Extent of levelling required

1.14 Land acquisition feasibility

1.15 Rate of Govt. land

1.16 No. of owners

1.17 Exten. of approach

1.18 Planned/unplanned development

1.19 Size of sites

1.20 No. of families displaced

1.21 Required Government value

1.22 Level of site with ref. to road level

1.23 Distance from sea shore

2.0 Approach2.1 What are the Obstacles in reaching site

2.2 Approach road

2.3 Length of approach road

2.4 Distance from main road

2.5 Unloading facility at Railway Station

2.6 No. of Culverts required

3.0 Community Facilities3.1 Drinking Water

3.2 Drainage

3.3 a) Post Office

b) Telephone

c) Telex

3.4 Market

3.5 Security

3.6 Amendability

3.7 Availability of construction water

3.8 Availability of water

3.9 Nearest EHV line

3.10 Length of line between

this site & nearest substation

3.11 Length of line estimate

3.12 Additional crossings

3.13 Frontage for line take off

3.14 Telephone/Telegraph line

4.0 Others

1.6.1 Land Acquisition Back to contents page

Land is a state subject. Land acquisition activity starts after the

approval is obtained from the competent authority for the

recommended site. Land is to be acquired for starting the construction

activities. Typically for a 400 kV sub-station 50-80 Acre land is

required. Land being the state subject, acquisition for the sub-station

land is carried out through land acquisition deptt. of the concerned

state govt.

Brief summary of Land Acquisition Process is given below

1.6.2 Provisions Under The Land Acquisition Act, 1894 For Sub-Stations Back to contents page

When land is acquired for sub-stations, POWERGRID will follow

procedures laid down under the Land Acquisition Act (LA Act), 1894.

POWERGRID sub-stations have never resulted in large scale

displacement or loss of livelihoods. There have been only marginal

impacts due to flexibility exercised by POWERGRID in selecting sites.

The LA Act specifies that in all cases of land acquisition, no award of

land can be made by the government authorities unless all

compensation has been paid. POWERGRID has always followed a

schedule for R&R (illustrated in Table below). These will be further

reinforced taking into consideration POWERGRID’s entitlement

framework and public consultation process.Table 4: POWERGRID’s Activity Chart for Land Acquisition

and R&R Activity

Submission of cases for land acquisition

Section 4 draft notification

Spot verifications

Scope for objections from public

Publication of Section 6 draft declaration

Marking of land, notice to persons and award by Collector

Finalisation of R&R package

Payment of compensation and acquisition of land

Handing over land to POWERGRID

Implementation and completion of R&R package

1.6.3 Land Acquisition Act, 1894 as amended in 1984 Back to contents page

This is the principal law dealing with acquisition of private land by the

state for “a public purpose”. Progressive liberalisation and

industrialisation have led to an increase in compulsory land acquisition.

Land acquisition goes through a number of stages starting from

notification to payment of compensation.

POWERGRID selects a suitable substation site only after the approval

of the project by GOI. Attachment above shows the format for

comparative statements of sites to be considered for construction of

sub-stations. On the basis of data for the various parameters cited in

the checklist a comprehensive analysis for each alternative site is

carried out. Weightage given to the various parameters is often site

specific. Due consideration is given to infrastructure facilities such as

access roads, railheads etc.; type of land viz. Govt., revenue, private

land, agricultural land; social impacts such as no. of families getting

affected; and cost of compensation and rehabilitation.The Activity Chart given in the Annexure-2 shows the time frame for

the implementation of various sections of Land Acquisition Act (Section

wise time schedule) as well as the time schedule for parallel R&R

activities.


ACTIVITY CHART (TIME FRAME)LAND ACQUISITION R&R ACTIVITY

(PARALLEL ACTIVITY)SECTION 16- POSSESSION OF LAND ________ 1 MONTH LINK__________DISBURSEMENT OF COMPENSATION __________ FINALISATION OF RAP __________15 DAYSSECTION 11- AWARD BY COLLECTOR 2 MONTHS__________1 MONTH PUBLIC CONSULTATIONSECTION 9- NOTICE TO PERSONS __________ 1 MONTH COMPLETION OF S-E SURVEYSECTION 8- MEASUREMENT AND MARKING OF LAND 3 MONTHS

___________15 DAYSSECTION 6-DECLARATION OF LAND FOR ACQUISITION ____________2 MONTHS SOCIO-ECONOMIC SURVEY LINK BY POWERGRID OR

OUT SIDEAGENCYSECTION 4- PUBLIC NOTIFICATION ___________ 2 MONTHS

SUBMISSION OF CASE TO STATE GOVT. FOR ACQUISITION BY POWERGRID

1.7 Substation parts and equipment:Back to contents page

Outdoor Switchyard - Incoming & outgoing lines

- Busbars

- Transformers

- Insulators

- Substation Equipment such as Circuit-

breakers, Isolators, Earthing, Switches, Surge

Arresters, CTs, VTs/CVTs

- Neutral Grounding Equipment

- Station Earthing system comprising

ground mat, risers, earthing strips,

earthing spikes

- Overhead earthwire shielding against

lightning strokes, or, lightning masts

- Galvanised steel structures for towers,

gantries, equipment supports

- PLCC Equipment including line trap,

tuning unit, coupling capacitor, etc.

- Power cables

- Control cables for protection and control

- Roads, Railway track, cable trenches

- Station lighting system

Main Office Building - Administrative building conference room

etc.

11/ 33 kV Switchgear - 33 kV Outdoor Switchgear

11 kV Indoor Switchgear

LT Panels - Low voltage AC. Switchgear

- Control Panels, Protection Panels.

Battery room and - DC Battery system and charging

equipment distribution system

Mechanical, Electrical - Fire fighting system Oil purification

system and other auxiliaries Substation parts

and equipment:

- Cooling water system

- Telephone system

- Workshop; stores etc.

Protection system - CTs, CVTs

- Protective Relays

- Circuit breakers

SCADA(Supervisory - Computer/Microprocessors,

Data collection

Control and Data - system, Data processing system

Acquisition System) - Man-machine interface

- Expert system etc.

1.8 Functions of Sub-station Equipments & Associated Systems Back to contents page

i) Circuit BreakersCircuit Breakers are the switching and current interrupting

devices. Basically a circuit-breaker comprises a set of fixed and

movable contacts. The contacts can be separated by means of

an operating mechanism. The separation of current carrying

contacts produces an arc. The arc is extinguished by a suitable

medium such as dielectric oil, vacuum, SF6 gas. The circuit

breakers are necessary at every switching point in the

substation.ii) Isolators

Isolators are disconnecting switches which can be used for

disconnecting a circuit under no current condition. They are

generally installed along with the circuit breakers. An isolator

can be opened after the circuit breaker. After opening the

isolator, the earthing switch can be closed to discharge the

trapped electrical charges to the ground.

iii) Current Transformers and Voltage Transformers

These transformers are used for transforming the current and

voltage to a lower value for the purpose of measurement,

protection and control.

iv) Surge Arresters

Surge Arresters divert the over voltages to earth and protect the

substation equipment from over voltage surges.

v) BusbarsBusbars are either flexible or rigid. Flexible busbars are made

of ACSR conductors and are supported on strain insulators.

Rigid busbars are made up of aluminium tubes and are

supported on post insulators.vi) Galvanised Steel Structures

Galvanised Steel Structures are made of bolted/welded

structures of angles/channels/pipes. These are used for towers,

gantries, equipment, support structures etc. Galvanised

structures provide rigid support to the various equipments and

insulators. The design should be safe and economical.

vii) Power Line Carrier Current Equipment PLCC is necessary for transmitting/receiving high frequency

signals over the power line (transmission Line) for the following:

a) Voice communication

b) Data transmission

c) Protection signalling

d) Control signalling

A small power system is generally controlled by direct

supervision of generating stations and substations through

respective control rooms. A large network having several

generating stations, substations and load centres is controlled

from central load despatch centre. Digital or voice signals are

transmitted over the transmission lines via the substations. The

substations are linked with the load control centres via Power

Line Carrier System (PLCC)/ microwave links and P&T phones.

The data collected from major substations and generating

stations is transmitted to the load control centre. The

instructions from the load control centres are transmitted to the

control rooms of generating stations and substations for

executing appropriate action. Modern power system is controlled

with the help of several automatic, semi-automatic equipments.

Digital computers and microprocessors are installed in the

control rooms of large substations, generating stations and load

control centres for data collection, data monitoring, automatic

protection and automatic control.

viii) Protective Systems in SubstationsA fault in its electrical equipment is defined as a defect in its

electrical circuit due to which the flow of current is diverted from

the intended path. During the fault the impedance is low and

fault current is high. Fault currents being high, can damage the

equipments thro’ which it flows.

Fault in certain important equipment can affect the stability of

the power system. For example, a fault in the bus zone of a

substation can cause tripping of all the feeders and can affect

the stability of the interconnected system.

The relays distinguish between normal and abnormal condition.

Whenever an abnormal condition develops, the relay closes its

contacts. Thereby the trip circuit of the circuit breaker is closed.

Current from the battery supply flows in the trip coil of the circuit

breaker and the circuit breaker opens and the faulty part is

disconnected from the supply. The entire process, ‘occurrence

of fault-operation of relay opening of circuit breaker to removal

of faulty part from the system’ is automatic and fast. Besides

relays and circuit breakers, there are several other important

components in the protective relaying scheme, these include :

protective current transformers and voltage transformers,

protective relays, time delay relays, auxiliary relays, secondary

circuits, trip circuits, auxiliaries and accessories, etc. Each

component is important. Protective relaying is a team work of

these components.

The function of different substation equipments and systems

are tabulated below in Table -5.

Table 5: Functions of different Substation Equipments & Systems

Sl.No.

Equipment Function

1. Bus-bar Incoming and outgoing circuits connected to bus-bar2. Circuit-breakers Automatic switching during normal or abnormal

conditions.3. Isolators

(Disconnectors)

Disconnection under no-load condition for safety,

isolation and maintenance.4. Earthing Switch To discharge the voltage on dead lines to earth.5. Current

Transformer

To step-down currents for measurement, control, and

protection.6. Voltage

Transformer

To step-down currents for measurement, control, and

protection.7. Lightning Arrester

(Surge Arrester)

To discharge lightning over voltage and switching over

voltage to earth.8. Shunt reactor To provide reactive power compensation during low

loads.9. Series Reactors To reduce the short-circuit current or starting currents.10. Neutral-Grounding

Reactors

To limit the earth fault current

11. Coupling capacitor To provide connection between high voltage line and

power line carrier current equipment.12. Line-trap To prevent high frequency signals from entering other

zones.13. Shunt capacitors To provide compensations to reactive loads of lagging

power factors.14. Power Transformer To step-up or step-down the voltage and transfer power

from one AC voltage to another AC voltage at the same

frequency.15. Series capacitors Compensation of long lines

16. Substation

Earthing

(Grounding)

System

-Earth mat

-Earthing spikes

-Earthing risers

To provide an earth mat for connecting neutral points,

equipment body, support structures to earth. For safety

of personnel and for enabling earth fault protection. To

provide the path for discharging the earth currents from

Neutrals, Faults, Surge arresters, overheads shielding

wires etc. with safe step-potential and touch potential.

17. Overhead earth

wire shielding or

lightning Masts.

To protect the outdoor substation equipment from

lightning strokes.

18. Illumination system

(lighting)

-for switchyard

-buildings

-roads, etc.

To provide illumination for vigilance, operation and

maintenance.

19. Protection System

-protection relay

panels

-control cables

-circuit-breakers

-CTs, VTs, etc.

To provide alarm or automatic tripping of faulty part from

healthy part and also to minimise damage to faulty

equipment and associated system.

20. Control cabling For protective circuits, control circuits, metering, circuits,

communication circuits. 21. Power cables To provide supply path to various auxiliary equipment

and machines.22. PLCC system

power line carrier

current system

-line trap

-coupling capacitor

-PLCC panels

For communication, telemetry, tele-control, power line

carrier protection etc.

23. Fire fighting

system

-sensors, detection

system

-water spray

system

-fire protection

control panels,

alarm system

-water tank and

spray system

To sense the occurrence of fire by sensors and to initiate

water spray, to disconnect power supply to affected

region to pin-point location of fire by indication in control

room.

24. Cooling water

system(HVDC)

-coolers

-water tank

-piping

-valves

This system is required for cooling the valves in HVDC

substation.

25. Auxiliary stand by

power system

-diesel generator

sets

-switchgear

-distribution

system

For supplying starting power, stand by power for

auxiliaries.

26. Telephone, Telex

system,

Microwave

system

For internal and external communication.

1.9 Substation Layouts, Busbar Schemes Back to contents page

The term layout denotes the physical arrangement of various

components in the substation relative to one another. Substation

layout has significant influence on the operation, maintenance, cost

and protection of the substation and these aspects are considered

while designing the substation layout.

The reasoning behind the connections of components in each circuit

and the busbars layout should be understood. Within the frame-work

of the basic requirements, the substation layout can have several

alternative arrangements. The substation layouts are selected on the

basis of the size, the ratings, importance, local requirements and the

prevailing practice of the supply authorities. The different bus-bar

schemes in a substation with their relative advantages/disadvantages

are described below:

The choice of busbar schemes for AC yards depend upon several

factors mentioned above. The important busbar schemes include the

following:

Single busbar

Double busbar with one breaker per circuit.

Double busbar with two breakers per circuit.

Main and transfer bus

Ring bus

Breaker and a half arrangement

Mesh arrangement etc.

Table : 6 Various Bus-Bar Schemes

Sl.No.

Scheme Application Remarks

1. Single bus-bar Low voltage and medium

voltage substations

Not preferred for important/

large substations

- Cheapest

- Total shutdown in case of a

fault

- In case of maintenance of

circuit breaker, associated

feeder has also to be shut

down 2. Duplicate Bus High voltage substations - Costlier than single bus

- One bus can serve as a

reserve.

- During maintenance or

fault, the reserve bus is

used

- More flexibility of operation

- Buses are sometime

sectionalised & the bus

coupler breaker is

connected in between two

buses3. Double Main

and Transfer

Bus

Important EHV substations - Additional flexibility for

operation

- Fault on one bus will not

cause a complete outage of

the station.4. Breaker & a

half scheme

Important 400 kV

substations

- Uses three breakers for two

circuits

- High flexibility operations

- Higher costs

- Suitable for those

substations which handle

large amounts of power on

each circuit

5. Mesh System Used for large substations

having many incoming and

outgoing circuits.

- Costlier

- Gives good

operational flexibility

- Suitable where no. of

circuits are comparatively

few & chances of future

expansion are less

1.10 Construction/Erection DrawingsBack to contents page

Lists of construction/erection drawings used during Civil and other

construction activities in a substation are enclosed at Annexure-3 and

Annexure-4.


A. Control Room Building1. Ground floor Plan & Elevators

2. Mezzanine Floor Plan & Elevations

3. Elevation, Section & Terrace Plan

4. Foundation Plan-Excavation drawing

5. Foundation & column up to first floor

6. Details of plinth beams

7. Mezzanine floor beams & reinforcement details

8. Mezzanine floor slab & reinforcement details

9. Mezzanine floor insert details

10. Lintel & Chhajja details

11. Roof slab reinforcemet details

12. Roof beam details

13. Roof slab insert details

14. Details of foundation for A/C plant room

15. GA & RCC details of foundation for cooling tower supporting structure

16. Internal cable trench details

17. Details of steel & window details

18. Aluminium glazing window details

19. Fire resistance door/siding door details

20. Details of toilet & pantry

21. Plumbing details

22. Details of septic tank

23. Finish schedule

24. Colour scheme

25. Electrical wiring drawings

B. DG Set Building1. Plan elevations and sections

2. Foundation layout and RCC details of slab flooring, columns, beams.

3. Details of brick wall foundation, columns and intel.

4. Details of doors and windows.

5. DG set foundation and cable trench layout and R/F details.

6. Colour scheme and misc. details, monorail fixing details.

7. Electrical wiring, insert fixing details.

C. F.F. Pump House1. Plan, elevation and sections

2. Foundation layout, RCC details of slab, footing, column beam.

3. Terrace plan and Misc. Details.

4. Details of water tanks.

5. Details of doors, window, ventilators and rolling shutters.

6. Equipment foundation, cable trench layout and reinforcement details.

7. Electrical wiring drgs., insert details.

D. Internal Roads and Drains1. Layouts of internal roads and drains.

2. Layouts and cross sectional details of roads and drains.

3. Layout of culverts and drains.

4. Details of culverts and drains.

E. Boundaries Wall and Fencing1. Boundaries wall and fencing details

2. Fencing and gate details

F. Shunt Reactors1. GA and foundation details.

2. Pylon support details

G. Auto Transformer1. GA and RCC details of foundation, General arrangement

2. Pylon support details

3. Details of rail track

4. Fire protection wall between auto-transformer

H. Approach Roads and Drains1. Layout of approach roads and drains.

2. Layout and C/S details of roads and drains.

3. Layout of drains and culverts

4. Details of culverts and drains.

I. Site Office and Store Complex1. Material store plan, Elevation and sections

2. Crane store plan, Elevationa and Sections.

3. Site office plan, Elevation and sections.

4. S/S store Plan, Elevation and sections.

5. Cement store Plan, Elevation and sections.

6. Details of raised platform.

7. Store complex layout plan.

8. Store complex TL material store.

9. Store complex TL material store.

10. Crane store foundation plan, roof plan and beam details.

11. S/S store foundation plan, roof plan and beam details.

12. Cement store foundation plan, roof plan and beam details

13. Details of entrance gate and fencing

14. Type section of tabular truss.

15. Details of doors and windows.

16. Finish schedule of site office and store complex.

17. Layout ext. drainage and sewerage system

18. Details of septic tank and soakpit.

19. Toilet and kitchen detail-site office

20. Toilet and kitchen details-S/S. store

J. Structural arrangement1. Design of towers and beams

2. Fabrication drawings of tower & beams

3. Tower foundation and their designs

4. Design of equipment supporting structure

a) CT

b) CVT

c) LA

d) Bus Post Insulator

e) Isolator

f) Wave Trap

g) Circuit Breaker

5. Equipment supporting structure fabrication drawings

a) CT

b) CVT

c) LA

d) Bus Post Insulator

e) Isolator

f) Wave Trap

g) Circuit Breaker

6. Details of foundation bolts

a) Equipment Structure

b) Gantry Structure

7. Design of equipment foundations & foundation details

8. Cable trench layout

9. Cable trench section details

10. Cable trench road crossings

11. Marshalling box foundation

12. Sump pit

List of construction Drawings for Township Work in a typical Sub-station

A. Quarters for Type A,B, C and D1. Architectural plan, Elevation

2. Architectural section, terrace plan

3. Foundation plan, Plinth beam layout

4. Details of foundation

5. Details of roof slab, first floor slab, lintel etc.

6. Electrical layout

7. Sanitary layout and plumbing details

A. Master Layout1. Plan

2. Electrical layout

3. Sewerage layout

4. Plumbing layout

5. Layout of drains and road.

B. Overhead and underground Water-Tank1. Architectural Drawings’

2. Structural details

3. Foundation Details

C. Non Residential Buildings(Nursery school, Dispensary and shopping centre)

4. Architectural plan and Elevation

5. Structural Details

6. Services

D. Administrative Building7. Architectural plan and Elevation

8. Structural details

9. Services


List of drawings for a typical Sub-stationA. Sub-Station Drawings1. Single line diagram

2. General arrangement of substation’

3. Electrical layout (Plan and Section)

4. Electrical clearance diagram

5. Switchyard structural layout arrangement

6. Layout of equipment structures

7. Busbar support design and design calculations

8. Cable trench layout and foundation plan

9. Details of cable trench section

10. DSLP calculation

11. Drawing of DSLP scheme

12. Earthmat design calculation

13. Equipment/structure earthing details

(List all relevant drawings, under this heading)

a) Earthmat layout

b) Erection key diagram (Plan and Section)

c) Bill of Quantity

14. Short circuit force and critical span calculation(for spacers)

15. Design calculation for sag-tension and stringing chart

16. Power cable schedule

17. Inter pole cable schedule

18. Buried cable trench layout

19. OGA drg. for bus post insulator

20. Individual insulators detail drg. for bus post insulator

21. Detail drg. for bottom & inermediate flanges

22. Cap detail drg. for bus post insulator

23. Corona ring for bus post insulator

24. GA of bay marshalling kiosk

25. Schematic & wiring diagram of bay marshalling kiosk

26. Tension/suspension string insulator and hardware assembly

27. 120KN antifog disc insulator GA drg.

28. Clamps, connectors and spacers GA drg.

29. ACSR conductor, Al tube & shieldwire

30. GTP data sheets

31. Cable trays GA drawing

32. GA drg. for double compression type cable gland

33. Drum drg. for ACSR conductor and earthwire

B. 245KV SF6 Circuit Breaker1. Outline general arrangement drawing of C.B. indicating major parameters.

2. Outline general arrangement drg. of control cabinets and their foundation plan

and separate drawing showing component layout.

3. Outline general arrangement drg. of support insulator.

4. Interrupter insulator, insulator & insulator for grading capacitor showing clearly

the shed profile and parameters.

5. Support structure and foundation plan drawing with necessary support

structure design calculations.

6. Electrical schematic diagram including brief write up on operation.

7. Rating and name plate drawing.

8. Air/SF6 gas connection diagram

9. Schematic diagram of electro hydraulic operated mechanism in case of

hydraulic drive.

10. Wiring diagram

11. Terminal conenctor and corona ring drawings

12. Sectional view of SF6 gas couplings.

13. Sectional view of interruptor, voltage grading device identifying each part of

the assembly.

14. Following additional drawings for Unit air compressor:

a) Foundation plan and details for compressor and motor

b) Unit of contact manometer assembly.

C. 245KV Isolator1. Outline drawing of isolators with one E/S

2. Outline drawing of isolators with two E/S

3. Outline drawing of isoaltor without E/S

4. General arrangement of contact assembly.

5. Terminal pad and hinge contract.

6. Loading data.

a) GA of motor operated mechanism

b) GA of support insulator

7. Details of constructional interlock

8. Name Plate details

9. Drawings for terminal connector & corona rings.

10. Drawing for base frame.

11. Schematic drawings.

12. Wiring diagram & inerpole connection diagram.

13. Drawing for motor operated mechanism/manually operated mechanism, as

applicable with door open and identifying all parts of the mechanism and the

control panel.

14. Drawing for support structure.

D. 245KV Current Transformer1. Outline drawing of C.T. indicating major parameters.

2. Sectional view of C.T.

3. OGA of marshalling box

4. OGA of secondary terminal box

5. Wiring diagram of marshalling box(including interpole wiring).

6. Magnetisation curve.

7. Name plate.

8. Drawing of terminal connectors.

9. Drawing of corona ring.

10. Drawing for stool/sub-structure, if applicable.


E. 245KV Capacitor Voltage Transformer1. Outline drawing of CVT indicating major parameters.

2. Sectional view of CVT.

3. OGA of secondary terminal box.

4. OGA of marshalling box.

5. Wiring diagram of marshalling box (including interpole wiring)

6. Drawing for terminal connectors

7. Name plate drawing.

8. Drawing for stool/sub-structure, if applicable.


F. 245KV Class Surge Arrester1. OGA of Surge Arrester indicating major parameters.

2. Foundation details.

3. Insulating base drawing.

4. Discharge counter/surge monitor drawing

5. Method of connecting surge monitor with SA

6. Electrial schematic diagram of surge monitor

7. Ground terminal bracket details

8. Name plate drawing

9. Line teminal bracket drawing along with corona rings

10. Residual voltage verses discharge current curves

11. Drawing for stool/sub-structure, if applicable

12. Drawing showing internal view of SA

13. Drawing of Insulator

14. Drawing showing pressure relief arrangement

15. Support structure drawing.

G. Power and Control Cables1. Data sheet of all types of power cables

2. Data sheet of all types of control cables

3. Power cable schedule

4. Control cable sizing/section criteria

5. Control cable laying & termination schedules

List of Drawings for Erectin of C&R panels in a typical Sub-Station

1. Data requirement sheet with literature.

2. Type test report for all equipments.

3. Board formation redrawings.

4. Foundation details.

5. General arrangement of control panel/feeder.

6. General arrangement of relay panel/feeder.

7. Schematics of control panel/feeder.

8. Schematics of relay panel/feeder.

9. Cable schedule.

a) Inter panel schedule.

b) Cable laying schedule.

c) Cable terminating schedule.

10. Equipment layout drgs.

11. Relay settings.

12. As built drgs. And manuals for circulation.

List of drawings for Erection of PLCC panels in a typical Sub-Station

1. Data requirement sheet with literature.

2. Type test report for all equipments.

3. General arrangement of PLCC system.

4. Equipment drgs.

a) PLCC panel for speech and data.

b) PLCC panel for speech and protection.

c) Protection couplet.

d) Wave Trap.

e) Coupling Device.

f) EPAX

g) 4 wire/2 wire Telephone

5. Frequency Plan

6. As built drawing

Chapter-2SWITCHYARD CIVIL WORKS

CHAPTER TWO

SWITCHYARD CIVIL WORKS



Civil works in a substation mainly comprise of :

Construction of equipment foundations transformer/reactor plinth,

structure foundations

Cable trenches

Fencing around switch yard

Surface treatment, ground filling and sloping

Water supply system & Sewerage system

Construction of roads and drains

Construction of control room building, compressor room, offices,

repair / maintenance bay and other non-residential buildings

Construction of railway, siding and railway track if required

Construction of residential colony

Horticulture works

Administrative Building, community centre, guest house/transit

Camp, shopping complex & nursery school etc.

For carrying out the various civil works at site which is initially an open

barren/cultivated land, initially survey of land is carried out alongwith

the soil investigation. Survey is done to finalise the levels of switchyard,

roads and design & layout of drainage system in the switchyard as well

as in the township. Fix & permanent bench mark is provided for

adopting it as a reference point for various works like laying out of

control room, erection of gantries and various equipments, foundations

and buildings in the switchyard that are done in reference to this

permanent bench mark. Now grid lines are required to be marked in

East-West and North-South direction by erecting the concrete grid

pillars. Grid lines are marked on the land to fix the direction &

orientation of various civil structures with reference to some fixed

bench mark on the site. These gridlines help in implementing the

erection, orientation and layout of foundations for various equipments &

control room building which is later on helpful in laying out the other

equipments and structures on the land.

2.1 Soil Investigation Back to contents page

Soil investigation is carried out at site and result of soil investigation

are forwarded to Corporate Centre for design of various

foundations.

Detailed soil investigation is carried out at site to arrive at

sufficiently accurate, general as well as specific information about

the soil profile and necessary soil parameters of the site in order

that the foundations of various structures can be designed and

constructed safely & rationally.

The soil investigation tests should be conducted at all the critical

locations i.e. control room building, auto transformer, shunt reactor,

lightening masts, 400 KV tower locations etc.

Engineering department at Corporate Centre prepares the

foundation drawings and approved drawings are sent to site for

casting.

Engineering Department also releases various other erection

drawings for different works like cable trench design drawings,

cover slab design drawings, overall layout of equipments in

switchyard, equipments erection key drawings etc. for erection

works at site. During this period, the site levelling work is carried

out at site in order to smoothen the undulations.

2.2 Levelling Back to contents page

The land acquired for substation may be barren/cultivated land. The

soil may be rocky, black cotton, sandy or any other type. The acquired

land may contain trees, bushes, crop, drains, etc. that require cleaning/

clearing before starting the levelling works in the yard.

i) Switchyard area is important and preferably it should be brought to

a single level. However, in only unavoidable circumstances or

where it is uneconomical to go for levelling the soil than keeping a

multi-layered/in steps levels, the different levels may be kept.

ii) Levelling may also be required in township area for bringing the

land to a single level for designing the drainage system and

residential quarters. In case of too much level difference the

residences (categories) may be designed at different uniform levels

but with good drainage system to avoid water logging.

iii) Before starting the levelling works the marked area of switchyard is

cleaned. Any crop, bushes, trees, shrubs and structure that may

cause hindrance or that are undesired are cleared from the yard

area.

iv) Any drain, telephone line, building structure is also removed from

the switchyard area, to a nearby suitable place.

v) Now spot levels will have to be taken in the yard area before

making an assessment for the levelling i.e. for assessing the

requirement of soil for low level areas and cutting of soil from high

level area to bring the whole yard area to a normal formation level.

vi) In the ideal case of levelling there is no requirement for borrowed

earth and quantity of earth excavated from the high level and fill it in

the low lying areas is equal. This is the most economical method of

levelling. Care is to be taken such that the earth is not excavated

below the formation level.

vii) For compaction earth is filled in the low lying areas in layers of 20

cm thickness then watered and compacted by rollers/ dozers.

viii)The method and equipment used to compact the fill material to a

density that will give the allowable soil bearing pressure required for

the foundations, roads, etc. In each layer of fill material. Each layer

of earth embankment when compacted should be as close to

optimum moisture as practicable. Embankment material which

does not contain sufficient moisture to obtain proper compaction

should be wetted. If the material contains an excess of moisture,

then it should be allowed to dry before rolling by hand

rollers/dozers. No compaction is carried out in rainy weather.

ix) Sometime in hills or in rocky soil, we may have to go for blasting the

earth at higher levels. The blasting is done in the specified manner.

All safety precautions should be taken while blasting so as to avoid

any injury/loss of life and property. The explosive material used for

blasting should be handled very carefully. While applying the

explosive material for blasting, one should take care such that the

earth excavated/hole created by blasting is upto/very near the

desired ground level.

x) The levels in the entire area (after finishing the levelling work)

should be taken and checked up with the desired formation level.

Final dressing up and finishing should be done in case if levels are

not found satisfactory. The care should however be taken during

compaction. Measurement for levelling work (i.e. excavation &

filling) is a cumbersome process and it should be done strictly as

per the specifications. All the level records must be noted in field

levelling book duly signed by the concerned personnel of contractor

of site. The drawings of level before starting the levelling and then

final levels should be maintained. The measurements should be

recorded very carefully as per the technical specifications. Care

should be taken that with the movement of trucks, dozers etc. any

other structure in the vicinity is not affected or uprooted.

2.3 Foundations Back to contents page

Foundations in switchyard area the foundations are cast for:

i) Lattice Structure (Tower foundations) i.e. for gantries, lightening

masts etc.

ii) Cable trenches

iii) Equipment in switchyard

Based on the approved layout drawings furnished by Corporate

Engineering the foundations are marked on the ground.

While marking the foundations on the ground their layout should

be strictly verified with the layout drawings as well as with the

bench mark/grid lines on site with great accuracy.

Layout of the various switchyard equipments is also verified with

the layout drawings and with respect to gridlines on the ground.

For further confirmation, the control room building co-ordinates

can be used and necessary rectification in the layout & orientation

of various equipments and foundation can be made.

Any changes in layout if desired should be brought in the notice of

Corporate Engineering and necessary amendments should be

approved. It is a good practice to have a second confirmation for

marking the various foundations w.r.t. control room co-ordinates

that are fixed and marked before hand.

Foundations for various lattice structure are cast in the switchyard

area. The type of foundation is decided based on the type of soil.

Engineering Department at Corporate Centre provides the

necessary tower foundation, excavation and concreting work

drawings based on the soil investigation reports furnished to

them.

2.4 Foundations for Transformer & Shunt Reactors Back to contents page

i) Transformer of 400/220/33 kV, 315 MVA capacity is generally

provided at our substation sites. Transformer and shunt reactors

are the major equipments in switchyard. Their transportation,

storage, foundation and installation require special techniques

and efforts.

ii) Transformer & shunt reactor foundation work includes the supply

of a permanent track system to enable the replacement of any

failed unit by the spare unit located at the site. It also includes the

concreting, providing jacking pads, steel work for the MS grating

and providing the anchoring arrangement.

iii) The foundations for transformer & shunt reactor should be ready

in advance before actual receipt of the equipments. Proper co-

ordination in the works are required so that the foundations are

completed well in advance.

iv) For casting the foundation of Transformer & Shunt Reactor the

marking is done as per the approved drawings from the Corporate

Engineering Department. The marking of co-ordinates should be

checked properly and reconfirmed with the control room and

switchyard layout co-ordinates. The pylon supports that are

required to be laid before the concreting works is generally in the

scope of fire fighting contractor. Scheduling of such works should

be co-ordinated between the contractors for smooth working & to

avoid any stoppages in work.

2.5 Cable Trenches in Switchyard Back to contents page

i) The cable trench drawings are received by site from the

Corporate Engineering Department Based on these drawings

cable trenches are cast at site.

ii) The cable trenches are marked on ground and excavation is

started by the contractor on the marked trenches.

iii) Before starting the RCC the land should be levelled, smoothened

and then laid with PCC of required thickness. Proper care should

be taken during RCC casting.

iv) The centre line of cable trench (marked before excavation) should

be rechecked during the lean concerning to avoid any mistakes in

marking.

v) The slope in cable trenches is provided in such a way that the

water from secondary cable trenches flows towards the primary

cable trenches. The slope of primary cable trench is maintained

in such a way that the rain water may go in a sump on the other

side of the primary cable trench by gravity itself.

vi) Before starting the concreting, shuttering is provided for cable

trench walls. Provision should be made at this time to insert the

cable supporting angles and other steel reinforcements in the

cable trench walls.

vii) Concreting of cable trenches can be started after all the wall

inserts bends etc. have been inserted properly. Necessary

expansion joints generally made up of PVC or specified material

of designed size should be inserted at the specified length of

cable trench walls.

viii) Top of the trenches is kept at least 150 mm (or as specified)

above the furnished ground level such that the surface rain water

does not enter the trench.

ix) All metal parts inside the trench are connected to the earthing

system.

x) Trench wall should not foul with the foundations. Suitable clear

gap is maintained.

xi) A slope of 1/500 is provided in the trench bed along the run and

1/250 perpendicular to the run or as specified.

xii) All construction joints of cable trenches i.e. between base slab to

base slab & the junction of vertical wall to base slab as well as

from vertical wall to wall and all the expansion joints are to be

provided with approved quality PVC water stops of the specified

size. This is required in all the sections where the ground water

table is expected to rise above the junction of base slab and

vertical wall of cable trenches.

xiii) All the inserts exposed surfaces are be brushed with metal wire

brushes.

xiv) Cable supports are welded at the right level and painted with the

specified paint.

xv) All cable trenches are cleaned after the cable trench work is

completed.

2.6 Cable Trench Cover Slabs Back to contents page

i) Precast removable concrete covers are to be provided on the

cable trenches.

ii) These covers slabs are designed to cover the open trenches in

which cables are placed.

iii) Concrete cover slabs are cast by using metallic shuttering of

suitable size.

iv) The shuttering should not be deformed otherwise cover slabs will

also be deformed and become out of shape.

v) After casting the slabs, shuttering should be removed after 24 hrs.

and proper curing of cover slabs should be done for at least 10

-14 days.

vi) Cover slabs are placed over the cable trenches after the cables

have been laid.

vii) The cover slabs over cable trench are joined with cement mortar

and generally the tenth cover in a line is kept free from joining

with provision of lifting hook. This is done so that the covers can

be removed for regular inspection of cable trenches during

maintenance.

viii) Cover slabs are placed on cable trenches after completion of

cable laying.

2.7 Anti-weed Treatment, Micro Levelling Gravel Filling & Metal Spreading Back to contents page

2.7.1 Anti-weed Treatment Back to contents page

i) The soil of the entire switchyard area is subjected to

sterilisation/anti-weed treatment before the site surfacing/gravel

fill material. The treatment is done strictly as per instruction of the

manufacturer of the chemical required for soil sterilisation/anti-

weed treatment.

ii) After all the structures and equipments have been erected and

accepted, and soil sterilisation (as specified) is complete, the site

should be maintained to the lines and levels and

rolled/compacted by using roller of specified capacity with

suitable water sprinkling to form a smooth and compact surface

condition which should match with finished ground level of the

switchyard area.

2.7.2 Micro Levelling Back to contents page

i) After the soil sterilisation and application of anti weed treatment

the surface is prepared for levelling to the required level.

ii) The switchyard are is used by various contractors & executing

agencies for the various works like laying of earth mat excavation,

foundation casting & backfilling of earth, equipments erection,

cable laying in the cable trenches and piping work for fire fighting

systems.

iii) After completion of different works the various agencies working

in switchyard should remove their set up like construction power

cables, water pipe lines, sand, metal & other construction

materials and T&P etc.

iv) The heavy vehicles like cranes, trucks and other transport modes

move in the switchyard area. This movement causes a change in

the switchyard level causing lot of undulations in the earth level.

The earth that was earlier levelled now again requires some fine

levelling to bring it back to original finished desired level.

v) This process of removing the surplus earth and filling it at the low

lying areas so as to maintain one level is done after completion of

various works in switchyards. This laid earth is then duly

compacted.

vi) The method of compaction is same that water is poured over, the

layer of specified check thickness of earth and the layer of such

earth is then compacted using compaction tools. Again a layer is

laid and water is poured in it and the earth is again compacted.

vii) This process of refilling and compaction goes on until the required

level of earth is achieved. Care should however be taken that

during excavating the excess earth (for refilling at the low level) the

earth is cut and removed only upto the required level and not

below otherwise this area may again require some refilling causing

wastage of labour.

viii) The important thing in micro levelling is the backfilling and

compaction. If both are not done properly the earth level may

come down after some time (after rains etc.) making it low lying

area. In case of some reservations over the degree of compaction

of backfilling the specified tests can be performed.

2.7.3 Metal spreading in Switchyard Back to contents page

i) The area where metal spreading is to be done is measured for

quantity of metal required for filling.

ii) Hard granite store of 40 mm nominal size is spreaded in different

stages. Under size and over size metal should be rejected.

iii) The metal stacks are placed at a designated place and these are

measured and recorded before actually spreading in the

switchyard metal is spreaded in the layers of 100 mm.

DO’S DON’T’S&

SPECIAL PRECAUTIONS

2.8 Do’s , Don’ts & Special PrecautionsBack to contents page

i) Whenever water table is met during the excavation, it should be

dewatered and water table maintained below the bottom of the

excavation level during excavation, concreting and backfilling.

ii) The method and equipment used to compact the fill material should

be suitable to achieve the density that will give the allowable soil

bearing pressure required for the foundations, roads etc. In each

year of fill material.

iii) Minimum 75 mm thick lean concrete (1:4:8) or as specified should

be provided below all underground structures, foundations,

trenches etc. To provide a base of construction.

iv) Necessary protection to the foundation work, if required should be

provided to take care of any special requirements for aggressive

alkaline soil, black cotton soil or any other type of soil which is

detrimental/harmful to the concrete foundations.

v) RCC columns should be provided with rigid connection at the base.

vi) Only approved admixtures should be used in the concrete for the

Works. When more than one admixture is to be used, each

admixture is batched in its own batch and added to the mixing water

separately before discharging into the mixer.

vii) The water-reducing set-retarding admixture if used should be of

approved brand

viii)The water roofing cement additives shall be used as

required/advised by the consignee.

ix) The concreting of trench should be arranged for a length of not

more than 30 mtrs. at a time.

x) Bar bending schedule for raft and trench wall should be prepared as

per the drawing and same should be checked for placement.

xi) To meet the commissioning schedules, the priority areas are to be

identified and the construction of foundations and cable trenches

should be taken up in stages and priority-wise.

xii) Wherever earth mats are crossing the cable trench suitable U

bends of MS rounds should be placed below the trench raft before

concreting.

xiii)A separate sump should be constructed for curing the cover slabs.

xiv)The cover slab should be kept in water sump for a period of about

10 days for curing.

xv) Due care should be taken so as not damage any foundation

structure or equipment during rolling/compaction.

xvi)The gravel should be allowed to come from one or two approved

quarries where the similar gravel availability is possible.

xvii)The stone should be hard, coarse and it should not be flat.

xviii)The quantity required to fill up a measured area should be

ascertained actually. Then the metal of adequate measurement

should be spread in this area.

xix)Use of undersize & oversize metal than the specified size should be

avoided. A 20 mm sieve can be used to remove the oversized

gravel.

xx) The material required for site surfacing/gravel filling should be free

from all types of organic materials and should be of standard

approved quality, and as directed by the Engineer-in-charge.

xxi)The rail and concrete sleepers are required for providing the track

for transformer and shunt reactor unit. These items are required to

be procured from the market. The items are of specific dimension

and requirement. Their availability in the open market may not be

easy so efforts to procure these items should be started

simultaneously while the works for foundation are started.

CHECK FORMAT

2.9 Check FormatBack to contents page

1. Soil investigation report has been approved by competent authority Yes/No

2. Construction drawings are being released by Engg. deptt. Yes/No3. Grid pillars are erected at site. Yes/No4. Grid lines are formed as per designed layout at site Yes/No5. Centre line marking for cable trench is checked as per drawing Yes/No6. Proper slope of main and all secondary cable trenches is

maintained

Yes/No

7. Bar bending schedule trench walls and raft is approved Yes/No8. Nosing angles and inserts for fixing cable supports have been

provided in trench wall

Yes/No

9. For concreting proper shuttering is provided in cable trenches Yes/No10. Required water stoppers at the specified trench length has been

provided

Yes/No

11. Concreting of trenches/raft done as per specifications Yes/No12. U bends have been provided in cable trenches where these cross

the earth mats.

Yes/No

13. For equipment foundations location exact co-ordinates are verified Yes/No14. All levelling work is complete before start of foundations Yes/No15. All materials like sand, cement, metal, foundation bolts etc. are

available with adequate T&P before start of foundation activities

Yes/No

16. Cable trench cover slabs being cast on special platform and with

proper shuttering

Yes/No

17. Proper curing of cover slabs is being done Yes/No18. When placed on trenches (after cable laying etc.) joints have been

sealed

Yes/No

19. For transformer & shunt reactor foundations pylon supports have

been provided by the concerned agency

Yes/No

20. Layout of foundation is verified with switchyard layout drawing Yes/No21. Rail and sleepers have already been procured before start of

concreting at site

Yes/No

22. All cable trench work, backfilling and cable trench cover slabs have

been provided

Yes/No

23. Earth mat work is complete Yes/No24. Site is cleared from any construction material and power cables and

all T&P has been removed from site

Yes/No

25. Microlevelling work is being done satisfactorily and the desired site

level is achieved

Yes/No

26. Earth required for low lying area is being cut from high level areas Yes/No27. Proper compaction of land as per specifications is being done Yes/No28. Before micro levelling all foundations have been properly backfilled Yes/No29. All metal/hard granite is properly stacked for recording Yes/No30. Hard granite metal store of specified size is spreaded Yes/No31. Metal is being brought from the selected/approved queries Yes/No32. Proper level marks for spreading and measurement of metal have

been provided

Yes/No

33. Metal spreading is completed and proper recording/measurements

have been taken

Yes/No

CHAPTER-3SWITCHYARD EARTHING

___________________________________________________________________________ CHAPTER

THREE___________________________________________________________________________

SWITCHYARD EARTHINGBack to contents page


The object of earthing is to maintain a low potential on any object. The

purpose of a earthing system in a substation area is to limit the

potential gradient within and immediately outside the area to a value,

safe for the working personnel. Safety is to be ensured under normal

as well as abnormal operating conditions.

3.1 Functional Requirements of Earthing System Back to contents page

To provide earth connection for the neutral points of transformer, reactor,

capacitor banks, filter banks, generators.

To provide discharge path for lightning overvoltages coming via rod-gaps,

surge arresters, shielding wires etc.

To provide low resistance path to earthing switch earthed terminals, so as to

discharge the trapped charge to earth prior to maintenance or repairs.

To ensure safety of operating staff by limiting voltage gradient at ground level in

the substation.

To provide a sufficiently low resistance path to earth to minimise the rise in

earth potential with respect to a remote earth-fault. Persons touching any of

the non-current carrying earthed parts shall not receive a dangerous shock

during an earth fault. Each structure, transformer tank, body of equipment etc.

should be connected to earthing mat by their own earth connection.

3.2 Earthing System in Switchyard Back to contents page

Following basic requirements are to be satisfied as so to ensure a

proper and sound earthing system in substation switchyard.

i)The earth resistance for the switchyard area should be lower than a certain limiting

value “Ra” in order to ensure that a safe potential gradient is maintained in the

switchyard area and the protective relay equipments operate satisfactorily. For major

switchyards and substations in India, this limiting value of earth resistance (Ra) is

taken to be less than 0.5 ohm.

ii)The grounding conductor material should be capable of carrying the maximum

earth fault current without overheating and mechanical damage. The maximum fault

level in the 400 KV system has been estimated to be 40 kA and this value of fault

current is used in the design of earth mat for the 400 KV substation.

iii)All metallic objects which do not carry current and installed in the substation such

as structures, parts of electrical equipments, fences, armouring and sheaths of the

low voltage power and control cables should be connected to the earthing electrode

system.

iv)Mechanical ruggedness of the ground conductor should be ensured.

v)The design of ground conductor should take care such that whenever a fault

occurs in substation, fault current flows through the faulty circuit to the connecting

electrode.

3.3 Step and Touch Potential Back to contents page

Any person in the substation area is likely is encounter the following

potential rises.

i)The station earthing system should have earth resistance lower than 0.5 ohm for

effective discharge of lightning over voltage to earth.

ii) Grounding mesh is provided below ground level. Earth electrodes are

driven into ground at several points and are connected to the

grounding mat to form Earthing Mesh. All the structures, transformer

tanks, etc. are connected to this mesh.

3.3.1 Step potentialBack to contents page

The potential difference between two steps of a person standing on the

substation floor during the flow of earth fault current is known as step

potential.

3.3.2 Touch potential Back to contents page

The potential difference between a step and the tip of the raised hand

touching a substation structure during the flow of the earth fault current

through the latter is known as touch potential.

The step potential and touch potential depend upon the following

aspects:

Earth fault current

Duration of earth fault

Whether short time (less than 3 sec.)

Whether sustained (more than 3 sec.)

Fault current flowing through body

Values of body resistance in the path

The design of grounding system should be such that the voltage

gradient in volts/metre on the surface of the ground should be less than

the permitted value.

3.4 Soil Resistivity Measurement Back to contents page

The earth resistivity is measured by driving 4 electrodes in ground in a

straight line at equal spacing of 20-25m (Fig. 1). These electrodes are

connected to terminals of an earth tester. A typical earth tester has 4

terminals C1, C2, P1 and P2. The electodes are connected to the

tester in the order of C1, P1 and P2, C2. The handle of the tester is

rotated in case of manual one or the button is pressed (in case of

motorised tester) and the reading of the resistance is read on the

megger scale. The reading of meggar is used in calculating the soil

resistivity in Ohm-meters.

If R is the resistance measured then the

Specific Resistivity = 2 aR

where a= Distance between the electrodes

The design of earth mat is based on the results of earth resistivity

measured in the switchyard area. The earth resistivity is taken at about

15 places in switchyard and more particularly near shunt reactor,

transformer, Circuit Breaker and control room locations.

Prior to the testing of soil resistivity and earth resistance, site should

refer to the guidelines issued by the Operation Services Deptt. at

Corporate Centre. The operation manual of the testing instrument

available at site should also be referred.

3.5 Earthing Material Back to contents page

Following Table gives the typical size and materials required for

different earthing items in the substation:

Table -1: Typical sizes of materials used for Switchyard Earthing

Sl. No. Item Size Material1. Main Earthing Conductor to be buried

in ground (for earthed mat & earth

pipes)

40 mm dia Mild Steel rod

2. Conductor above ground & earthing

leads (for equipment)

75 x 12 mm

G.S. Flat

Galvanised Steel

3. Conductor above ground & earthing

leads (for columns & aux. Structures)

75x12 mm

G.S. Flat

Galvanised Steel

4. Earthing of indoor LT panels, Control

panels and out door marshalling

boxes, MOM boxes, junction boxes &

lighting panels etc.

50 x 6 mm

G.S. Flat

Galvanised Steel

5. Rod Earth Electrode 40 mm dia

3000 mm

long

Mild Steel

6. Pipe Earth Electrode (in treated earth

pit) as per IS.

40 mm dia

3000 mm

long

Galvanised Steel

7. Earthing for motors 25 x 3 mm

GS flat

Galvanised Steel

8. Earthing conductor along outdoor

cable trenches

50 x 6 mm

MS flat

Mild Steel

3.6 Earthing Conductor Layout Back to contents page

i) Earthing conductor in outdoor areas is buried at least 600 mm

below finished ground level or as specified.

ii) Wherever earthing conductor crosses cable trenches, underground

service ducts, pipes, tunnels, railway tracks etc. it is laid at

minimum 300 mm below these and be re-routed in case it fouls with

equipment/structure foundations etc.

iii) Tap-connections from the earthing grid to the equipment/structure

to be earthed are terminated on the earthing terminals of the

equipment/structure as per earthing details.

iv) Earthing conductors crossing the road is laid 300 mm below the

road or at greater depth to suit the site conditions.

v) Earthing conductors embedded in the concrete should have

approximately 50 mm concrete cover.

vi) Earth grid should be extended beyond 2000 mm from the

switchyard fencing towards out side.

vii) A minimum clearance of 1500 mm is maintained between the

earthing conductor and the control room building.

3.7 Equipment and Structure Earthing in Substation Back to contents page

i) Earthing pads are provided for the apparatus/equipments at

accessible position. The connection between earthing pads and

the earthing grid is made by two short earthing leads (one direct

and another through the support structure) free from kinks and

splices by 75 mm x 12 mm GS earth flat. The GS earth flat is

welded to a MS Rod riser which is connected to the earth mat in

ground.

ii) All steel/RCC columns, metallic stairs etc. are connected to the

nearby earthing grid conductor by two earthing leads. Electrical

continuity is ensured by bonding different sections of rails and

metallic stairs.

iii) Metallic pipes, conduits and cable tray sections for cable

installation are bonded to ensure electrical continuity and

connected to earthing conductors at regular interval. Apart from

intermediate connections, beginning points are also connected to

earthing system.

iv) A separate earthing conductor should be provided for earthing the

lighting fixtures, receptacles, switches, junction boxes, lighting

conduits etc.

v) A continuous ground conductor of 16 SWG GI wire is run all along

each conduit run and bonded at every 600 mm by not less than

two turns of the same size of wires. The conductor is connected

to each panel ground bus, all junction boxes, receptacles, lighting

fixtures etc.

vi) Railway tracks within switchyard are earthed at a spacing of 30 m

and also at both ends.

vii) 50 mm x 6 mm MS (or of specified size) flat runs on the top tier

and all along the cable trenches and the same is welded to each

of the racks. Further this flat is earthed at both ends at an

interval of 30 mtrs. The M.S. flat is finally painted with two coats

or Red oxide primer and two coats of Post Office red enamel paint

or of specified material.

viii) In isolator the base frame is connected to the earth mat.

The following Table-2 gives the various parts required to be earthed

alongwith their method of connection

Table:2 Details of Apparatus /Structures to be earthed in Switchyard

Sl. No. Apparatus Parts to beEarthed

Method of connection

1. Support of bushing

insulators, Lightning

Arrester, fuse, etc.

Device flange or

base plate

Earth terminal of

each pole of 3

phase Surge

Arrester

Connect the earthing bolt of the

device to station earthing system.

In the absence of earthing bolt or in

case of connection to non-

conducting structures, connect

device fastening bolts to earth

When the device is mounted on a

steel structure, weld the structure,

mounting the device flange; each

supporting structure of apparatus to

earthing mesh via separate

conductor2. Cabinets of control and

relay panels

Frameworks of

switchgear and

cabinets

Weld the framework of each

separately mounted board and

cabinet minimum at two points to

the earth conductor of earthing

system.3. High-voltage Circuit

Breakers

Operating

mechanism,

frame

Connect the earthing bolt on the

frame and to operating mechanism

of CB to earthing system4. Isolator Isolator base

(frame),

operating

mechanism

bedplate.

Weld the isolator base frame,

connect it to the bolt on operating

mechanism base plate and station

earth.

Provide an auxiliary earth mat of

600 mm x 600 mm of earth

conductors in the ground near the

earth switch and connect the both.5. Surge Arrester Lower earth

point

To be directly connected to the

earth mat.

6. Potential

Transformer/CVT

CVT tank. LV

neutral, LV

winding phase

lead (if

stipulated by the

designers)

Connect the transformer earthing

bolt to earthing system.

Connect LV neutral of phase lead

to case with flexible copper

conductor.7. Current Transformer Secondary

winding and me

tal case

Connect secondary winding to

earthing bolt on transformer case

with a flexible copper conductor,

the case being earthed in the same

way as support insulators.8. Power transformer Transformer

tank

Connect the earthing bolt on

transformer tank to station earth.

Connect the Neutral directly to two

dedicated earth pits.9. Fencing Alternate

Fencing portions

GS earth flat connects the fencing

to earth mat.10. Water tanks Lightning rods

provided over

the top of water

tank

GS earth flat connects the lightning

rods to earth mat.

11. Cable trays & supports Cable trays and

support

GS flat running near trays is welded

at a spacing of 750 mm and

connected to earth mat at about 30

m distance.12. Shunt Reactor Tank Same as in transformer. NGR is

also connected to two earth pits.

3.8 Jointing Back to contents page

i)Earthing connections with equipment earthing pads are bolted type. Two bolts are

provided for making each connection. Equipment bolted connections, after being

checked and tested are painted with anti-corrosive paint/compound of specified

material.

ii)Resistance of Joint should not be more than the resistance of the equivalent length

of the conductor.

iii)All ground connections are made by electric arc welding. All welded joints are

allowed to cool down gradually to atmospheric temperature before putting any load

on it. Artificial cooling is not allowed.

iv)Each earthing lead from the neutral of the power transformer/reactor is directly

connected to two pipe electrodes in treated earth pit (as per IS) which in turn, are

buried in Cement Concrete pit with a cast iron cover hinged to a cast iron frame to

have an access to the joints. All accessories associated with transformer/reactor like

cooling banks, radiators etc. are connected to the earthing grid at minimum two

points.

v)Earthing terminals of each lightning arrester & Capacitor Voltage Transformer is

directly connected to rod earth electrode which in turn is connected to station

earthing grid.

3.9 Measurement of Earth Resistance Back to contents page

Three electrode methods is used for measuring the earth resistance in

switchyard (Fig. 14). To measure the earth resistance both C1 and P1

terminals of megger could be connected to a spike that is driven in

ground and connected to earth mat whereas terminals P2 and C2 are

connected to the equidistant spikes driven in ground (not connected to

earth mat). The value of of R could be read in the scale with the

rotation of the handle of megger or press of a button. This will give the

value of earth resistance. The value as far as possible should be below

1 ohm. In case this value is high water should be sprinkled in the

earthing pits for improvement of earth resistance.

DO’S DON’TS&

SPECIAL PRECAUTIONS

3.10 Do’s Don’ts and Special PrecautionsBack to contents page

i) Metallic conduits should not be used as earth continuity conductor.

ii) Wherever earthing conductor crosses or runs along metallic

structures such as gas, water, steam conduits, etc. and steel

reinforcement in concrete it should be bonded to the same.

iii) Flexible earthing connectors should be provided for the moving

parts.

iv) Steel to copper connections should be brazed type and treated to

prevent moisture ingression.

v) Sheath and armour of single core power cables should be earthed

at switchgear end and equipment side.

vi) Contact surface of earthing pads for jointing free from scale, paint,

enamel, grease, rust or dirt.

vii) Earthing conductors or leads along their run on cable trench ladder,

columns, beams, walls etc. should be supported by suitable

welding/cleating at intervals of 750 mm/ as specified.

viii)Light poles, junction boxes on the poles, cable and cable

boxes/glands, lockout switches etc. are connected to the earthing

conductor running alongwith the supply cable which inturn is

connected to earthing grid conductor at a minimum two points

whether specifically shown or not

ix) Earthing conductor is generally buried 2000 mm outside the

switchyard fence. All the gates and every alternate post of the

fence is be connected to earthing grid.

x) Meggar used for measuring soil resistivity should be calibrated with

great accuracy. In case if an accurately calibrated meggar is not

available, 2 or 3 different meggars should be used to take same set

of readings.

xi) The earth resistivity should be taken in dry weather condition.

xii) For transformer & shunt reactor earthing, earth pits of 3-4 m depth

below the ground with 40 mm dia GI pipe & specified quantity of salt

and coke should be provided.

xiii)The earth resistance should also be measured after completion of

laying of earth mat and earth electrodes by the same 4 electrode

methods for complete system, individual earth pits & earth rod

electrodes.

xiv)The measured value of combined earth resistance should not be

more than 0.5 ohm.

xv) For earth electrodes and individual earth pits, this value can be upto

1 ohm.

xvi)In case these values are not being achieved water should be

poured in earth pits to bring the earth resistance within the specified

range.

CHECK FORMAT

3.11 Check Format Back to contents page

1. Proper unloading arrangement has been made at site

(Preferably with crane) to unload the material.

Yes/No

2. All items have been checked with the packing list, MICC,

Challans, GR etc.

Yes/No

3. After unloading the visual inspection of the materials has

been carried out along with the erection contractor.

Yes/No

4. Earthing material has been checked for dimensions and

quality .

Yes/No

5. The galvanization of steel (where GI steel is to be used) is

proper.

Yes/No

6. Earthing conductor is buried at least 600 mm below finished

ground level/ at specified level.

Yes/No

7. Earthing Conductor crossing the road is laid 300 mm below

the road or at greater depth depending on the site

conditions

Yes/No

8. Earthing conductor in outdoor areas is buried at least 600

mm below furnished ground level.

Yes/No

9. Earth grid has been extended beyond 2000 mm from the

switchyard fencing towards outside.

Yes/No

10 Earthing pads have been provided for the apparatus /

equipments at accessible position.

Yes/No

11 All steel/RCC columns, metallic stairs are connected to

nearby earthing grid conductor by two earthing leads.

Yes/No

12 Metallic pipes, conducts and cable tray sections for cable

installations are bonded & then connected to earthing

conductor at regular interval

Yes/No

13 Earthing of Lighting fixtures, receptacles, switches, junction

boxes lighting conduit has been done by a separate

earthing conductor.

Yes/No

14 Railway tracks within switchyard area has been earthed at a

spacing of 30m/specified distance and also at both the

ends.

Yes/No

15 Cable trays have been connected to earthing flat of 50 mm

x 6 mm/ specified sized earthing flat.

Yes/No

16 This earth flat is earthed at about 30m distance. Yes/No17 Bolted conditions of earthing with the equipments have

been checked and tested before painting with anti corrosive

paint.

Yes/No

18 For transformer and shunt reactor earthing, earth pits of 3-4

m depth with specified sized GI pipe & specified quantity of

salt and coke have been provided.

Yes/No

19 Sheath & armour for single core power cable have been

earthed at switchgear end.

Yes/No

20 All accessories in transformer and reactor like radiators

tank, cooling banks etc. are connected to the earthing grid

at minimum two points.

Yes/No

21 Megger used for measuring earth resistivity has been

calibrated with great accuracy

Yes/No

22 Earth resistance has been measured after laying the

earthmat.

Yes/No

23 4 electrode method has been applied to measure the earth

resistance

Yes/No

24 Measured value of earth resistance is within specified range Yes/No25 In case the values are not within the specified limit, water

has been poured in earth pits to bring the earth resistance

within the specified range

Yes/No

CHAPTER-4SWITCHYARD STRUCTURES

___________________________________________________________________________CHAPTER

FOUR___________________________________________________________________________

SWITCHYARD STRUCTURESBack to contents page

4.0 Introduction


Two types of structures are used in switchyard erection. These are

lattice type and pipe type structures. With both these type of structures,

supply of other components like washers, fasteners, foundation bolts

and other bolts & nuts is also linked up. Efforts should be made such

that a proper co-ordination is made in procuring these supplies and

structures so that erection work is not delayed due to non availability of

one or the other item. Various aspects right from the scope of work to

the erection of structures are described below.

4.1 Structure works in Substation Switchyard


The scope of structural work in switchyard generally includes receipt,

handling, storage and erection of all lattice/pipe structures, lightning

masts, beams as shown in structural arrangement drawings and lattice

support for gantry and various equipments like CT, CVT, LAs etc. The

structure supports also include the cap and base plates, stiffeners,

clamps, foundation bolts mounting stool and bolts, fixtures for

supporting operating mechanism boxes, control cabinet etc. It also

includes the fabrication, supply, painting, erection of angle supports

and embedding in cable trenches as per cable trench designs and

layout, no. plates, phase plates and danger plates.

4.2 Receipt of Material & Inspection


After receipt of all the materials at site, it should be inspected jointly

with the erection agency. This inspection is required to check the

materials received for their quantity, quality, correctness and

identification marks as per the delivery challan/ packing list etc. One

should go for checking the following :-

i) Despatch documents such as RR, LR, GR, MICC, Gate Pass,

Packing List etc.

ii) Quantity of materials received with the delivery challan, packing

list, BOQ and any shortages should be recorded.

iii) Identification marks should be checked from the MICC.

iv) Any physical damage should be brought to the notice of

supplier.

4.3 Storage


i) The erection agency is allowed to store the angle/pipe material

near the place where tower gantries are to be installed. All

angles and pipes are to be stacked properly in such a way that

retrieving of required materials is easy.

ii) Maintenance of proper stock registers by the erection agency is

to be checked regularly by duly counter signing the registers.

iii) Bolts/nuts, spring washers, pack washers (in bags) should be

stored in the allocated room/building meant for storage with the

proper tags depicting the size, quantity, code no., supplier name

etc.

iv) In case the store building is not ready, the material may be kept

tents with adequate security.

4.4 Erection


4.4.1 Erection of Gantry & Lattice Structures


i) The erection should be carried out as per the specified technical

instructions and approved drawings.

ii) Tolerances are established in the approved manufacture drawings

or as stipulated in the technical specifications. Necessary care

should be exercised in handling to avoid the distortion of structures,

the marring of finish or bending of tower members.

iii) The erection work is carried out manually (by built up or piece meal

method) using ginpoles/derricks. However, crane can be used for

this purpose.

iv) The members are kept on ground serially according to erection

sequence.

v) The erection progress from the bottom upwards.

vi) The cross braces of the first section which are already assembled

on the ground are raised one by one as a unit and bolted to the

already erected corner leg angles.

vii) For assembling the second section of the towers, gin poles are

placed one each on the top of the diagonally opposite corner legs.

These two poles are used for raising parts of second sections.

viii)This process is continued till the complete tower in gantry is

erected.

ix) The lattice structure are used for various equipment erection in the

switchyard like circuit breaker, current transformer, CVT and surge

arrester.

x) Proper care in horizontal levelling of these lattice structure is taken

by using water level/spirit level. Even dumpy level/theodolyte may

also be used for good accuracy.

xi) To maintain the proper level necessary shims are inserted in pipe

works.

xii) The beam erection work of tower is carried out at the ground by

assembling various members preferably in two parts.

xiii)The assembled beam is lifted either by crane or by chain pulley

block. Even winch machines can also be used for this purpose.

xiv)The assembled beam is lifted slowly and carefully.

xv) One side of the beam is tightened first with the gantry structure on

one side. For finer adjustments winch machines can be used. This

side of assembled beam is fixed to the tower by proper sized bolts,

nuts & washers.

xvi)All the support structure for various equipments should be levelled

horizontally with water/spirit levels.

4.4.2 Erection of Pipe Structure


i) The pipe structure are placed on the foundation bolts preferably by

cranes.

ii) During erection the top level of the pipe structure should be

maintained horizontal.

iii) This can be checked with the spirit level and shims can be used to

fill up the gap and to maintain the proper horizontal level.

iv) Necessary care is taken during pipe structure erection so that no

damage is caused to the threads of the foundation bolts.

v) The persons doing erection of pipe structure should use the safety

measures like helmets and safety belts etc.

4.3 Lightning Masts


Lightning masts are the highest angle iron structures in the switchyard.

These are designed in the switchyard keeping in view the approved

switchyard bays. The erection procedure of Lightning Masts is similar

to that of tower and gantries.

DO’S DON’TS&

SPECIAL PRECAUTIONS

4.4 Do’s, Don’ts and Special Precautions


During the erection of gantries/lattice structures/pipes following points

should be kept in mind.

i) As the supplies of lattice structure, washers, bolts and nuts, pipes

etc. is in the scope of different agencies, a co-ordinated follow up

should be maintained with the suppliers to the deliveries of these

items as per schedule. This will help in avoiding delays of erection

works due to non availability of one of these items.

ii) The lattice members, pipes etc. should be checked as per the BOQ

at site. The shortage or missed members in supplies should be

taken up with the suppliers rigorously. The erection work should be

started only after the structures are complete memberwise.

iii) Cranes should be used preferably for erection of pipe structure in

the switchyard.

iv) All safety procedures for erection work like use of safety helmets,

safety belts, use of guy wires etc. should be strictly adhered to

during structure erection works in the switchyard.

v) All the net/bolts should be tightened properly after the completion of

structure erection.

vi) Punching of bolts should be done.

vii) Any bend members and pipes should not be allowed and

straightaway rejected during supply stage.

viii)No hammering of members should be allowed to match the holes

during erection work.

ix) 2-3 threads of bolts should be exposed after tightening the nuts for

punching purpose.

x) Proper sized/bolts/nuts and pack washers should be used in

erection.

xi) After the completion of tower erection, proper tightening is to be

done. Before carrying out the final punching it must be ensured that

proper sized spring washers are provided.

xii) During erection, it should be seen that brazings should be properly

erected i.e., outer face of the member should always be at top so

that water does not stager on the members (water gate). Also,

members should not be over tensioned while carrying out the

erection.

xiii)Proper lifting arrangement of 4-5 MT capacity should be used

during erection works.

xiv)Proper sized spanners (box and ring type) as well as DE spanners

should be used.

xv) Poly-propylene ropes of 18/20/25 mm dia of about 100 m/as per

requirement length each may be used. The ropes should be

checked before use so as to avoid any breakage during works.

xvi)Steel rope of 3/8” dia of required length should be used with winch

machine.

xvii)D-shackles of 2 to 20 MT of different sizes should be used.

xviii)Single sheave and double sheave pulleys should not be less than

5 MT capacity. These should be checked for their smooth rotation

and locked during use on works.

xix)The verticality of different lattice structures should not be less than

the specified tolerance of 1 in 360.

xx) Proper punching of bolts/nuts is to be done on the various

structures.

CHECK FORMAT

4.5 Check Format



Challans GR etc.

Yes/No

2. After unloading the visual inspection of the angles/members

has been carried out for any bend/ damage.

Yes/No

3. All the members have been stacked properly in store. Yes/No4. Angles have been checked for size/dimensions, galvanization

and bend etc.

Yes/No

5. Required quantities of washers, fasteners, foundation bolts &

other bolts/nuts are available before starting the structure

erection at site.

Yes/No

6. All pipes have been checked and found straight w.o. any bends

or damage.

Yes/No

7. Bolts/nuts/spring, pack washers are stored in the closed room

(in bags).

Yes/No

8. Proper tags depicting the size, quantity code no. and supplier

name etc. have been written/inscripted on the tags tied on the

bags.

Yes/No

9. During structure erection proper safety measures like helmets,

safety bolts, ropes etc. are being used by the working

personnel.

Yes/No

10. All lattice members are available (as per drawings) before start

of erection.

Yes/No

11. Proper care in horizontal levelling of lattice structure for

equipments is taken by using water/spirit level.

Yes/No

12. To maintain proper level, shims have been inserted in pipe

works.

Yes/No

13. Assembled beam (of gantry structure) is being lifted with crane

for erection with proper safety.

Yes/No

14. Tightening and punching of bolts has been done properly. Yes/No15. Hammering of members has been disallowed during erection at

site.

Yes/No

16. 2-3 threads of bolts are exposed out after tightening the nuts for

punching purpose.

Yes/No

17. Proper sized bolts/nuts and pack washers are used in tower

erections.

Yes/No

18. Verticality of tower is within the safe tolerance of 1 in 360. Yes/No

CHAPTER-5BUSPOST INSULATORS & BUSBARS

___________________________________________________________________________

CHAPTER FIVE

___________________________________________________________________________

BUS POST INSULATORS & BUS BARSBack to contents page


The substation busbars can be broadly classified in the following three

categories:

i) Outdoor Rigid Tubular Busbars

ii) Outdoor flexible ACSR aluminium alloy busbars

iii) Indoor busbars

The busbars are designed to carry certain normal current continuously.

The cross-section of conductors is designed on the basis of rated

normal current and permissible temperature rise. The value of cross

section so obtained is verified for temperature rise under short-time

short-circuit current.

The busbar conductors are supported on post insulators or strain

insulators. The insulators experience electro-dynamic forces during

short circuit currents. These forces are maximum at the instant of peak

of first major current loop. These forces produce bending moment on

separated insulators. The spacing between adjacent insulators is

decided on the basis of bending moment per metre and strength of

insulators.

5.1 Steps in Busbar Design Back to contents page

The busbar design is carried out in the following steps:

i) Choice of cross-section of conductor based on required normal

current, given ambient temperature and specified permissible

temperature rise.

ii) Calculation of temperature rise under short time current to see that

it is in safe limits.

iii) Calculation of electro-dynamic forces per metre for given short

circuit current.

iv) Calculation of choice of support insulators on the basis of bending

moment withstand value.

v) Calculation of span of support insulators on the basis of the force,

bending strength of insulators and factor of safety.

vi) Design of insulator system, phase to phase clearance, phase to

ground clearance and creepage.

vii) Design of support structures.

viii)Design of clamps and connectors, flexible joints.

5.2 Forms of Busbars Back to contents page

Busbars of Outdoor Switchyard are in the following forms:

ACSR conductors supported at each end on strain insulators.

Tubular Aluminium Conductors supported on post insulators

made of porcelain. These are either welded to get extended

lengths.

Busbars for Indoor Switchgear are in the form of aluminium or

copper flats. These are supported on epoxy cast insulators.

5.2.1 ACSR Back to contents page

ACSR conductor to be used for busbars is supported on insulators. As

most of the equipments can be installed below the flexible bus, land

requirements are also less. The cost of this scheme is lower due to

less no. of support structures.5.2.2 Aluminium


Aluminium is used for busbars in indoor and outdoor switchgear.

Aluminium and aluminium castings (5 to 12% silicon) are used in

busbar. Aluminium is used in the form of strips /rectangular bars for

busbar application. While using aluminium for busbars, the difficulties

arise due to the following aspects:

i) Higher resistivity, hence associated problems of temperature rise.

ii) Lower tensile strength than copper.

iii) Lower thermal conductivity than copper.

iv) Higher coefficient of linear expansion than copper.

v) Higher joint resistance and associated problems about joining.

vi) Special welding techniques are necessary.

5.3 Configuration of Busbars in Outdoor Substation Back to contents page

The conductors of a busbars systems in an outdoor substation are of

the following two types:

i) Rigid aluminium tubular bus conductors supported on post

insulators

ii) Flexible ACSR supported on strain insulators. The conductors of

three phases of each bus are placed in horizontal configuration.

Table 1: Comparison between Rigid Bus System and Flexible Bus System

Feature Rigid Bus System Flexible Bus SystemCost Higher because of higher

conductor cost, post insulator

cost

Lower

Land Area

requirement

Larger Lower. Most of the

equipment installed below

the flexible busNumber of support

structures

- More numbers

- Simple

- Amount of steel lesser

- Less numbers

- Complex

5.4 Receipt and Inspection of Material at site Back to contents page

i) The items should be checked with the packing list, MICC, Challans

GR etc.

ii) In case of any discrepancy from the above documents/LOA the

same may be intimated to the manufacturer at the earliest.

iii) Any type of damage to the panels during transportation or any

missing items should also be brought to the notice of the panel

supplier.

iv) All materials and packages are to be carefully opened and verified

for damages and shortages, if any. These shortcomings have to be

properly intimated to the manufacturer as well as to the Insurance

authorities as the case may be.

v) Handling of large crates should be handled by crane carefully.

vi) All items should be stored on ramps/platforms, free from water

logging.

vii) BPIs are to be stored separately to avoid breakages.

5.5 Bus Post Insulators Back to contents page

Post type consist of a porcelain part permanently secured in a metal

base to be mounted on the supporting structures.

They are capable of being mounted upright. They are designed to

withstand any shocks to which they may be subjected to by the

operation of the associated equipment.

Porcelain used is homogeneous, free from lamination, cavities and

other flaws or imperfections that might affect the mechanical or

dielectric quality and thoroughly vitrified, tough and impervious to

moisture. Glazing of the porcelain is of uniform brown in colour, free

from blisters, burrs and other similar defects.

The insulator have alternate long and short sheds with aerodynamic

profile.

The design of the insulators should be such that stresses due to

expansion and contraction in any part of the insulator should not

lead to deterioration in Bus Post insulators

i) Every bolt should be provided with a steel washer under the nut

so that part of the threaded portion of the bolts is within the

thickness of the parts bolted together.

ii) Flat washer should be circular of a diameter 2.5 times that of

bolt and of suitable thickness. Where bolt heads/nuts bear upon

the levelled surfaces they are provided with square tapered

washers of suitable thickness to afford a seating square with the

axis of the bolt.

iii) All bolts and nuts should be made up of steel with well formed

hexagonal heads forged from the solid and hot dip galvanised.

The nuts should be good fit on the bolts and two clear threads

should show through the nut when it has been finally tightened

up.

5.5.1 Technical Parameters of typical Bus Post Insulators are Back to contents page

a) Type Solid core Solid core

b) Voltage class (kV) 420 245

c) Dry and wet one minute 680 460

power frequency withstand

voltage, Kv (rms)

d) Dry lightning impulse + 1425 + 1050

withstand voltagee) Wet switching surge + 1050 -

withstand voltage (kVp)

f) Max. radio interference 1000 1000

voltage (in microvolts)

at voltage of 305 kV (rms)

and 156 (rms) for 400 kV &

220 kV respectively

between phase to ground.

g) Corona extinction voltage 320 (Min.) 156 (Min.)

(kV rms)

h) Total minimum cantilever 800 800

strength (Kg)

i) Minimum torsional moment As per IEC-273

j) Total height of insulator (mm) 3650 2300

k) P.C.D

Top (mm) 127 127

Bottom (mm) 300 254

l) No. of bolts

Top 4 4

Bottom 8 8

m) Diameter of bolt/holes (mm)

Top M16 M16

Bottom dia 18 18

n) Pollution level as per Heavy(III) Heavy(III)

IEC-815

o) Minimum total creepage 10500 6125

distance for Heavy

Pollution (mm)

5.6 Erection of Aluminium Bus Bar Back to contents page

i) Before erection of the tube, it is to be checked for any scratches. If

any scratches are observed, they are to be repaired by means of

smooth file and emery paper.

ii) As Aluminium tube is soft material it is to be handled carefully to

avoid damages and scratches.

iii) The tube can be erected by means of crane or by means of a

derrick.

iv) Only polypropylene ropes are to be used to tie the tube while lifting.

v) After erection of the Aluminium tube it is to be checked that it rests

on all the BPI clamps (rigid/sliding/expansion) properly. If not,

necessary adjustments may be made by providing shims between

the clamp and the BPI.

vi) During erection of the tube care should be taken such that the tube

should be in perfect straight line and perfect level. The BPI clamps

suitable for Aluminium tube (rigid/sliding/expansion types) are

erected as per the erection key diagram.

5.6.1 Bending Procedure of Aluminium Tube During Erection: Back to contents page

Following bending procedure should be adopted during bending of the

Aluminium tube while bus bar erection

i) Wherever required the tube is bent suitably into a Z shape.

ii) Suitable tube bending machine is to be made use of.

iii) The tube bend should not be bent more than 45o.

iv) To ensure the circular cross section of the tube at the place of

bending the tube should be filled with smooth sand, well compacted

throughout the length of the tube and the ends should be plugged..

v) Care should be taken such that the tube is in one plane only even

after bending.

5.6.2 Welding of Aluminium Tube:


i) Aluminium tube welding is done at erection site only by a qualified

and approved welder.

ii) Tube ends to be welded are cut neatly and precisely in shape.

iii) Both the tubes to be welded are kept in a plane and in the same

axis.

iv) Plane of the cut edge is to be exactly perpendicular to the plane

of longitudinal section of the tube.

v) The edge is to be made by grinding to the shape.

vi) Tube centring spacer is inserted in between them.

vii) Suitable welding sleeves of specified length for the above tube,

specially supplied for the purpose of tube welding is kept within

the tube, equally distributed in length among the tubes.

viii) After putting the pieces and welding sleeve in position 12 mm dia

holes are to be drilled at 100 mm intervals.

ix) Aluminium rods of specified length and dia with one end counter

shunk are inserted through these holes.

x) To accommodate the counter shunk aluminium rod the counter

shunk shape is drilled in the Aluminium Tube only.

xi) After positioning the tubes, welding sleeve and the Aluminium

rods in position the welding is to be taken up.

xii) The counter shunk Aluminium rods also are to be welded to the

tube.

xiii) Milli volt drop tests for testing the joints should be performed in

the field.

xiv) All other tests as given in the FQP should also be performed.

xv) If any of the joints are not successful in the test, those joints are

to be re-done.

5.7 Welding Procedure and Welder’s Qualifications Back to contents page

The erection contractor is supposed to get the Welding Procedure and

Welder’s /Welding Operator’s Qualifications approved from the

Corporate QA deptt. (in the enclosed proforma at Annexure-I and

Annexure-II) before commencement of the Aluminium welding of the

bus at site.

DO’S DON’TS&

SPECIAL PRECAUTIONS

5.8 Do’s, Don’ts and Special PrecautionsBack to contents page

i)In Aluminium tube the welding joint should not be at the centre. It

should be between support and 1/3 distance of the span.

ii)Dust free atmosphere is to be maintained at the place of welding.

iii)Check that proper alignment for complete aluminium tube is

achieved and verified before any welding is done.

iv)The welds in the Aluminium tube should be kept to the minimum and

there should not be more than one joint in the tube in any span length.

v)No inflammable material should be present around the work spot.

vi)While welding work is under progress, ensure the argon gas flow

along with the arc and also as long as the weld metal is red hot. This is

to prevent oxidation of the weld metal because of exposure to oxygen

in the atmosphere.

vii)The shed profile should meet requirements of IEC-88815 for the

specified pollution level.

viii) Welding of Aluminium tube at site should be done by adopting an

approved welding procedure and employing a qualified welder.

ix) Welders employed for Aluminium tube welding should be

experienced one in the field.

x)Corona bells should be provided wherever the bus extends beyond

the clamps and on free ends, for sealing the ends of the tubular

conductor against rain and moisture and to reduce the electrostatic

discharge loss at the end points.


1. Proper unloading arrangement has been made at site (Preferably

with crane) to unload the packages.

Yes/No

2. All items have been checked with the packing list, MICC, Challans

GR etc.

Yes/No

3. After unloading the visual inspection of the packings has been

carried out along with the erection contractor and preferably with

the manufacturer of the equipment.

Yes/No

4. Any type of damage to the equipments/components during

transportation or any missing items has been brought to the

notice of the supplier.

Yes/No

5. Porcelain of BPI is free from lamination, cavities and other flaws

or imperfections.

Yes/No

6. Glazing of the Porcelain is uniform and free from blisters, burrs

and other defects.

Yes/No

7. Every bolt has been provided with a steel washer under the nut. Yes/No8. Packed washers of suitable size and thickness have been

provided.

Yes/No

9. Aluminium tube welding is being done by a qualified welder. Yes/No10. Aluminium tube welding is done as per approved welding

procedure.

Yes/No

11. Dust free atmosphere has been maintained at the place of

welding.

Yes/No

12. No inflammable material is present around the work spot Yes/No13. Care is taken so that not more than one joint is provided in one

span length

Yes/No

14. Aluminium tube has been checked for any scratches Yes/No15. In case of any scratches these have been repaired by mean of

smooth file and emery paper.

Yes/No

16. Only polypropylene rope is being used for Aluminium Tube

erection.

Yes/No

17. The tube is in the straight line and perfectly levelled. Yes/No18. BPI clamps for holding Aluminium tube have been erected as per

erection key diagram.

Yes/No

CHECK FORMAT

19. Suitable bending machine is used for bending purpose. Yes/No20. Care has been taken to maintain circular cross section of tube at

the place of bending by filling tube with smooth sand, well

compacted in the entire length & ends plugged.

Yes/No

21. Care has been taken so that pipe is in one plane after bending. Yes/No

Annexure - IQW-482 WELDING PROCEDURE SPECIFICATION (WPS)

SECTION IX, ASME-1986_____________________________________________________________

Joints (QW-402)

Joint Design :

Backing :

_____________________________________________________________

Base Metals (QW-403)

P.No. 23, Group No. SB221 to P No. 23, Group No. SB 221

Specification type and grade :

Pipe dia range :

Thickness Range :

_____________________________________________________________

Filler Metals (QW-404)

F. No. 23

Specification No. : (SFA) 5.10

AWS No. ER 4043

Size of filler metals :

_____________________________________________________________

_____________________________________________________________

Positions (QW-405)

Position of groove :

Welding progression :

_____________________________________________________________

Preheat (QW-406)

Preheat temperature min.

Interpass temperature max.

Preheat maintenance

_____________________________________________________________

Post weld heat treatment (QW-407)

Temperature range

Time range

____________________________________________________________

Gas (QW-408)

Shielding gas

Percent composition (mixture)

Flow rate

Gas backing

Trailing Shielding gas composition

_____________________________________________________________

_____________________________________________________________

Electrical characteristics

Current AC or DC

Amps (Range)

Tungston electrode size and type

Mode of metal transfer for GMAW

Electrode wire feed speed range

_____________________________________________________________

Technique (QW-410)

String or weave bead

Orifice or gas cup size

Initial and interpass cleaning

Method of back gauging

Oscillation

Contact tube to work distance

Multiple or single pass (per side)

Multiple or single electrode

Travel Speed (Range)

Peening

Other

_________________________________________________________________

WeldOthersLayer

Process Filler Class Metal dia Current

TypePolar

AmpRange

VoltageRange

Travel Speed

Annexure - IIDATA - FORMS

QW-484 SUGGESTED FORMAT FOR MANUFACTURER’S RECORD OFWELDER OR WELDING

OPERATOR QUALIFICATION TESTSWelder Name _________________ Check No. __________ Stamp No. _______

Welding Process __________________ Type ______________________________

In accordance with Welding Procedure Specification (WPS) ___________________

Backing (QW-402) ___________________________

Material (QW-403) Spec. ______ To ______ of P.No. ______ to P.No. ________

Thickness _______ Dia _______

Filter Metal (QW-404) Spec. No. _________ Glass No. _________F No. _________

Other _____________________________

Position (QW-405) (1G, 2G, 6G) ________________________________________

Gas (QW 408) Type _______________ % Composition _____________________

Electrical Characteristics (QW 409) Current _________________ Polarity _______

Weld Progression (QW-410) __________________________________________

Other _____________________________________________________

For Information Only

Filler Metal Diameter and Trade Name _________________________

Submerged Arc Flux Trade Name _________________________

Gas Metal Arc Welding Shield Gas Trade Name _______________________

Guided Bend Test Results QW-462.2(a). QW-463.2(a),QW-462.3(b)Type and Fig No.

Radiography Test for (QW 304 & QW-305)For alternative ____________ in above welds by radiography

Radiographic Results _________________________

Filler Weld Test Results _____________________62.4(a), QW-462 4(b)

Fracture Test (describe the location, nature _________________________

Length and Percent of _________________ inches %

Macro Test-Fusion

Appearance -Fillet Size________________________ in Convexity in or

Concavity _________ in ______________

Test conducted by ____________________ Laboratory - Test No. _______

We certify that the statements in this record are correct and that the test welds were

prepared, welded and tested required by the Code.)

NOTE: Any essential variables in addition to those above shall be recorded.

CHAPTER-6STRINGING SWITCHYARD

___________________________________________________________________________

CHAPTER SIX

___________________________________________________________________________

STRINGING IN SWITCHYARD


6.0 Introduction


In switchyard overhead stringing work is done between the gantries

and from the last tower on the lines to the first gantry structure. The

overhead stringing in 400 KV yard is done with twin ACSR moose

conductor. Erection of equipments can be started only after the

overhead stringing has been completed in the gantries of the

switchyard. The various outdoor equipments are connected with

overhead conductors by jumpers/droppers with suitable clamps.

Stringing is done manually in the switchyard, however, winch

machines may be used for final sag.

6.1 Pre- Stringing checks


Though stringing work in switchyard is of small nature as compared to

a transmission line even then the site should take care of the following

before the stringing work starts at site.

i) Before starting and also during stringing works the condition of

conductor should be checked for any damage or scratches to the

aluminium strands of conductor.

ii) The glass/porcelain portion of insulators should be checked for any

cracks

iii) Insulators should be clean from dust or other foreign materials.

iv) Conductor should not be allowed to lie or rub on the ground during

paying/pulling.

v) Nuts and bolts of all gantry structure should be checked and the

tower members should be complete in all respect.

6.2 Stringing


The process of manual stringing of moose conductor at site involves

the following steps :

i) Conductor is pulled between the gantries and strung on the

suspension on insulator strings.

ii) The final sagging is done by using winch machines. The winch

machines are connected to the leg of the towers/gantries.

iii) Final adjustment of conductor is done upto the desired point that

point by moving the conductor through winch machines and the

conductor is cut at the desired length.

iv) Dead end joint by compression machines is provided at the end of

the conductor with the dead end cone compressed with

compression machine.

v) Conductor is strung at the end with the double tension fitting.

vi) On suspension structure the conductor is strung through

suspension clamps.

vii) Spacers are provided between twin conductors after final sag is

completed.

6.3 T & P and Materials used for Stringing


The following Tools and Plants and Line material is required while

stringing in substation switchyard.

Single sheave pulley (open type) - 4 Nos.

Double sheave pulley - 2 Nos.

Hydraulic/manual compression

machine of 100T capacity with die sets - 1 No.

Winch machine 10T capacity - 1 No.

Come along Clamp(Bolted/Automatic - 6 Nos.

Wire Cutter - 1 No.

Poly-propylene rope (25 mm dia) - 100 m or as

desired

D -Shackle - 8 nos.fs

Wire slings of required length - 16 mm dia

Spanners, round/flat files Screw driver, - 1 set

flat files, steel tape, Hecksaw frame each

& blades / as per reqmt.

ACSR moose conductor - As per

reqmt.

Single suspension fittings - - do

-

Double tension fittings - - do

-

120 kN porcelain/glass insulators

for suspension fitting - - do

-

160 kN porcelain/glass insulators

for tension fitting - -

do -

Spacers

(Bundle spaces and/or Rigid spacers) - -

do -

DO’S DON’TS&

SPECIAL PRECAUTIONS

6.4 Do’s Dont’s and Special Precautions


i) Conductor during stringing should not be allowed to drag on

ground. For this purpose wooden planks or ground rollers should

be used to avoid any damage to the conductor.

ii) Insulator string should be pulled in such a way that it does not

drag/entangle with the tower members causing any damage.

iii) Adequate safety precautions should be taken by the personnel

working on the towers/ground. They should wear safety helmets

and use safety belts whole working on towers/structures. Workers

and supervisory staff working on ground should wear the safety

helmets.

iv) Conductor should be checked constantly as it is unwound from

conductor drum for any broken, damaged or loose strand. In case if

any major defect is noticed the defective conductor has to be

removed.

v) Marking of conductor should be done correctly after adjusting

length of tension fitting.

vi) Conductor should be cut at the marked point and dead end joint

be provided.

vii) Sag should be checked by sighting through the theodolite placed

on ground near the tower. Any mismatch should be corrected by

using sag adjustment plate in tension fitting.

viii)Immediate medical care should be provided to workmen met with

an accident. First Aid Box should be available at stringing site.

ix) Insulators should be completely cleaned with soft and clean cloth.

x) It should be verified that there is no crack or any other damage to

insulators.

xi) It is very important to ensure that ‘R’ clips in insulator caps are

fixed properly. This is a security measure to avoid disconnection of

insulator discs.

xii) Necessary precautions should be taken so that no damage to

insulators is caused during hoisting. In case of any damage, the

same needs to be replaced.

xiii)All hardware fittings should be provided as per approved drawings.

xiv)It should be verified that all nuts and bolts are tightened properly.

xv) It should be ensured that all the necessary security pins (split pins)

are fixed properly.

xvi)Conductor should be rejected in case it is found to contain any

broken, damaged or loose strands.

xvii)Proper arrangements should be made to avoid rubbing of

conductors on ground/hard surfaces by providing wooden planks.

xviii)Subconductors of each phase should be simultaneously tightened

by winch machine fixed on tower leg until the desired final sag is

achieved.

xix)Marking of conductor should be done correctly after adjusting

length of tension fittings.

xx) Conductor should be cut at the marked point and dead end joint be

provided with adequate compressive strength.

xxi)Spacers should be provided as per approved placement chart.

xxii)Length of jumper should be carefully checked such that it is in

parabolic shape and jumper drop is as per approved drawing.

Length of jumpers of sub-conductors of a bundle should be properly

checked so that jumper spacers lie in horizontal position as far as

possible.

xxiii)All nuts and bolts of jumper fittings should be properly tightened.

This is very essential to ensure tightness of jumpers to avoid hot

spot and melting in future.

xxiv)Jumper spacers should be provided as per technical specification

and approved drawings.

xxv)No damaged component of any hardware fitting should be used on

works.

xxvi)Sag mismatch should be within permissible limits.

xxvii)All fittings provided should be as per specification and approved

drawings. All necessary details like make, dimension, size and

specifications of these fittings should be recorded separately in

register for tractability in future.

xxviii)Jumpers/drops should be tightened properly. Live metal

clearance should be maintained as per specification.

xxix)Insulators should be cleaned with soft cloth. Glazing should be

proper and there should be no crack or white spot on its surface.

xxx)‘R’ Clips in insulators should be fitted properly.

xxxi) All Nuts/Bolts in fittings should be tightened properly.

xxxii)All components of fittings should be completely provided as per

approved drawings.

xxxiii)In case of Tension fitting dead end joint dimensions before and

after compression should be checked and recorded.

xxxiv)All components of spacers/jumper spacers should be provided as

per approved drawings.

6.5 Check Format


1. Towers are tightened properly and all the members, Nut/Bolts

are complete in no. and size.

Yes/No

2. All Line materials, tested T & P, safety equipments and

relevant drawings are available for stringing.

Yes/No

3. Conductor is checked continuously during stringing in

switchyard. Damaged portion, if any, is removed.

Yes/No

4. Proper arrangements are made to avoid rubbing of conductor

on ground/hard surfaces.

Yes/No

5. Sag is measured correctly at prevailing temperature. Details

are recorded.

Yes/No

6. After measuring sag, marking/cutting of Earthwire/ conductor is

done correctly to fix dead end joint.

Yes/No

7. Conductor, insulators and other hardware fittings are available

at site before starting the overhead stringing.

Yes/No

8. Insulators and other hardware fittings have been cleaned

properly before erection

Yes/No

9. All fittings have been assembled at ground and all components

are OK.

Yes/No

10. All components of fittings have been checked up for

dimensions and make as per the manufacturer’s drawings

Yes/No

11. Insulators have been checked for any cracks/damage and care

has been taken that insulators are not broken during lifting.

Yes/No

12. Care has been taken so that conductor while pulling is not

damaged.

Yes/No

13. Proper sag and tension have been maintained as per the day

temperature and sag tension chart

Yes/No

CHECK FORMAT

14. Subconductors of each phase are being tightened

simultaneously by winch machine & to achieve the desired

sag.

Yes/No

15. All nuts & bolts of jumper fittings have been tightened properly. Yes/No16. Jumper spacers have been provided. Yes/No17. Spacers have been provided as per the spacer placement

chart.

Yes/No

18. Care has been taken to avoid any overtensioning. Yes/No19. R. Clips of the insulators in insulator string have been properly

provided.

Yes/No

20. In both suspension and double tension fitting the split pin have

been splitted properly.

Yes/No

21. Length of jumpers has been measured properly to give it a

parabolic shape.

Yes/No

22. In case of tension fitting dead end joint dimensions before &

after the compression are checked and recorded.

Yes/No

23. Jumpers are tightened properly. Live metal clearance have

been maintained as per specification.

Yes/No

CHAPTER-7SURGE ARRESTER

___________________________________________________________________CHAPTER

SEVEN

SURGE ARRESTERBack to contents page


Surge Arrester is a device designed to protect electrical equipments

from high voltage surges and to limit the duration and amplitude of the

follow current. Surge arresters are used to protect Power System

Installations and equipments against lightning overvoltages also.

Generally arresters are connected in parallel with the equipment to be

protected, typically between phase and earth for three phase

installations.

The main element of a surge arrester is the ‘Non-Linear Resistor’, the

part of the arrester which offers a low resistance to the flow of

discharge current thus limiting the voltage across the arrester terminals

and high resistance to power frequency voltage, thus limiting the

magnitude of follow current.

There are 2 types of designs available for EHV Surge-Arrester. These

are Conventional gapped Surge-Arrester (Value Type) and Metal Oxide

Surge-Arrester.

7.1Conventional Gapped Lightning Arrester (Valve Type Arrester) Back to contents page

In a substation the Surge Arrester is connected between line and earth.

It is the first apparatus as seen from the overhead transmission line

entering in the switchyard. It consists of resistor elements in series with

gap elements offer non-linear resistance such that for normal

frequency power system voltages the resistance is high however, for

discharge currents the resistance is low. The gap units consist of air

gaps of appropriate length. During normal voltage4s the lightning

arrester does not conduct. When a surge-wave travelling along the

Overhead line comes to the arrester, the gap breaks down. The

resistance offered being low the surge is diverted to the earth. After a

few micro seconds the surge vanishes and normal power frequency

voltage is set up across the arrester. The resistance offered by

resistors to this voltage is very high. Therefore, are current reduces

and voltage across the gap is no more sufficient to maintain the arc.

Therefore, the current flowing to the earth is automatically interrupted

and normal condition is restored. The high voltage surge is discharged

to earth. Hence the insulation of equipment connected to the line is

protected.

7.2Metal Oxide Lightning Arresters Back to contents page

The metal oxide arresters without spark gaps consist of an active part

which is a highly non linear ceramic resistor made of essentially Zinc

Oxide. Fine Zinc Oxide crystals are surrounded by other metal oxides

(additives). Such microstructures render extreme non-linear

characteristics to these ceramic resistors.

In the operating characteristic of Surge Arrester the current axis is in

logarithmic scale. The current increases by 107 orders of magnitude

when the voltage across element doubles. This special characteristics

is the heart of protection technology in this type of Surge Arrester.

The lower linear part ‘A’ is temperature dependant and exhibits a

negative temperature coefficient. The arrester is designed in such a

way that the applied operating voltage gets located around point ‘O’.

This results in a continuous resistive curent of few micro amps flowing

through the resistor elements. Under over voltage condition, the

voltage increases and shifts operating pont momentarily for

overvoltage duration to point near ‘B’. This results in a resistive current

of few milli-Amperes flowing through the resistor elements. As soon as

the overvoltage disappears the operating point shifts back to ‘O’. In the

event of transient switching or lightning vervoltages, the operating point

will shift to portion ‘C’. For the transient of a few micro seconds it will

draw current in the range of 5/10 k Amps. In the event of very high

lightning current of the order of 40 to 100 k Amps peak, the operating

point will shift to portion ’D’. However, on expiry of transient of few milli

seconds the operating point will come back to point ‘O’.

Thus the operating point of these arresters is normally located at point

‘O’ called Maximum Continuous Operating Voltage (MCOV) and the

point ‘B’ of the Fig. (5) indicates approximately the rated voltage of

arrester. The arrester can stay at point ‘O’ i.e., MCOV, all long its life

but can stay at point ‘B’ (fault condition), i.e. Rated Voltage, for only 10

seconds (it is presumed that system breakers will operate to isolate the

fault within 2 seconds). The energy that gets dissipated, I.e. (I2R)

during continuous or overvoltage condition decides the size (dia) of

ZnO resistor element. These are classified as different classes

depending upon the energy handling capabilities. Higher class

corresponds to higher energy capability.

7.3 Packing, Transport, Handling And StorageBack to contents page

(i) Las are packed vertically on sturdy wooden case. For reasons of fragile

porcelain, care should be taken while unpacking, handling and installation

so as to avoid impact with hard surface.

(ii) Immediately on receipt, inspect the cases for signs of transhipment or

physical damages packings. In case of any damage matter should be

reported to insurance company as well as the manufacturer for guidance.

(iii) At site the Surge Arrester should e stored in the original packing case and it

should also be ensured that boxes are kept in the original vertical condition.

(iv) While taking out of the cases too, Arrester units should be placed in upright

position, the porcelain sheds facing down.

(v) As LAs are assembled in controlled condition, no attempt should be made at

site to open or repair the arrester without consultation of the manufacturer.

(vi) It is recommended to use nylon ropes for handling the arrester at site.

7.4 Installation


i) LAs are mounted on sturdy structure.

(ii) Mounting plate of structure top should be regular and horizontal.

(iii) Check the level with a Spirit Level before mounting.

(iv) Clean the porcelain surface of insulators.

(v) Measure resistance preferably by 5 kV meggar. The insulation

resistance should be more than 1000 M Ohms.

7.5 Installation of Single Unit Arrester


(i) Fix base plate with 4 bolts (if it was not already fixed) to LA bottom.

(ii) Base insulators should be placed loosely on the mounting plate of structure.

(iii) Fix the Surge Counter mounting bracket alongwith one of the base insulator

to the structure.

(iv) Lift the arrester vertically up as shown in figure.

(v) Lower the Arrester unit and use base insulator stud \ bolt to guide it in place.

(vi) Fix the Arrester in position.

(vii) Fix Surge Counter on the Surge Counter Bracket.

(viii) Connect the stud at the back of Surge Counter to base plate by the

connecting link.

(ix) When surge counter is not in use, base plate should be positively connected

to earth.

7.6 Installation of Multi-Stack Arrester


(i) Fix base plate to LA bottom (if not fixed already)

(ii) Loosen and remove 4 bolts from top of the top units.

(iii) Fix the corona ring to the top of the top unit / middle unit using

the same bolts.

(iv) Loosen and remove 4 bolts from top of the bottom unit (& Middle

unit in case of 3 stack LAs).

(v) Lift the Top unit and engage 4 studs at the bottom.

(vi) Lower the top unit to the top of bottom unit (or middle unit in

case of 3 stack LAs) by guiding the stud and keeping

intermediate plate in between.

(vii) Fix the units in place. (In case of 3 stack LAs fix the top & middle

unit to bottom unit as described above.)

(viii) Keep the base insulator loosely on the top of structure.

(ix) Lift the LA (interconnected) and lower the structure top by

guiding through the base insulator bolts.

(x) Fix the Surge Counter mounting bracket with one of the bolts.

(xi) Surge monitor is connected to the main earth mat in the

substation.

(xii) Ensure that structure is earthed with the earth mat in the

substation.

(xiii) Fix the LA and secure in position by the 4 bolts.

(xiv) Fix surge counter on the bracket and connect the stud at the

back of the surge counter to the base plate.

(xv) When surge counter is not in use, base plate should be

positively connected to earth.

(xvi) Connection of jumper to the LA, CVT can be made through T

clamp or P G clamp or directly connected to the overhead

conductor.

DO’S DON’TS&

SPECIAL PRECAUTIONS

7.7 Do’s, Don’ts & Special Precautions


(i) Slack span stringing from dead end tower to the gantry should

be completed before taking up of the erection of line Arrester.

(ii) Surge monitors of each phase is to be checked for any damage.

(iii) The IR value of each stack is to be measured.

(iv) Use of flexible copper strips between the bushings and earth

strips should be preferred.

(v) Proper care to prevent any damage to the surge bushing should

be taken.

(vi) Insulators should be cleaned before erection at site.

(vii) Terminal connectors should be tightened to proper torque.

(viii) Surge monitor has been connected to main earth mat.

CHECK FORMAT

7.8 Check Format



(Preferably with crane to unload the packages.

Yes/No


Challans GR etc.

Yes/No


carried out along with the erection contractor and preferably

with the manufacturer of the equipment.

Yes/No

4. In case of any damage the matter has been reported to the

manufacturer (or insurance agency if required)

Yes/No

5. Slack span stringing from dead end tower to the gantry has

been completed before taking up of the erection of line LA.

Yes/No

6. IR value of each stack has been measured Yes/No7. Insulators have been cleaned before erection at site Yes/No8. Mounting plate of structure top is regular and horizontall. Yes/No9. Level has been checked with a Spirit Level before mounting. Yes/No10. Terminal connectors have been tightened to proper torque. Yes/No11. When surge counter is not in use, base plate has been

positively connected to earth.

Yes/No

12. Surge Monitor has been earthed by connecting it to main earth

mat.

Yes/No

___________________________________________________________________

CHAPTER EIGHT

___________________________________________________________________

ISOLATORBack to contents page

8.0 Introduction


Isolators are disconnecting switches which are used for disconnecting

the circuit under no load conditions. They are installed in such a way

that a part of substation circuit can be isolated from other live parts for

the purpose of maintenance. Isolators play an important role in

maintenance of a substation. An isolator can be opened only after

opening the circuit-breaker. An isolator should be closed before

closing the circuit breaker. Opening and closing of a current carrying

circuit is performed by a circuit-breaker. An isolator does not have any

specified current breaking capacity or current making capacity. In some

cases isolators are used for breaking charging current of transmission

lines.

420 kV Centre Break Isolators are designed for independent single

pole operation or three pole electrically/mechanically ganged operation.

Single or Double Earth Switches, as required, can be fitted to them.

These isolators can be operated either manually or by motor. These

isolators are supplied in components and are assembled at site.

8.1 Construction features


CHAPTER-8ISOLATOR

420 KV Centre Break Isolator comprises of the following:

i) Support Structure

ii) Base Assembly

iii) Insulator Stack

iv) Male and Female contacts Assembly

v) Operating Mechanism (Main & Earth)

vi) Down Operating Pipe (Main & Earth)

vii) Tandem Pipe (Main & Earth)

viii) Earth Switch Assembly

8.1.1 Support Structure


i) Support Structure are made out of tube.

ii) They have the arrangement to fix over the foundation for fixing the

Base Assembly on the top of the structure and Operating

Mechanism Box (Main & Earth)

iii) Earthing strip fixing arrangement is also provided along with.

iv) These structures are designed to withstand all forces like short

circuit force, wind force and wind load etc.

v) Isolator structures are supplied in hot dip galvanised condition

8.1.2 Base Assembly


For every 3 pole switch there are 2 types of bases.

i) Base Assembly with drive arrangement and interlocking

arrangement (if the switch is with earth). Other base is without

drive arrangement

ii) Stoppers are provided in both ends to control the travel of Moving

Blades in both close and open position of isolator.

iii) Complete base assembly and other components are duly

galvanised

iv) Base assemblies are supplied with

a) Inter Post coupling pipe assembled and aligned condition

b) Inter-Lock arrangement in set condition

c) Levers are assembled with pins, friction washers, brass

washers and split pins.

8.1.3 Insulator Assembly


Insulators are selected to suit the basic insulation level, minimum

creepage and minimum bending load to suit the equipment design

requirement.

8.1.4 Male and Female Contacts Assembly


i) In male and female contacts assembly the current carrying parts

are made up of Aluminium tubes

ii) The male and female contacts (reverse loop design) are made of

Electrolytic Copper with Silver Plating.

iii) The Connecting Stem is made out of electrolytic copper with Tin

Plating/Aluminium.

iv) The current transfer part that connects the Aluminium housing and

stem is made out of Copper with Tin plating and assembled inside

the Housing.

8.2 Operating Mechanism


Two types of operating mechanisms are available in isolator.

8.2.1 Geared motor operating mechanism


This consists of a reduction gear assembly which is driven by spur

gear fitted with 3-phase induction motor through pinion gear,

necessary overload protection, control switches for local/remote

operation, limit switches and mechanical stoppers. The mechanism

can be operated manually in case of failure of supply.

8.2.2 Manual operating mechanism


i) Both the mechanisms are housed in a cabinet made of sheet steel.

Auxiliary switches having silver-plated contacts and positive wiping

action with adequate number of NO, NC and long wipe contacts are

provided.

ii) Front door of the mechanism box is provided with good quality

neoprene gaskets, which, on compression, when the door is closed,

ensures high degree of protection against polluted atmosphere. All

the boxes are metal treated before being taken up for painting.

Suitable terminal blocks made of highly non-inflammable

thermosetting plastic are provided for terminating control and

auxiliary wiring.

8.2.3 Earth Switch Assembly


i) The vertical lift earth employs a turn and thrust movement by

initially rotating through 90o and subsequently moving upwards by

approximately 100 mm.

ii) The earthing switches can be actuated on a individual pole basis or

3 poles can be coupled and actuated by a single drive.

iii) Moving Blade of earth switch is made out of aluminium tube and

contacts are made out of copper with silver plating.

iv) Mounting Base and all other parts are galvanised.

8.3 Receipt , Handling and Storage


i) All packages are to be carefully opened and verified for damages

and shortages, if any. These shortcomings have to be properly

intimated to the manufacturer as well as to the Insurance authorities

as the case may be.

ii) Handling of large crates should be handled by crane carefully.

iii) All items should be stored on ramps/platforms, free from water

logging.

iv) All items should be stored in upright position only.

v) Insulators are to be stored separately to avoid breakage’s.

8.4 Erection/Installations


8.4.1 Structures


i) Refer the site layout drawings and compare with equipment

General Assembly Drawing.

ii) Identify the structures according to the General Assembly Drawing

iii) Structure assembly is lifted and fixed over the plinth (Without

damaging the foundation bolts)

iv) Assemble washer, spring washer and nuts in all foundation bolts.

v) Check for level at the top of the structure in both directions by using

spirit levels. If required give shims below the base plate of structure

and tighten the nuts.

vi) All other structures should be assembled in similar way

8.4.2 Base Assembly


i) Identify the Base Assembly from Equipment General Assembly

drawing.

ii) Lift the base assembly by using proper ropes and place it over the

relevant structure

iii) After keeping it over the base without removing the rope align it to

the mounting hole of base and top plate of structure and fix the

bolts and nuts and remove the rope.

iv) Check for level of flanges in both direction by using spirit level.

v) If necessary add shims below the leg of the base and align it.

vi) Tighten all the Bolts.

vii) Repeat the installation process for other two poles also.

viii)Ensure the Centre line of same pole and centre line of other

phases are aligned

ix) After completing the installation keep all the base assemblies in

open position

8.4.3 Insulators


i) The top middle and bottom units of Insulators should be identified

by using Insulator Drawing.

ii) The bottom and middle units are assembled together by using

proper bolts and nuts. Lift the Insulator stack by using proper

hook and placed over the base assembly by ensuring the top 4

holes position.

iii) Without removing the hook align the holes and fix all bolts.

iv) The level of top surface of insulator should be checked by spirit

level/plumb and if necessary the shims should be inserted below

the bottom flange of the insulator or/and between two insulator unit

flanges .

v) Now rotate the shaft assembly & check for the rotation of insulator

& its eccentricity.

vi) The same procedure is to be repeated for the other side of same

pole also

vii) In the same way the top unit of insulator and middle unit are

installed On both sides.

8.4.4 Contacts Assembly (Male and Female Assembly)


i) Identify the Assembly as per General Assembly Drawing

ii) Keep the Insulator corona ring on top of the Insulator

iii) Lift the Male Assembly by using proper sized rope and place it

over the insulator above corona ring.

iv) Without removing the rope align the holes and fix the screws.

v) Repeat the similar process for female assembly.

vi) Rotate the bearing shaft assembly and check for alignment of

Contacts assembly for horizontal alignment. Shims should be

inserted between the mounting flange of Assembly and top of

the insulator at relevant side. Similarly for vertical alignment

necessary shims should be inserted between insulator flange and

top of shaft assembly flange.

vii) If the entry is not smooth, loosen the contacts Mounting screws

and push the contacts forward or backward to get free entry.

viii) After achieving the entry check for centre line of Male and Female

in both directions.

ix) Now moving part should be rotated 2 to 3 times to ensure the

proper alignment

x) The Corona ring assembly should be identified for male and

female unit and connected properly to it.

xi) Moving part should be operated two to three times for checking

the free movement and also check that the contact corona ring

are not fouling each other

8.4.5 Connecting Disconnector


i) Manually set mechanism and disconnector to be connected into

fully OPEN position (Arrow mark on top of mechanism cabinet

indicates the 'open' and 'close' positions).

ii) If mechanical interlock keys are fitted, it will be necessary to

obtain the relevant keys to make mechanism operational.

iii) Align the fixing hole and bolt them together to achieve desired

tightness.

iv) Ensure that the mounting channel on the drive and the structure

are matching.

v) Level the box by placing the spirit level on output shaft flange in

two directions.

vi) Provide shim wherever required.

vii) Check for centre line and verticality between torque bearing

flange and drive flange with a plumb.

viii) Introduce Universal Coupling as called for in the General

Arrangement Drawing.

ix) Measure exact height between torque bearing flange and top of

universal flange.

x) Cut the operating pipe with the specified clearance to facilitate

smooth entry.

xi) Weld the vernier flange properly keeping the flange

perpendicular to the centreline of the pipe. Level and bolt the

same. The drive is now ready for operation. Mounting angles of

mechanism to structure are slotted to provide horizontal

adjustment. Adjust the mechanism so that the vertical drive

tube rotates TRUE.

xii) Cabling (internal/external) be completed as per schematic

drawing. Ensure that all electrical interlocks are wired properly.

xiii) Before energising the circuitry, interlock wiring and control wiring

should be checked by multimeter (as per schematic drawings)

8.4.6 Controls for Electrical Operating Equipment


A hinged panel on the right hand side of the cabinet carries the

electrical controls for operation of the mechanism. Controls for normal

operation are mounted on the front of the panel and are accessible

immediately the outer cabinet door is opened

These comprise :

i) Local OPEN and CLOSE Control Switch

ii) In case of individual pole drives the master control cabinet will

have push buttons for operating/closing also.

iii) Local/Remote Selector Switch

iv) Heater/Light Switch

8.5 Closing Operation of Isolator


i) Ensure all castle keys are in position.

ii) Once the associated circuit breaker is open, closing contact will

energise the interlock thereby making availability of supply at the

local/remote selector switch.

iii) Set the electrical remote selector to local position as required and

then press push button for closing, thereby causing the closing

contactor to pick up.

iv) The hold on contact of closing contactor will now be closed there-

by retaining the supply after the push button is released.

v) Simultaneously contacts of closing contactor will close, thereby

supply to motor is made available.

vi) Ensure motor direction is towards closing. Otherwise alter the

phase sequence at motor terminal box.

vii) The isolator will start to close, and at the end of the closing

operation, limit switch for closing will open then de-energising the

closing contactor.

viii) The circuit is now de-energised and the closing operation is

completed.

ix) Car should be taken to prevent the mal-functioning. Contact

closing (CC) of the closing contactor will isolate the opening

circuit, once closing contactor is energised.

8.6 Tandem Pipe Assembly


i) After single pole trial with motor keep that pole in closed

condition

ii) Fix other two poles also in closed condition (set the stopper

screws)

iii) Measure the distance between the lever of two adjacent poles

('R' & 'Y')

iv) Check and set the Tandem, pipe length on the floor itself

v) Lift the Tandem pipe by using proper rope and fix one side first

by using suitable anti friction washers, brass washers and split

pins.

vi) Fix other side in the same manner.

vii) Operate the operating mechanism and check for proper closing

and opening of both poles. If required do minor adjustments in

Tandem Pipe by length by using adjusting screw. Then finally

lock the adjusting screws by check nut.

viii) Repeat this process for the other poles ('Y' & 'B')

8.7 Earth Switch Assembly


i) Identify the Assembly to fix the fixed contact assembly through

General Arrangement Drawing

ii) Take the Earth fixed contact assembly and fix it with the Hamper

Assembly by using proper sized Bolts as per General Assembly

Drawings. The above assembly can be carried out before

installing the Hamper Assembly over the insulator.

iii) Lift the Earth Blade Assembly by using rope and fix it with base

assembly using the middle set of mounting holes to hold the

assembly in place.

iv) Attach counter balance weights in pendulum arm at suitable hole

and check the position of Earth Switch which should be parallel to

ground.

v) Manually move earthing blade towards closing position .To adjust

add shims at the back of the mounting plate to tilt the earthing

blade in required direction.

vi) Continue to move earthing blade towards closing and observe

that the contact fingers come into the fixed contact. A small

adjustment to twist the contact fingers is possible by shimming

mounting plate.

vii) Continue to close earthing switch until contacts are fully engaged

i.e. when the insulated stop of the earthing blade comes to rest

without straining against fixed contact.

viii) Tighten all fixing bolts and keep the earth switch in closed

position.

DO’S DON’TS&

SPECIAL PRECAUTIONS



i) Before the isolator is put into operation, the motor is to be

meggered and the contacts are cleaned.

ii) The mechanism box always is to be kept free from moisture.

Hence, space heaters are provided in the mechanism box.

iii) Also rubber beading should be kept in good condition.

iv) Cable glands should be properly fitted at the entry of the cables

and extra holes are plugged properly to avoid hazards.

v) For transportation, individual base and bearing pole assemblies &

the male and female contact arms should be packed separately.

The Insulators and drive boxes should also be packed separately.

vi) The bolts and nuts required for mounting the base to the structure

and the Insulators to the base are packed separately as loose

items, while all the other hardware (bolts & nuts) are fitted in their

respective places. Care should be taken that these are removed

only at the time of mounting to respective assemblies.

vii) All the assembles should be stored well preferably in a covered

area to avoid any damage/pilferage during storage.

8.8.1 Adjustment in drive/assembly erection


i) Manual

a) By use of emergency handle, operate the coupled disconnector

and observe whether it is fully OPEN or CLOSE at each end of

its operating cycle

b) If isolator does not CLOSE fully remove clamping bolts and turn

mechanism slightly towards /OPEN and retighten bolts proceed

turning isolator towards CLOSED.

c) Repeat until satisfactory operation is obtained.

ii) Electrical

a) Make electrical connections by referring to contract diagram of

connections of incoming supply.

b) Do not attempt to operate the disconnector under power at this

stage.

c) When selector switch is fitted set it to LOCAL

d) When AC Motor is fitted manually set mechanism to mid position.

e) Operate control Switch and at the same time observe whether the

mechanism rotates towards the selected position

f) If it rotates in opposite direction to that selected stop motor

immediately by switching off power supply.

g) If necessary reverse the to phases of motor supply.

iii) Open and Close Push Buttons

The Control Push Buttons determine the direction of travel of the

isolator. When a cycle is initiated by switching to the appropriate

position the isolator will open or close. Once the mechanism has

received a signal the push button can be released. The

mechanism will complete the operation and will not respond to

further signals until it has completed its operation. An indicator,

shows the isolator position either OPEN or CLOSE outside the

cabinet at the base of the output shaft.

iv) Selector Switch

When the selector switch is set to LOCAL, operation of the

mechanism will be governed by the controls in the cabinet.

Setting the selector switch to REMOTE transfers controls of the

mechanism to remote control point.

v) Heater and Heater Switch

An anti-condensation heater is fitted in the bottom of the cabinet.

It should be switched on at all times, ensuring that the

temperature inside the cabinet exceeds the temperature

outside. The heated air leaves the cabinet by way of breather

around the output shaft and cool air is sucked in. A switch is

mounted on the front of the control panel for the control of the

heater through a thermostat.

vi) Open and Close Contactors

These contactors are mounted side by side on the rear of the

electrical control panel. They directly control the reversing

operation of the motor. Further contacts are used for electrically

interlocking the contactors, providing a sealing circuit across the

'OPEN' and 'CLOSE' Push Buttons.

vii) Auxiliary Switches

Silver plated contacts with a positive wiping action are used

giving reliable making of low current signalling circuits under

adverse climatic conditions.

viii) Fuse Links

Fuses for the control and heater circuits are mounted on the

control panel. Connections to these are made in the same

manner as connections to terminal blocks. The fuse wire is

routed through the top of the carrier. The current ratings of fuse-

links are shown on the schematic diagram drawing.

For opening the Isolator a similar sequence of operation will be

executed by pressing the push button for opening.

ix) Manual Operation

The mechanism may be operated manually in the event of a

motor power failure with the help of manual operating handle.

CHECK FORMAT

8.9 Check Format



(Preferably with crane) to unload the packages.

Yes/No


Challans GR etc.

Yes/No



with the manufacturer of the equipment.

Yes/No

4. Any type of damage to the equipments/components during

transportation or any missing items has been brought to the

notice of the panel supplier.

Yes/No

5. Site where isolator is to be erected is ready before the starting

of erection work.

Yes/No

6. Level of the structure assembly has been checked during

erection using spirit level

Yes/No

7. Site where isolator is to be erected is ready before the starting

of erection work.

Yes/No

8. Level of the top surface of isolators has been checked during

erection, alignment & level of equipment

Yes/No

9. Centre line of all the poles in different phases are aligned. Yes/No10. Centre line alignment of male & female assembly has been

checked

Yes/No

11. Before fitting, the crane rings have been identified for male and

female assembly

Yes/No

12. Moving parts have been operated 2-3 times for checking the

free movement

Yes/No

13. The rotation of motor is in right direction Yes/No14. In case it is in opposite direction the same has been corrected

by altering of the phase sequence of the motor terminal.

Yes/No

15. Lifting of tandem pipe assembly is with proper size rope Yes/No16. During erection movement of earthing blade has been checked Yes/No17. Contact fingers of earthing blade and moving towards the fixed

contact

Yes/No

18. All fixing bolts have been tightened to keep the earth switch in

proper close/open position

Yes/No

CHAPTER-9CURRENT TRANSFORMER

___________________________________________________________________________

CHAPTER NINE

___________________________________________________________________________

CURRENT TRANSFORMERBack to contents page

9.0 Introduction


Current transformers are used for reducing/stepping down ac current

from higher value to lower value for measuring /protection /control. CTs

have low VA rating.

Rated characteristics of CTs used for High Voltage metering/ protection

are given below:

i) Rated primary current

ii) Rated short time current (primary)

iii) Rated secondary current

iv) Rating exciting current

v) Rated burden

vi) Current error or ratio error

vii) Phase angle error

viii)Composite error

ix) Accuracy class

i)Over current factor

ii)Insulation level (primary)

9.1 Construction Features


Construction-wise the Current Transformer may be of following two

types:

Hair Pin design or dead tank type and Top dome design or Dead Tank

design. In the hairpin design the primary conductor enters from the top

of insulators and passed through the tank. The secondary core is

wound on the primary inside the tank. The body of tank is earthed to

the switchyard earthing. Current Transformers of WSI, BHEL, ABB are

of this type. In the other top dome design the Primary conductor goes

straight in the dome shaped tank at the top. Secondary winding is

wound against it. As the tank body is always live this design is known

as the live tank design. Current Transformers of CGL, RK are of this

design. As the head is heavy, more care is required while lifting and

alignment of the CT.

The Current Transformer essentially consists of primary and secondary

coils and core. The core is constructed in the form of rings. The

secondary winding is wound uniformly over the insulated ring cores.

The secondary terminals are brought out through a terminal board into

the terminal box. From terminal board the connections are given to the

terminal blocks. The control cables are connected to the terminal

blocks.

The primary winding consists of Copper strips/Aluminium pipe (with

single turn) over which high quality insulation paper is wound.

Aluminium foil is wrapped at suitable intervals over the insulation paper

to get a constant voltage gradient along the arcing distance of the

porcelain insulator. The insulated primary passes through the

porcelain insulator and taken out through 4 nos. terminal bushings

(each rated for 1200 A) fixed to the wall of the expansion chamber.

The respective terminal bushings are shorted internally. The primary

conductor has sufficient cross sectional area to meet the continuous

and specified short-time current ratings.

The outer surfaces of ferrous parts are given light grey enamel paint to

shade over rust inhibitive coat of ready mixed zinc chrome primer.

Steel surfaces coming in contact with transformer oil are given a coat

of oil resisting varnish. Galvanised bolts and nuts are used as

fasteners. All welded and gasket joints are subjected to leak tests.

9.1 Hermetic Sealing


The current transformer is subjected to heat and vacuum cycle in a

drying chamber to extract the moisture from the insulation paper. After

drying and oil impregnation under vacuum, the current transformer is

hermetically sealed with dry Nitrogen gas above oil. When the oil

expands or contracts due to temperature variations, the Nitrogen gas in

the chamber undergoes change in pressure. Depending on the

pressure and temperature, a part of Nitrogen gas in the chamber

undergoes change in pressure and a part of Nitrogen gas will be

absorbed by oil. The volume of expansion chamber and the gas

pressure at the time of initial filling are adjusted so that the gas

pressure will be less than + 0.5g/cm2 at 75oC and above -0.2 kg/cm2

at 0oC. A drain valve is provided at the bottom of lower tank. Some

CTs come with rubber/teflon/steel bellows to take care of temperature

variations. Such CTs are not filled with Nitrogen gas.

9.2 Transportation, Unpacking & Inspection


i) The 400 kV current transformer is dispatched in the horizontal

position (with the oil level gauge side at the top) fixed to a

transportation frame in wooden crates whereas 220 kV CT is

positioned vertically in packing.

ii) Special oil sealing arrangement is provided in the expansion

chamber to prevent contact of Nitrogen gas with paper insulation

when the current transformer is in the horizontal position.

iii) For unloading /loading the crates, crane should be used in store

and switchyard. However, truck should be used for transporting

the CT from store to switchyard.

iv) CT at site should always be lifted from lifting brackets which are

provided on the base.

v) Unpacking of wooden crates should be done with particular care

so as not to damage the porcelain insulator and terminal

bushings.

vi) After receiving at site CT should be checked for any physical

defect.

vii) The name plate readings/rating of CT should confirm to

technical specification of our LOA.

viii) All the crates containing different parts of CT should be checked

with the store challans/MICC/Packing list etc.

ix) CT should be lifted by crane using chains/strings from the

indicated handling points on crates.

x) 400 kV CT is to be made vertical immediately on receipt at site

and kept in vertical position only.

9.4 Installation/Erection


i) As the current transformer is dispatched in completely assembled

state, it can be installed directly after making it upright. It is to be

ensured that before commissioning, the porcelain insulator is clean

and free from all dust, grease and particles of packing material.

ii) Alignment of the support structure should be checked with

spirit/water level.

iii) Place the CT on duly levelled supporting structure by using a crane.

iv) Care should be taken such that primary polarity of erected CT is

correct and as per relevant drawing.

v) Fix the CT with four anchor bolts to the supporting structure.

vi) Now the crane can be removed after tightening the bolts & nuts.

vii) Provide proper earthing of transformer from the base of CT.

Earthing connection should be permanent.

viii) Lay the control cables from control room relay panels and

connect to CT marshalling box.

ix) Control cables should be laid in trays or in pipes.

x) Marshalling box of CT should also be earthed.

xi) Cabling work on secondary side should also be completed & its

IR valve be ascertained.

xii) Cable continuity should be checked after erection is completed.

xiii) Star point should be earthed properly.

xiv) Care should be taken during handling, lifting, loading or

unloading and erection no damage is done to CT insulator by

slings. Proper cushioning arrangement should be used for the

same.

xv) The receipt storage and erection should be done as per the

approved FQP.

xvi) The threaded fasteners should be clean & tight and missing or

broken fasteners should be replaced.

xvii) It should be ensured that all the times the oil in CT is at the

specified level and there is no leakage of oil.

xviii) The primary injection test of CT should be carried out as per the

prescribed procedure.

xix) Any secondary core of CT that is not being put in service should

be short circuited.

xx) Polarity of all secondary cores should be checked.

DO’S DON’TS&

SPECIAL PRECAUTIONS

9.5 Do’s Don’ts & Special Precautions


i) In order to keep the unit hermetically sealed, the flanged joints with

gaskets in between should not be tampered with. The cover of the

secondary terminal box alone needs be opened for giving

connections to control cables.

ii) Since the current transformer is hermetically sealed and uses no

material harmful to oil, there is no necessity for extraction of

samples of oil for analysis or for reconditioning of oil. Check for

Nitrogen gas pressure is also not required. If oil level is below the

red mark it indicates leak and should be investigated.

iii) In case of heavy pollution deposits due to surrounding atmospheric

conditions, periodic external cleaning of porcelain insulator and

cleaning/painting of other exposed surfaces can be carried out (as

per the specific instruction of the manufacturer)

iv) Precautions should be taken not to keep open secondary circuit

when current is flowing in the primary as this may cause

overheating of core and breakdown of the insulation due to high

voltage developed across the secondary terminals.

v) The lower tank should be earthed in a positive and permanent

manner before commissioning.

vi) The CTs are dispatched with secondary terminals short circuited.

Care should be taken so that the shot circuiting links at the

terminals are not disturbed.

vii) For lifting the CTs at site one should look for proper handling points

for using slings and read the specific manufacturer’s instruction to

avoid any mishap.

viii)Weight of the CT should be read from the name

plates/specifications & lifting tackles of ample capacity should be

used.

ix) Crates of CT should be lifted without jerks or vibrations and placed

at the desired place without dropping or hard hitting on ground.

CHECK FORMAT

9.6 Check Format



(Preferably with crane) to unload the packages.

Yes/No


Challans, GR etc.

Yes/No



with the manufacturer of the panels.

Yes/No

4. Any type of damage to the packing during transportation or

any missing items has been brought to the notice of the

manufacturer.

Yes/No

5. The unpacking of CT has been done carefully to avoid any

damage to it.

Yes/No

6. Site where CT is to be erected is ready before the starting of

erection work.

Yes/No

7. It has been checked that there is no leakage of oil from CT Yes/No8. Cranes or other good quality lifting T&P is available at site to

transport/ CT from store to site and for erection

Yes/No

9. Care has been taken to avoid any damage to insulators

during lifting (by providing cushion of suitable material)

Yes/No

10. Oil level in CT has been checked Yes/No11. IR value of primary and secondary winding recorded &

satisfactory results are obtained

Yes/No

12. CT has been placed on the support structure very carefully

and all nuts have been tightened.

Yes/No

13. The structure/equipment has been levelled Yes/No14. The polarity of CT is correct Yes/No15. The table of CT has been earthed at two points Yes/No16. The marshalling has been checked for heating and lighting

arrangement

Yes/No

17. The cable work between C&R panel to marshalling box is

complete.

Yes/No

18. Continuity of all cables has been ascertained Yes/No19. Primary injection test of CT at relay terminal has been

performed as per prescribed procedure.

Yes/No

20. Secondary core of CT that is not in use has been short

circuited.

Yes/No

CHAPTER-10CAPACITIVE VOLTAGE TRANSFORMER

___________________________________________________________________________

CHAPTER TEN

___________________________________________________________________________

CAPACITIVE VOLTAGE TRANSFORMERBack to contents page

10.0 Introduction


Capacitive voltage transformer can be effectively employed as a

potential source for metering, protection, carrier communication and

other vital functions of an electrical network.

In the case of EHV systems CVTs are always supplied in multi-unit

construction. The multi-unit construction enables ease of transportation

and storage, convenience in handling and erection etc.

10.1 Description & operating principle:


The Capacitive Voltage Transformer comprises of a Capacitor Divider

along with its associated Electro-Magnetic Unit. The Divider provides

an accurate proportioned voltage, while the Electro-Magnetic Unit

transforms this voltage, both in magnitude and phase to convenient

levels suitable for metering and protection.

The Electro-Magnetic Unit (EMU) comprises of the following

components;

Compensating Reactor

Intermediate transformer

Damping device

The compensating reactor is used for tuning CVTs to the desired rate

frequency of 50 Hz. Since the CVT comprises of capacitors the compensating

reactor plays the role of nullifying the capacitive effect of reactance due to the

capacitance of the CVT.

The capacitor unit comprises of HV capacitor C1 & intermediate

voltage capacitor (C2). These capacitor consist of oil impregnated,

series connected capacitor elements; housed inside oil filled porcelain

insulators. Each capacitor unit is hermetically sealed.

i) Capacitor Units

It comprises of metallic bellows to compensate for volumetric

expansion of oil inside the Porcelain. In case of multi-unit stack all the

potential points are electrically connected and shields are provided to

overcome the effect of corona and RIV.

ii) Transformer

The voltage tapped from the intermediate point of the capacitor is fed

to the primary of the transformer through the choke. This tapped

voltage is stepped down by the intermediate voltage transformer to the

required rated secondary voltage.

Typical Transformer Ratings

In case of 400 kV/4000/6600 pf and 400 kV/8800 pf CVT the rating

of transformer may be

Table -1: Rating of Transformer

1. Rated primary voltage 22/3 or 20/3 kV rms (Primary of

intermediate voltage transformer)

2. Rated secondary voltage 110/3 V (across each secondary

winding)3. Total simultaneous burden 300 VA for 0.5 class accuracy4. Rated output burden and accuracy

class per winding

Winding 1 : 200 VA 3P

Winding 2 : 200 VA 3P

Winding 3 : 100 VA 0.5

The transformer is made up of CRGO laminations of core type design

over which primary and secondary windings are wound around the

laminations. The insulation between the core and the windings and

interturn insulation is done by means of paper.

iii) Details of capacitor divider unit :

The Capacitor divider unit is used acts as a

i) Coupling capacitor for carrier communication.

ii) Voltage divider for stepping down the voltage to a suitable

level.

This stepped down voltage is fed to the primary of the

transformer through a choke (compensating reactor) which is

housed inside the electromagnetic unit.

The Capacitive Divider normally comprises of capacitor

elements of cellulose paper dielectric with aluminium foil

electrode. These elements are identical and are connected in

series by using copper taps. Hence the voltage across each

element is identical. The reduction in voltage is achieved by

taking tap from one of the capacitor elements.

10.1 Packing and Transportation :


i) All Capacitor Units or the Capacitive Voltage Transformer are

securely packed in wooden crates. The Electro-Magnetic Unit

forms an integral part with the capacitor unit. In the case of Multi-

Unit type, the bottom most capacitor unit is hermetically associated

with the Electro-Magnetic Unit. Each wooden crate is identified with

the corresponding serial number of the unit inside.

ii) Each Capacitor unit has one Name Plate designating the rating of

the unit. Position of the Unit in the complete assembly is also

indicated in the Unit Name Plate by incorporating Top Unit or

Middle Unit or Bottom Unit.

iii) Bottom-most unit of Multi-Unit stack has one Master Name Plate

fixed on to the Electro-Magnetic Unit and one unit Name plate fixed

on to the bottom flange.

iv) The transportation must be performed in vertical position only.

Transportation should be carried out as smoothly as possible

without undue jerks.

v) The unpacked parts of the device should also be moved in the

same vertical position as within the packing

10.3 Receiving


While receiving the CVT the site should check :

i) That the right CVT has reached at the destination with regard to its

voltage and other rating particulars.

ii) Ensure that CVTs are not mislinked.

iii) Look for transit damage before proceeding with any unloading

operation. Where a doubt arises, apprise the insurance authority or

insist on open delivery from the Transport Carriers.

iv) Inspect for breakage’s. In case of the manufacturer should be

notified immediately.

v) During handling, ensure that the capacitor Unit is always its upright

vertical state.

10.4 Unloading :


Before unloading the crate(s) of the CVT from the carrier or

transporting vehicle

i) Carefully observe the instructions on the wooden crates.

ii) It is important to look for sling or chain markings, supporting points

etc. and use them.

iii) Ensure that the Top and Bottom ends of the crates are in order.

iv) Make arrangements for unloading with derricks or cranes and with

associated hoisting facilities.

v) Unload the crates one by one, taking all precautions required for

fragile material.

vi) As all porcelains are fragile and are susceptible to breakage, avoid

knocks and jerks during handling.

vii) The base unit should be lifted with crane by means of lifting lugs

provided on the EMU cover. Otherwise there is danger of breaking

a porcelain bushing.

viii)For taking the capacitor unit out of packing, use lifting lugs provided

on top cover of capacitor.

ix) While unloading/unpacking, vibrations, shocks are to be avoided.

x) The separate capacitor unit must be short circuited by bare wire

between head & bottom flange until erection and connection are

completed.

10.5 Storage


i) CVTs are dispatched with the terminals short circuited. Store

the Capacitor Voltage Transformers taking care that the short

circuiting at the terminals is not disturbed.

(ii) A free capacitive voltage transformer with its terminals not short

circuited picks up dangerous potentials which may cause

injuries to personnel.

iii) It is also to be ensured that the CVT should be kept always in

vertical position.

iv) When not in use keep the Capacitive Voltage Transformers away

from energised locations, water logged areas, marshy or humid

locations.

v) When CVT is to be stored, it should be put back into trapezoidal

crate/packing case.

If prior to the installation, the CVT is to be stored for longer

duration without usage, the following tests may be carried out

on the CVT.

a) Visual inspection as per approved drawing

b) Measurement of capacitance

10.6 Installation


i) Before proceeding with the installation, keep all the units near

the erection site.

ii) Ensure that the Top, Middle and Bottom units are (if applicable)

properly identified as per their serial numbers indicated on the

name plates.

iii) Base unit is to be fixed on a supporting structure with bolts of

specified size.

iv) For fixing the base unit, 4 holes are provided on the bottom plate

of the EMU unit.

v) If, there is an upper capacitor unit then it is to be fixed with the

top flange of the lower unit with the help of studs, nuts and

washers

vi) For assembly of capacitor units which have antifog shads on the

porcelain or which have broaden sheds, the threaded studs

used for coupling have to be first held into the through holes of

the flanges, before the units are placed are above the other.

The assembly has to be done with utmost care, to prevent

damage to the porcelain sheds.

vii) For handling the base unit & upper capacitor during the erection

process, use of crane is necessary.

viii) The studs used for coupling the capacitor units have to be

tightened with the specified torque.

10.7 Connection


i) The upper terminal of individual capacitor unit should be short

circuited to the base by basewire till all connections are

completed and unit is ready for commissioning care should be

taken to remove this bare wire prior to commissioning.

ii) The tank of CVT base of CC should be earthed properly at two

independent places

iii) In case of CVT if carrier frequency terminal is not to be used it

should be earthed on the steel tank.

iv) The line matching unit is to be connected between HF bushing

outdoor and earth if CVT is used for carrier coupling otherwise this

terminal is to be earthed.

v) Connection work in the secondary terminal box should be done

when HV terminal is earthed.

vi) The cables with large cross sections are inserted through the

bottom of the terminal box. The connections should correspond to

the circuit diagram on the inner side of terminal box.

vii) The earthing of secondary winding (s) must be done either in the

terminal box at the beginning or at the end of cable but not at the

both ends. It is preferable to earth the secondary terminal in

terminal box.

viii)However for open-delta connection protection scheme for earthing

of secondary winding should be referred.

ix) The quick acting fuses for each secondary windings are mounted in

the terminal box itself.

x) The secondary terminals must not be touched and the head of the

person attending this job should be below the level of the tank

cover.

xi) Only metering winding for monitoring equipment and protecting

winding for protective equipment should be selected.

xii) Unused secondary windings should be left open circuited and in no

case they should be shorted.

xiii)The tank should be earthed by means of copper conductor, the

cross section of which complies with the statutory regulations. One

end of the secondary winding should also be earthed.

xiv)After confirming the low voltage ratio, connect the HV terminal to

the line by terminal connector. While clamping the terminal

connector proper torque should be applied to ensure firm

connection.

xv) It should be ensured that the jumper is rightly connected to the

primary terminal of CVT.

xvi)Pre -Commissioning checks should be carried out as per the norms

of Corporate Operation Services Department.

DO’S DON’TS&

SPECIAL PRECAUTIONS



i) In case of multiunit construction the capacitance of each divider is

to be measured separately. In case of bottom divider the same has

to be removed along with the bottom flange from the EMU tank.

ii) After removing the bottom divider from the EMU check for any loose

connection of EMU. This test may be carried out using the shearing

bridge.

iii) Measure the depth of the bellow.

iv) In case of any evidence of traces of oil do not energise the CVT.

v) Measurement of voltage ratio

vi) Apply a very low voltage say 230 V and measure the secondary

voltage across each winding. It should be matching the

specifications of the manufacturer.

vii) Carry out the meggering test on LV terminal of EMU by using 500 V

megger.

viii)The measured value should not be below 10 M ohms.

ix) Check the resistance of the damping resistors after disconnecting

the connecting leads from the secondary terminal studs.

x) The CVT should always remain in its upright position to safeguard

mechanical arrangement of the internal active parts.

10.8.1 Inspection before mounting


i) Oil level in the tank is to be checked. The red line on the oil level

gauge indicates rated oil level at 20o C.

ii) Tightness of the tank and capacitor units is to be checked. All units

(oil level gauge, cover, oil drainage joints) should be checked for oil

levels.

iii) A leakage at the insulator indicates defect in transportation. In case

any leakage is detected, the unit should not be installed and

manufacturer to be contacted.

iv) Before the CVT is placed in position, check with a 500 V DC

Megger whether the internal connection to the primary and

secondary windings are intact and property connected.

v) CVT secondary winding should never be short circuited.

vi) While connecting the measuring instruments, protective relays to

the secondary terminal, ensure the load/burden on respective

secondary winding is not exceeded.

10.8.2 Defect/Damage


i) If defect/damage is noticed, matter should be reported without any

delay to the manufacturer with full details like type, designation

and serial number of equipment, nature of defect/damage and exact

location of defect .

ii) When the device i.e CVT/CC consists of two or more than two units

it must be insisted that each upper unit is mounted up on

corresponding base unit.

iii) The units are calibrated at manufacturer’s works before they are

despatched. Therefore pay attention to date (manufacturing no,

from the last certificate) on the rating plate and on special plate at

top cover of the upper units. Upper units pertaining to different CVT

should not be assembled together.

iv) Corona shield in two halves are supplied loose in the same packing

case and it is to be fixed after mounting top units. In case of multi

unit CVT the unit with single capacitor stack is generally supplied

with Corona shields duly mounted.

v) Small repairs (defects on surfaces) may be done at site. Leakage

should be reported to the manufacturer with a statement of Item

No., Order No., date of commissioning and other specifications.

10.8.3 Minor Irregularities


i) Should the insulator gaskets begin to leak slightly for instance,

tighten up the clamp holding the insulator in an attempt to stop the

leakage. The nuts should be tightened up successively by about

1/6 of a turn until they are all uniformly tight the maximum torque

being 70 kg-cm.

ii) Careless excessive or uneven tightening of the nuts may damage

the insulator If tightening up does not stop the leakage the matter

should be reported to the manufacturer.

iii) If a secondary bushing, is leaking try to stop the leakage by

tightening the nuts slightly. If the leakage does not stop, matter

should be reported to manufacturer.

10.8.4 Erection


During installation the studs used for coupling capacitor should be

tightened by applying torque of specified strength.

i) During erection process of CVT at site preferably the crane should

be used for handling the different units.

iii) It is to be ensured that capacitor unit with same serial numbers

are coupled during erection of CVT with 2 or more capacitor

units.

iv) Upper as well as the lower capacitor unit has to be short

circuited & connected to earth, until the erection and

commissioning work is being done on the CVT. (The capacitor

get charged by the electrical fields in the vicinity and they keep

these changes for a long time, which can be dangerous to

human life. Hence the shorting of capacitor unit is necessary).

v) No screwed joint of the capacitor units and base units should be

unscrewed.

CHECK FORMAT

10.9 Check Format


1. Different CVT units have been transported and stored in

vertical position

Yes/No

2. Physical verification of CVT done as per specifications,

challans, BOQ, MICC etc.

Yes/No

3. Unloading of CVT done using crane Yes/No4. CVT checked for any physical damage, discrepancy etc. Yes/No5. Oil level in CVT is OK Yes/No6. In case of any damage/discrepancy same has been reported to

supplier/insurance agency.

Yes/No

7. Proper lifting arrangement for different CVT items at site being

provided

Yes/No

8. Mounting bolts of base plate have been tightened properly Yes/No9. Various parts of CVT joined and tightened to the designed

torque

Yes/No

10. HF terminal of unutilised CVT is properly earthed Yes/No11. Care has been taken to avoid short circuiting of CVT

secondary winding

Yes/No

12. Crane is used for handling the capacitor units Yes/No13.Different erection activities performed as per approved FQP. Yes/No14. Fuses in CVT marshalling box are OK Yes/No15. Cable laying activity is complete from relays to marshalling box Yes/No16. Proper earthing of CVT tank has been done Yes/No17. Terminals have been properly tightened. Yes/No

CHAPTER-11POWER LINE CARRIER

COMMUNICATION

___________________________________________________________________________

CHAPTER ELEVEN

___________________________________________________________________________

POWER LINE CARRIER COMMUNICATIONBack to contents page

11.0 Introduction


In the modern Power System network for stable operation of large

network a reliable communication is required. Difficulties in obtaining

reliable and cost effective communication medium limit the choice of

the Communication medium to power line carrier (PLC). The same

power lines carrying the Electrical Energy are utilised for

Communication.

11.1 PLC System


PLC system are principally used to carry information in the form of

speech or the form of data representing Telemetering, Telecontrol,

Teleindicator and Teleprotection. The signals are transmitted by means

of H.F. carrier Trans/Receiver, the carrier frequency may be anywhere

between 30 kHZ and 500 kHZ the information wave band is 300 HZ

to 3.4 kHZ.

Speech Band = 300 HZ to 2 kHZ

Data Band = 2 kHZ to 3.4 Khz

11.2 Coupling Equipment


To enable the Power Lines to be employed for Communication

purposes some from of coupling equipment is required which will

permit the injection of Higher frequency carrier signals without undue

loss and at the same time de- couple the Communication equipment

from the power unit.

11.3 Coupling Equipment Description


Essentially Coupling Equipment Comprises of the following

i) Capacitive Voltage Transformer (CVT)

Coupling capacitor (8800 pF to 22000 pF) of suitable voltage

withstanding capability is inserted between the carrier

equipment and HV Line which isolates the H.F. equipment

connected on LV side from HV side. The coupling capacitor

passes the H.F. frequency signals and blocks the power

frequency signals towards carrier section.

ii) Wave Trap/Line Trap

The coil is rated to carry full line power frequency current; the

rating of choke is 0.1 to 1.0 mili Henry. Tuning pot in parallel

with coil is used as tuning device to block the carrier frequency

entering the substation. Line trap unit is inserted between

busbar and connection of coupling capacitor to the line. It is

parallel tuned circuit comprising L and C. It has a low impedance

(less than 0.1 ohm) to 50 Hz and high impedance to carrier

frequencies. This unit prevents the flow of carrier signal towards

substation and at the same time offers negligible impedance to

the power frequency current.

The line traps are connected in series with the high voltage lines

on the station side. These are designed for the following ratings:

Normal power frequency current

Short-time short-circuit current

Basic insulation level characterised by the normal power

frequency voltage, lightning impulse withstand voltage and

switching impulse withstand voltage.

11.4 Constructional Features


The line trap unit comprises of the following main parts:

Main coil

Tuning Unit

Lightning Arrester.

Corona ring for 400 kV Line Trap (this is generally supplied loose, it

should be fitted before lifting for erection)

11.5 Data Transmission


The important analogue and digital parameters of the substation are

transmitted to the load despatch centres for SCADA and EMS

functions.

11.6 Teleprotection


For high speed protection particularly at 400 kV system the fault should

be isolated within 100 ms time. Use of carrier signals help in reducing

the fault isolation time.

11.7 Carrier Panel


In the transmitter section, the AF signal is converted into H.F. signal in

two stages, i.e. first AF is converted into IF (Intermediate frequency )

and then converted into H.F. (higher frequency). Apart from the

signals i.e. (speech, data and Teleoperation) the other signals which

are internally generated i.e. pilot and auxiliary are also converted into

H.F. stage. The pilot is normally used for calling opposite station either

through dialling or through express. It also does the main function of

guarding the receiver against generating AGC voltage (automatic gain

control). The purpose of Aux. Carrier is to see that transmitter and

receiver work in frequency locked mode.

11.8 Earthing


The last but not the least important is earthing of the PLC terminals and

panels. The earthing should be proper and common with Substation

earthing to safeguard the Electronic Component and working personnel

from any voltage gradient. Earthing at different points may lead to

excessive currents between outdoor and indoor PLCC equipment.

These excessive current can damage the output stage of the carrier

terminal.

11.9 Erection of PLCC and associated equipment


The installation should be done as per planned system. The equipment

allocated for a particular section/ station should not be diverted. This

may result in complications at a later stage because of crowded carrier

spectrum.

The Power Line Carrier Communication Equipments are basically

divided into two groups; viz:-

i) Outdoor equipments and

ii) Indoor equipments

11.9.1 Outdoor equipments


i) Line Trap

a) Suspension Mounted

The main Line Trip coil and the Tuning Pot/Lightning Arrester

are supplied separately. Generally before raising the Line Trap

for hanging from the gantry the Tuning Pot and Lightning

Arrester must be installed and connected. The Line Trap should

be hung from the gantry with the help of the insulating string and

ball and socket joint. The necessary clamps for hanging the Line

Trap from the gantry are as under:-

Ball and Socket arrangement for connecting the insulator

string to the central rod of the Line Trap;

Flat pad Aluminium clamp for connection of the Line Trap

incoming terminal to ACSR Jumper;

Flat pad Aluminium clamp for connecting Line Trap outgoing

terminal to station equipment.

The Line Trap is suitable for outdoor pedestal or suspension

mounting and should be mechanically strong enough to

withstand the stresses due to maximum specified wind pressure.

b) Pedestal Mounted

For pedestal mounting, each line trap shall be mounted on a

tripod structure formed by three insulator stacks arranged in a

triangular form. All the accessories and hardware, mounting

stool including bolts for fixing the line trap on insulators are of

non-magnetic material.

Terminal connectors may be welded with the Traps or it may be

supplied separately also depending upon the manufacturer. The

conductor take off (Horizontal or Vertical) from the Line Trap

should be ensured as indicated in the Line Trap drawings if the

Line Trap is to be connected with 4” IPS pipe . Generally it is not

possible to connect the pipe directly on the Line Trap.

ii) Coupling Device

The coupling device is interposed between the capacitor voltage

transformer and coaxial line to the PLC transmitter/receiver, and

in conjunction with the capacitor voltage transformer to ensure:

Efficient transmission of carrier frequency signals between

the carrier frequency connection and the power line.

Safety of personnel and protection of the low voltage parts

and installation, against the effects of power frequency

voltage and transient over voltages.

For direct and efficient earthing of its primary terminals, the

coupling device is equipped with an earthing switch. The Earth

Switch is available for earthing of CVT-HT terminals, when the

coupling filter units are removed from circuit for

maintenance/replacement.

The coupling device is suitable for outdoor mounting. All the

elements of coupling device are fitted on a base plate having

pad locking arrangements. The HT Terminals of coupling device

is connected to H.F. Terminal of the CVT by means of copper

wire of specified size with suitable lugs & taped. The impedance

points available on coupling device should be checked with

respect to available H.F. cable impedance. The H.F. point of

CVT on which coupling device is not mounted must be earthed.

Other two CVTs are earthed through coupling device.

iii) Earth Switch

The Coupling Device is earthed through this earth switch during maintenance.

11.9.2 Indoor equipments


i) Telephone Equipment

The telephone equipment is either housed in the same steel

cabinet which is used for housing the carrier set or in a separate

steel cabinet. If the equipment is housed in a separate steel

cabinet, the cabinet should be mounted on concrete plinth or

steel structure will depend upon the dimensions of the cubicle

housing telephone equipment.

ii) Interconnection Cables

Various types of Interconnection Cables are required for

connecting the Indoor Equipment. The Cables which are

required for power Line Carrier Communication Equipment are

indicated hereunder for general guidance:-

a) Power Supply Cables

Standard 3 core PVC cable is used for connection between the

power supply point and the Float Charger. The cable length can

be decided depending upon the position of the Float Charger.

Interconnection between Float Charger & Battery/Carrier

Equipment and Telephone Equipment requires 48V DC supply 3

Core PVC cable. The cross section of the cable to be used will

depend upon the current rating and the distance of the

equipment from Battery/Float Charger. The length of the cable

will depend upon the layout of the Substation and the position of

the Carrier Room, Distribution Board, Battery Room etc.

The PLCC equipment is operated, on 48 V DC supply. Normally

battery charger feeds the load and trickle charges the Battery.

In the event of AC failure the battery feeds the load. Further

looping of power supply may be done at PLCC panels ends.

b) Co-axial Cable

The outdoor Co-axial Cable is used for connecting the Line

Matching Units/Line Matching & Distribution Units/Coupling

Filters/Balancing Transformers and the Carrier Sets. Armoured

H.F. cable should be used. The Co-axial Cable can be directly

buried in the ground; however, it is preferable to provide suitable

trench from out-door switchyard to the carrier room to lay the

Co-axial Cable.

Proper Co-axial Cable connections is one of the most important

tasks and the connection of the Co-axial Cable to the Cable

Connector Plug should be done carefully, as per the special

instructions attached. While cutting the Co-axial Cable it should

be noted that at least 1 mt. extra length should be foreseen in

order to avoid cable joints due to minor modifications or due to

waste while connecting the Co-axial Cable to the Cable end

connectors.

Till the time the Co-axial Cable ends are not connected to the

Co-axial Cable connector these must be sealed by tar to avoid

ingress of moisture, which is harmful to the Co-axial Cable.

iii) Connection of Co-axial cable

The connection of the C0-axial Cable to the Cable end Socket or

to the Cable connector plugs in the Cabinet must be executed

according to the attached connection instructions.

Line trap is provided with a protective device in the form of surge

arresters which is designed and arranged such that neither

significant alteration in its protective function nor physical

damage shall result from either temperature rise or the magnetic

field of the main coil at continuous rated current or rated short

time current.

The protective device does neither enter into operation nor

remain in operation, following transient actuation by the power

frequency voltage developed across the line trap by the rated

short time current. The protective device is shunt connected to

the main coil and tuning device.

The lightning arrester is of station class current limiting active

gap type. Typically its rated discharge current is 10 kA.

Line traps are equipped with the bird barriers as specified.

iv) Jumper Connections

The overhead conductor is connected by jumpers to the wave

trap by using T- Clamps. These connectors are an integral part

of the line trap.

v) General

All Indoor equipment should be housed in a well ventilated room

having dust free atmosphere.

If the Cabinets are mounted in rows, the distance between the two

rails (face to face) should be at least 2 to 3 mtrs. for easy

maintenance/testing of the equipment.

11.10 Connection of HF Co-Axial Cable


Instructions for connecting Cable Connector Plugs to HF Co-axial

Cable.

i) Cut off the cable somewhat longer than needed(according to local

conditions), leaving enough slack to make a loop when connecting

the cable.

ii) Loosen the screw and take the plug to pieces.

iii) Put the cone and threaded cylinder over the cable

iv) Remove PVC-covering and copper braiding for a length of 20 mm

(4/5 inch)

v) Cut off PVC covering for an additional length of 6 mm (1/4 inch)

vi) Slightly spring open the split section of the plug interior

vii) Push the cable into the spring opening of the above part

viii)Draw the copper braiding through the two holes in the plug interior

piece and solder it to the outside of the plug interior piece

ix) Solder the cable conductor to the plug pin and cut off the part which

protrudes. (Do not heat the pin too long because of the

polyethylene insulation)

x) Slide the threaded cylinder and the cone back into position and

tighten the screw

xi) Test cable for continuity and short circuit

xii) Fasten the cable beneath the connector plug by means of bracket

clip, so that the plug is not subjected to any tension.

11.11 Installation of Equipment as per planned system


Installation should be done as per planned system. The equipment

allocated for a particular section should not be diverted. This may result

in complications at a later stage because of crowded carrier spectrum.

11.12 Defective Modules and Fault Rectification at Site


The defective modules of PLCC equipment are generally repaired at

suppliers works unless the nature of defects are minor. It is desired

that following procedure may be followed while returning the defective

modules to supplier:

i)After identification of defective modules, a small label/paper sticker

can be pasted on the module frame with “module defective” indication.

This helps in identifying the defective parts. Writing by pen or any

scratches on the module should be avoided. It would be advisable to

give the details of the part failures observed by the maintenance

persons for easy checking and rectification.

ii)After identification of the defective modules, these should be securely

packed with adequate packing material to avoid transit damage.

iii)It is desired that the cabinet nos. of the PLC terminal should be

intimated to the supplier/kept in record while sending the defective

modules. This will enable quick replacement after receipt of modules

duly repaired.

iv)Frequency dependent parts viz., filters are normally under long

guarantee. The modules require accurate adjustment which in turn

require sophisticated/accurate measuring set up. Therefore, it is

essential that these modules are returned to supplier immediately after

they are found defective, without any efforts to repair them at site.

DO’S DON’TS&

SPECIAL PRECAUTIONS



i) All the welding included in the manufacture of line traps should be

performed by personnel and procedure qualified in accordance with

ASME-IX and all the critical welds should be subject to tests as per

FQP/LOA as applicable.

ii) Terminal Connectors should conform to IS: 5561.

iii) Terminal connectors for ACSR single/twin bundle conductor should

be suitable for either horizontal or vertical take-off of the conductor.

iv) No part of clamp or connector (including hardware) should be of

magnetic material.

v) All castings of terminal connectors should be free from blow holes,

surface blisters, cracks and cavities. All sharp edges shall be

blurred and rounded off.

vi) Connections of line trap should not foul with any other equipment.

vii) H.F. cable joints should be avoided to the extent possible.

viii)Amphenol type of terminals should be used for H.F. connections.

ix) The unbalanced HF cable should be earthed at PLC equipment end

only.

x) The balanced HF cable should be earthed at both ends.

xi) The line traps are packed in wooden crates rectangular in shape

and should always be positioned in their vertical state.

xii) In pedestal mounted traps, the pedestal with its associated

components is normally fixed to the trap. For proper stability,

pedestal may be apportioned to the top end of the packing crate.

xiii)Line trap should be shifted to erection site very carefully so as to

avoid transportation damage.

xiv)Line trap should be mounted on the support insulator pedestal and

bolted properly. Crane or derrick arrangement should be used for

this purpose.

xv) Level of the pedestal on 400 kV BPIs is to be checked carefully and

grouting bolts should be tightened properly with the required torque.

xvi)The body & the internal parts of the line trap should be handled

carefully to avoid any damage while placing it on the erected

insulator pedestal.

xvii)For all copper connections flat Copper strip of specified size is to

used. The connections from H.F. point of the Coupling Capacitor to

the 3-Elements of the Protective and to the Line Matching

Units/Line Matching & Distribution Units/Coupling Filters/Balancing

Transformers should be completed as per Drawing.

xviii) While completing the copper connection one should ensure that

the copper strip connections must be properly tinned by brazing

stove and thereafter the same should be painted to avoid rusting or

oxidation due to moisture.

xix)As suspension hardware is arranged by the erection contractor,

care should be taken so that the same is available before the

erection work.

xx) Before erecting the blocking band of Line Traps are to be checked

with respect to requirement of the line.

xxi)For interconnection between Protection equipment and Relay Panel

the cable required is 10/20 core 1 mm dia Control Cable. The

length of the cable will depend upon the distance between the

Protection equipment cubicle and the relay panel of the distance

protection relay.

xxii)For interconnection between AF shift channel to line

unit/teleprinters cable required is 0.6 mm dia, 5-pair telephone

cable.

xxiii)For interconnection between Carrier set and 4-Wire Group

Selector/PAX housed in separate cabinet the cable required is

10/20 - pair 0.6 mm diameter cable.

xxiv)For interconnection between PAX and Telephone instrument the

cable required is 0.6 mm dia. 10 pair/20 pair or even one pair/2

pair/5 pair telephone cables, depending upon the positions and

number of the Telephone Instruments to be connected to the PAX.

CHECK FORMAT

11.14 Check Format


1. Physical verification of different items done as per specifications,challans, BOQ, MICC etc.

Yes/No

2. All parts have been checked for any physical damage,discrepancy etc.

Yes/No

3. In case of any damage/discrepancy same has been reported tosupplier/insurance agency.

Yes/No

4. Corona ring for 400 kV WT has been fitted before lifting the samefor erection.

Yes/No

5. Suspension hardware for WT has been arranged by erectioncontractor before start of erection.

Yes/No

6. Blocking bands of line trap have been checked w.r.t.requirements of the line.

Yes/No

7. Protective earthing of PLC terminals and panels with thesubstation earthing has been done.

Yes/No

8. All hardware accessories, mounting stools including bolt/nuts forfixing Line Trap and insulators are of non-magnetic material.

Yes/No

9. Impedance point available on coupling device has been checkedwith respect to available HF cable impedance.

Yes/No

10. H.F. point of CVT on which the coupling device is not mountedhas been earthed.

Yes/No

11. The remaining, two CVTs have been earthed thro’ couplingdevice.

Yes/No

12. Conductor take off from line trap has been checked up with theLine Trap Drawings.

Yes/No

13. Connection of Co-axial cable to the cable connector plug hasbeen done carefully as per the specified instructions.

Yes/No

14. About 1m. extra length of Co-axial cable has been providedbefore cutting.

Yes/No

15. Co-axial cable ends are kept sealed to avoid ingress of moisturetill the time these are not connected to the cable connector.

Yes/No

16. All indoor equipments are housed in a well lit/ventilated and dustfree room.

Yes/No

17. Proper face to face distance of cabinets inside the PLCC room ismaintained between the two rails for maintenance/testing ofequipments.

Yes/No

18. All suspension hardware to be arranged by the erectioncontractor have been made available before the erection work.

Yes/No

19. While completing the copper connections it has been ensuredthat the copper strip connections are properly tinned bybrazing stove and same have been painted to avoid rusting oroxidation due to moisture.

Yes/No

CHAPTER-12CABLES

___________________________________________________________________________ CHAPTER

TWELVE___________________________________________________________________________

CABLESBack to contents page

12.0 Introduction


The function of cables in the substation is to transfer power from

auxiliary loads and connecting control systems. Power cables are

manufactured with 1,2,3 or 4 crores. The conductor is either copper or

aluminium. The conductor may be either solid or stranded. Each core

of the cable is provided with insulation. The insulation may be of PVC

or XLPE. Over the core insulation, a sheath of PVC or plastic PVC tape

is provided. Protective covering and armour made up of plastic or steel

is provided over the sheath. The auxiliary power for substation

auxiliaries is supplied through underground cables. The power cables

are used for various voltages upto 220 kV.

There are several types of power cables, depending on type of

insulation and configuration of conductors, shield, insulation, etc. Thus

a power cable is made up of the following basic components:

i) Conductor

ii) Core insulation

iii) Sheath (Inner/Outer)

iv) Protective covering and armouring.

Control cables are used in substations for connecting control systems,

measurement, signalling devices and protection circuits rated below

1000 V. They have a copper conductor. They may have another

rubber insulation or PVC insulation. Control cables have several cores,

each having independent insulation. To avoid interference due to stray-

magnetic fields, the control cables should be properly laid and their

sheaths should be properly earthed.

Control cables are used for protection circuits, communication circuits.

They are generally at low voltage (220 V AC, 110 V AC, 22048 V DC,

110 V DC, 48 V DC, etc.). Control cables are wired between the

control panels in the control room, and the various equipments in the

switchyard. The various measurements, protection, control

communication functions are dependent on control cables. The control

cables are also laid on cable racks inside the cable trenches.

12.1 Receipt, Inspection and Storage


i) Cable drums are procured in full drum length. In a typical

substation 1.1 KV grade power & control cables are procured in full

drum length of 500m +5%. These cable drums are issued to the

switchyard contractor for laying and connecting as per the approved

drawings.

ii) Cable drums should be unloaded with cranes/chain pulley blocks to

prevent any damage.

iii) The drums should be checked with the LOA, GR and MICC for the

serial no., length, size and make.

iv) In case of any discrepancy in size or visible damage to the cable,

matter should be immediately brought to the notice of the supplier

at the earliest.

v) Drums after visual inspection should be stored preferably in the

covered area. In case these are stored in open, proper care and

security should be provided to avoid theft/damage to the cable.

vi) The cable accessories and hume pipes are supplied by the

switchyard contractor. Site should check these items for any

damage, discrepancy in size and material.

12.2 Cable Laying in Switchyard


Cable laying in switchyard is done by following 2 methods.

i) Cable laying in underground (buried trenches).

ii) Cable laying in cable trays.

12.2.1 Cable laying in underground (buried trenches)


The cable trench in which the cable is to be buried under the ground

excavated upto the required depth of 1 to 1.2 m or as specified. The

bottom of the trench is levelled, freed from stones and sharp edges of

rock. A layer 10 cm thick of clean sand is laid at the bottom of the

trench. After laying the cable, it is covered with a 10 cm thick layer of

sand, where the soil conditions are not good. In other cases soft earth

may be used instead of sand. The remaining gap is filled with soft soil

and a layer of bricks is usually provided for protection against

mechanical damage and for identification of the cable route.

In case the cable is laid in pipes, the pipes may be of ceramic/cast

iron/galvanised iron/cement/PVC or as per specified material and size.

These are used for crossing streets or under railways tracks. The size

should be sufficiently large to put in additional cables later if required

so that the cables can be drawn out and replaced without disturbing the

earth above.

Cable markers/joint markers at the specified distance enroute the

cable trenches should be provided for cable tracing & direction.

12.2.2 Cable laying in cable trays


i) Cables should be laid as per approved drawings and schemes

ii) The cable laying and termination schedule should be checked at

site w.r.t. actual conditions. This will facilitate in checking the

complete coverage of various approved schemes and termination.

iii) A cable laying schedule is prepared based on which the size of

cable required for various equipments is calculated. The lengths of

the cables are also checked at site by actually measuring and

necessary changes should be incorporated in the drawings.

iv) The length of cable actually required should be more than the

actually measured to take care of cable termination in terminal

blocks.

v) More length will also help in future to take care of cable faults, when

some cable is required to be cut and cable joint is provided.

vi) The erection contractor based on the actual physical measurements

and drawings prepares a cable cutting schedule. The cable cutting

schedule is prepared to optimise the cable lengths and minimise

wastage.

vii) For pulling the cables from drums, rollers are used by placing at

about 2 m spacing.

viii)Power and control cables are secured to the separate cables trays.

The cable trays carrying power trays are on top tiers whereas the

control cables are laid in the trays below.

ix) Other cables like coaxial cables are laid separately from power and

control cables.

x) The power cables are fixed on trays. A clearance of 2d(where d =

dia of cable) is maintained from centre to centre.

xi) To minimise any damage to cable, the cable ends should be

sealed.

xii) Proper cable tags for identification should be tied to the cable. The

information like cable number, size, length, origin & termination

point of cable are to be punched on these tags.

xiii)Concrete or steel pipes that are buried at 1 to 1.2 m level below the

ground (or as specified) should be laid and cable should be made to

pass through these in case the cable crosses the drains, roads or

rail track.

xiv)All the cable trays, racks & metallic ducts should be grounded by

connecting at each end to earth-mat. The section of cable trays

should be bridged by copper (or as specified material) jumpers to

retain continuity of earthing.

12.3 Cable Termination


i) The cable termination work comprises of fixing, providing clumps,

cutting, drilling, fitting and other plumbing works.

ii) A cable termination schedule is prepared before starting the cable

termination.

iii) Cables are checked for continuity before the termination work.

DO’S DON’TS&

SPECIAL PRECAUTIONS

12.4 Do’s Don’ts and Special Precautions


i) Ensure that the cable trench work is complete in all respects and

the trenches are clean.

ii) Ensure that earth flat running is complete and all welding work

inside the trench is completed.

iii) During unreeling, laying and termination of cables, sufficient care

should be taken to avoid damage to the cables because of twist,

kink, sharp bend etc.

iv) Cables should be securely fixed to the cable trays.

v) Whenever it is required to bend the cable care should be taken so

that the standard permissible limits for bending are not crossed.

a) Control cables (1.1 kV) should not be bent below a

radius of 10x d

b) Power cables (1.1 kV) should not be bent below a

radius of 12x d (where d = dia of the cable)

i) Each cable and conduit run should be tagged with numbers that

appear in the cable and conduit schedule.

ii) The tags should be of aluminium with the number punched on it and

securely attached to the cable conduit by not less than two turns.

Cable tags should of rectangular shape for power cables and of

circular shape for control cables.

iii) The underground cable markers should project 150 mm above

ground and spaced at an interval of 30 meters. They shall be

located on both sides of road and drain crossings and also at every

change in direction.

iv) Cable tags should be provided inside the switchgear, motor control

centres, control and relay panels etc. wherever required for cable

identification, where a number of cables enter together through a

gland plate.

v) For drilling of gland plates holes should not be made by gas cutting.

vi) Double compression type nickel plated (coating thickness not less

than 10 microns) brass cable glands are provided by the Contractor

for all power and control cables to facilitate dust and weather proof

termination.

vii) The cable glands should comprise of heavy duty brass casting,

machine finished and nickel plated, to avoid corrosion and

oxidation. Rubber components used in cable glands should be of

neoprene and of tested quality.

viii)The cable (power and control) between LT station, control room,

DG set building and fire fighting pump house should be laid in the

buried cable trenches. In addition to the above, for lighting purpose

also, buried cable trench can be used in outdoor area.

ix) Cable route and joint markers and RCC warning covers should be

provided wherever required. The voltage grade of cables should be

engraved on the marker.

x) Cable should be laid on cable racks, in built-up trenches, vertical

shafts, excavated trenches for direct burial, pulled through pipes

and conduits laid in concrete ducts, run bare and clamped on

wall/ceiling/steel structures etc. as shown in the drawings.

xi) Cable racks and supports should be painted after installation with

two coats of metal primer (comprising of red oxide and zinc

chromate in a synthetic medium) followed by two finishing coats of

aluminium paint.

xii) Cables should be generally located adjoining the electrical

equipment through the pipe insert embedded in the floor.

xiii)In the case of equipments located away from cable trench either

pipe inserts should be embedded in the floor connecting the cable

trench and the equipment or in case the distance is small,

notch/opening on the floor should be provided. In all these cases

necessary bending radius as recommended should be maintained.

xiv)Cabling in the control room should be done on ladder type cable

trays.

xv) Cables from the equipment to trench should run in GI conduits.

xvi)Flexible conduit should be used between fixed conduit/cable trays

and equipment terminal boxes, where vibration is anticipated.

xvii)Power and control cables should be laid in separate tiers. The

order of laying of various cables should be as follows, for cables

other than directly buried.

xviii)Power cables on top tiers.

xix)Control instrumentation and other service cables in bottom tiers.

xx) Metal screen and armour of the cable should be bonded to the

earthing system of the station, as per the approved

drawings/schemes.

xxi)Rollers should be used at intervals of about two metres while pulling

the cables.

xxii)All due care should be taken during unreeling, laying and

termination of cable to avoid damage due to twist, kinks, sharp

bends, etc.

xxiii)Contractor should remove RCC/Steel trench covers before taking

up the work and replace all the trench covers after the erection-

work in that particular area is completed or when further work is not

likely to be taken up for some time.

xxiv)Contractor should furnish report on work carried out in a particular

week/specified period indicating cable numbers, date on which laid,

actual length and route, testing carried out, termination carried out

in the specified no. of copies.

xxv)Tray identification no on each run of trays at an interval of 10 m

should be painted.

xxvi)In case the outer sheath of a cable is damaged during

handling/installation, the same should be repaired to the satisfaction

of the site. In case any other part of a cable is damaged, the same

should be replaced by a healthy cable.

xxvii)Cable drums should be unloaded, handled and stored in an

approved manner and rolling of drums should be avoided as far as

possible.

xxviii)Control cable cores entering control panel/switchgear/MCB/

MCC/ miscellaneous panels should be neatly bunched, clamped

and tied with nylon strap or PVC perforated strap to keep them in

position.

xxix)Tag/ferrule on control cable cores at all termination should be

provided as per specification. In panels where a large number of

cables are to be terminated and cable identification is difficult, each

core ferrule should include the complete cable number as well.

xxx)Spare cores should be similarly tagged with cable numbers and

coiled up.

xxxi)Cable entry points should be sealed and made vermin and dust

proof and unused openings effectively closed.

xxxii)Solderless crimping of terminals should be done by using

corrosion inhibitory compound.

xxxiii) All cable termination should be appropriately tightened to ensure

secure and reliable connections. All the exposed parts of cable

lugs should be covered. with tape, sleeve or paint.

CHECK FORMAT



(Preferably with crane) to unload the packages.Yes/No

2. All items have been checked with the packing list, MICC,Challans GR etc.

Yes/No

3. After unloading the visual inspection of the packings has beencarried out along with the erection contractor and preferablywith the manufacturer of the equipment.

Yes/No

4. Cable drums have been unloaded with crane/chain pulleyblock to prevent any damage.

Yes/No

5. Drums have been checked for quantity and damage to cable. Yes/No

6. Cable in underground (buried trenches) have been buriedunder the ground upto the required depth of 1 to 1.2 m.

Yes/No

7. Cable has been laid and all civil works performed as per thetechnical specifications.

Yes/No

8. Crossing of roads, rail tracks has been done in theceramic/cast iron/GI/ Cement pipe of specified size.

Yes/No

9. Cable markers/joint markers have been pointed at thespecified distance enroute the cable trench for cable tracingand direction.

Yes/No

10. Cable in cable trenches have been laid as per approveddrawings.

Yes/No

11. Length of cable actually required is more than the measuredare to take care of cable termination in terminal block andcable faults in future.

Yes/No

12. Cable laying and termination schedule has been prepared asper the actual site conditions and actual measurements.

Yes/No

13. Cables are being laid as per approved cable laying schedule. Yes/No

14. A cable cutting schedule has been prepared to optimise thecable lengths.

Yes/No

15. Cables are being pulled from drums on rollers. Yes/No

16. Power and control cables are laid on separate cable trays. Yes/No

17. Co-axial cable is laid separately from para & control cable. Yes/No

18. A clearance of 2d (where d= dia of cable) is maintained fromcentre to centre.

Yes/No

19. Cable ends have been sealed to minimise any damage. Yes/No

20. All cable trays, racks and metallic ducts have been groundedby connecting each to earth/met.

Yes/No

21. Sections of cable trays have been bridged by copper jumpersto retain continuity of earthing.

Yes/No

CHAPTER-13CONTROL & RELAY PANELS

___________________________________________________________________________ CHAPTER

THIRTEEN___________________________________________________________________________

CONTROL AND RELAY PANELSBack to contents page

13.0 Introduction


A substation control room has following provisions and functions:

Metering and instrumentation

Tap-changer control and control of shunt capacitors for voltage

control.

Normal switching function from control room.

Protection of transmission lines, busbars, transformers, reactors,

circuit breakers, auxiliaries etc. in the event of abnormal conditions

such as faults.

Voice communication with neighbouring power stations and

substations by PLC (Power Line Carrier).

The various control panels, protection panels, PLC communication

panels, etc. are housed in the control room building of the substation.

The relay and control panels are located mainly in the control room of

the substation building from where it is possible to supervise and

monitor the substation. The substation can also be provided with

equipment allowing remote control from another substation or load-

despatching centre. The control room has the following panels

depending upon the local needs:

Control panels for individual feeder.

Protective relay panels.

Synchronising panels.

Carrier communication panel.

Panel for recording instruments i.e. DR, EL & Fault Locator.

In addition to the above indoor panels, in the control room, the

following indoor equipments are installed in the main substation

building on one or more floors/ or in other separate buildings.

MCC ( Main Control)Panel

ACDB

DCDB

Fire-Fighting Control Board

Air Conditioning Control Panel

The ACDB panel in the substation feeds the auxiliary power to

switchyard equipments and township.

The other panel in control room are Emergency Lighting Distribution

Board for feeding the emergency lighting in and around control room.

13.1 Construction Features


i) The panels are free standing, floor (channel) mounting type and

comprise structural frames completely enclosed with specially

selected smooth finished, cold rolled sheet steel of specified

thickness with front sheet and door frames, sides, door, top and

bottom portions.

iii) All doors, removable covers and panels are gasketed all around

with neoprene gaskets.

iv) Ventilating louvers in the panels have screens and filters. The

screens are made of either brass or GI wire mesh.

v) Panels have base frame with smooth bearing surface which is fixed

on the embedded foundation channels/insert plate. Anti-vibration

strips made up of shock absorbing material are placed between

panel & base frame.

vi) Panels are provided with the gland plates at the bottom for cable

entry.

Construction wise the C&R panels can be divided in two types

13.2 Simplex Panel


Simplex panel consists of vertical front panel with equipment mounted

thereon and having wiring access from rear for control panel & either

front or rear for relay panels. In case of panels having width more than

800 mm, double leaf-doors are provided. Doors have handles with

either built-in locking or provided with padlock for closing/locking

facility.

13.3 Duplex Panel


Duplex panel are walk-in tunnel type comprising of two vertical front

and rear panel sections connected back-on-back by formed sheet steel

roof tie members and a central corridor in between. The corridor

facilitates access to internal wiring and external cable connections. In

case of number of duplex panels located in a row side by side, the

central corridor is aligned to form a continuous passage. Both ends of

the corridor are provided with double leaf doors with lift off hinges.

Doors have handles with built-in locking or provided with pad-locks

for closing/locking facility. Separate cable entries are provided for the

front and rear panels.

13.4 Receipt and Storage at Site


i) The C&R panels are generally transported in trucks to the site.

ii) Panels are transported in vertical position only.

iii) At site proper unloading arrangements preferably with crane or

chain pulling block are made.

iv) After unloading the visual inspection of the panels should be carried

out along with the erection contractor and preferably with the

manufacturer of the panels.

v) The panels, should be checked with the packing list, MICC,

Challans GR etc.

vi) In case of any discrepancy of the items from the above

documents/LOA, the same may be intimated to the manufacturer at

the earliest.

vii) Any type of damage to the panels during transportation or any

missing items should also be brought to the notice of the panel

supplier or the insurance agency (if required).

viii)The panels are sent to the erection site or in store if the site is not

ready for the erection. However, the panels should be repacked if

these are to be stored for long time. Panels are stored in vertical

position only.

13.5 Erection of Panels


i) The site where the panels are to be erected should be ready

actually before the panels are brought.

ii) The panels should be erected as per the approved general

arrangement drawings from POWERGRID.

iii) It should be checked that the foundation of the panel is ready in all

respect. The foundation frame should also be erected confirming to

the necessary drawings.

iv) The required level of the foundation/foundation frame etc. should be

checked very carefully before the erection work.

v) All the panels are to be checked for alignment, verticality etc. The

true level is checked using spirit level or water tube.

vi) The polythene cover provided by the manufacturer on the panels

should not be removed at the erection stage rather it should be

retained upto the commissioning stage so as to avoid the dust and

scratches on the panels.

vii) Earthing of panels is done by the erection contractor for connecting

it with switchyard earth mat.

13.6 Mounting on Panels


i) All equipments on (or in) the panels are mounted and completely

wired to the terminal blocks ready for external connections.

ii) Equipments are mounted such that removal and replacement can

be accomplished individually without interruption of service to

adjacent devices and the easy access is available without use of

special tools. Terminal marking on the equipment shall be clearly

visible.

iii) The centre line of switches, push buttons and indicating lamps are

not less than 750 mm/specified height from the bottom of the panel.

The centre lines of relays, meters and recorders are not less than

450 mm/specified from the bottom of the panel.

iv) The centre lines of switches, push buttons and indicating lamps is

matched to give a neat and uniform appearance. Like wise the top

lines of all meters, relays and recorders is matched.

13.7 Panel Internal Wiring and Equipments in Panels


i) Wiring provided between all electrical devices mounted and wired in

the panels and between the devices and terminal blocks for the

devices to be connected to equipment outside the panels is done by

the panel supplier.

ii) When panels are arranged to be located adjacent to each other, all

interpanel wiring and connections between the panels is carried out

internally.

iii) All the internal wiring is securely supported, neatly arranged, readily

accessible and connected to equipment terminals and terminal

blocks. Wiring gutters & troughs are used for this purpose.

iv) Auxiliary bus wiring for AC and DC supplies, Voltage Transformer

circuits, annunciation circuits and other common services is

provided near the top of the panels running throughout the entire

length of the panels.

v) Wire termination are made with solderless cirmping type and tinned

copper lugs which firmly grip the conductor. Insulated sleeves are

provided at all the wire termination’s. Engraved core identification

plastic ferrules marked to correspond with panel wiring diagram are

fitted at both ends of each wire.

vi) Longitudinal troughs extending throughout the full length of the

panels are preferred for inter panel wiring.

13.8 Providing Terminal Blocks


i) All internal wiring to be connected to external equipments is

terminated on terminal blocks, preferably vertically mounted on the

side of each panel.

ii) Terminal blocks are continuous current rating, moulded piece,

complete with insulated barriers, stud type terminals with washers,

nuts and lock nuts.

iii) Terminal blocks are suitable for connecting the following

conductors/ cable on each side:

a) All CT & PT/CVT circuits: (of specified sized cables).

b) AC/DC Power supply Circuits : (of specified sized cables).

c) All other circuits: (of specified sized cables).

iv) A minimum clearance of 250 mm/.as specified between the first

row of terminal blocks and the associated cable gland plate or

panel side wall, as per the Terminal block mounting

arrangement is adopted.

v) The clearance between two rows of terminal blocks edges

should be minimum of 150 mm.

vi) Mimic diagram is preferably made of anodised aluminium or

plastic of approved fast colour material and screwed on to the

panel that can be easily cleaned.

13.9 Name Plates and Markings


i) Inside the panels all equipment mounted on front and rear side as

well as equipment mounted inside are provided with individual

name plates with equipment designation engraved.

ii) On the top of each panel on front as well as rear side, large and

bold name plates are provided for circuit/feeder designation.

iii) All front mounted equipments are provided at the rear with

individual name plates engraved with tag numbers corresponding to

panel internal wiring to facilitate easy tracing of the wiring.

iv) The name plates mounted directly by the side of the respective

equipments should not be hidden by equipment wiring.

v) The name plate ‘inscription’ and size of name plates and letters

should be as approved by site Engineer.

13.10 Panels Accessories


i) Plug Point

240V, Single phase 50 Hz, AC socket with switch suitable to

accept 5 Amps and 15 Amps pin round standard plug, is

provided in the interior of each cubicle with ON-OFF switch for

connection of hand lamps.

ii) Interior Lighting

Panels are provided with a fluorescent lighting fixture rated for

240 Volts, single phase, 50 Hz supply for the interior illumination

of the panel during maintenance. The fittings is complete with

switchfuse unit and switching of the lighting is controlled by the

respective panel door switch. Adequate lighting with switchfuse

unit is also provided for the corridor in Duplex panels.

iii) Switches and Fuses

Control panels are provided with necessary arrangements for

receiving, distributing, isolating and fusing of DC and AC

supplies for various control, signalling, lighting and space heater

circuits. The incoming and sub-circuits are separately provided

with switchfuse units.

iv) Space Heater

Panels are provided with a space heater rated for 240V, single

phase, 50 Hz, AC supply for the internal heating of the panel to

prevent condensation of moisture.

13.11 Earthing


i) All panels are equipped with an earth bus securely fixed.

ii) When several panels are mounted adjoining each other, the earth

bus is made continuous with necessary connectors and clamps for

this purpose.

iii) Provision is made for extending the earth bus bars to future

adjoining panels on either side.

iv) Provision is made on each bus bars of the end panels for

connecting earthing grid.

v) All metallic cases of relays, instruments and panel mounted

equipment including gland plates are connected to the earth bus by

copper wires of specified size.

vi) The colour code of earthing wire is green.

vii) Soldering of earthing wire to terminals with suitable clamp

connectors is not permitted.

DO’S DON’TS&

SPECIAL PRECAUTIONS

13.12 Do’s Don’ts and Special Precautions


i) Panels should be completely metal enclosed & dust, moisture and

vermin proof.

ii) Workmanship of the panels should be such as to result in neat

appearance, inside and outside with no welds, rivets or bolt head

apparent from outside with all exterior surfaces tune & smooth.

iii) No equipment should be mounted on the doors.

iv) At existing station panels should be matched with other panels in

the control room in respect of dimensions, colour, appearance and

arrangement of equipments (centre lines of switches, push buttons

and other equipments) on the front of the panel.

v) Ferrules should fit tightly on the wire and not fall off when the wire is

disconnected from terminal blocks.

vi) Ferrules in cable should indicate the TB no. of both the ends.

vii) All wires directly connected to trip circuit breaker or device should

be distinguished by the addition of red coloured unlettered ferrule.

viii)Inter-connections to adjacent panels should be brought out to a

separate set of terminal blocks located near the slots of holes

meant for taking the inter-connecting wires.

ix) Arrangements should permit easy inter-connections of adjacent

panels at site and wires for this purposes should be looped and

bunched properly inside the panels.

x) Completeness and correctness of the internal wiring and the proper

functioning of the connected equipments should be checked by the

erection contractor.

xi) At least 20% spare terminals should be provided on each panel and

these spare terminals should be uniformly distributed on all terminal

blocks.

xii) When semaphore indicators are used for earth switch position they

should be so mounted in the mimic that the earth switch close

position shall complete the continuity of mimic.

xiii)Indicating lamp, one for each feeder, for each bus should be

provided on the mimic to indicate bus charged condition.

xiv)Control & Relay panels are to be checked with the schematic

drawings and Bill of Materials for proper mounting of various

equipments and relays.

xv) It should be ensured that the erection front is ready for taking up

the erection work.

xvi)Cable entries to the panels should be from the bottom and through

cable glands.

xvii)Cable gland plate fitted on the bottom of the panel should be

connected to earthing of the panel/station through a flexible braided

copper conductor rigidly.

xviii)Each instrument and meter should be prominently marked with the

quantity measured e.g. KV, A, MW, etc.

xix)All relays and other devices should be clearly marked with

manufacturer’s name, manufacture’s type, serial number and

electrical rating data.

xx) Each switch should bear clear inscription identifying its function.

CHECK FORMAT


1. All items have been checked with the packing list, MICC,Challans, GR etc.

Yes/No

2. After unloading the visual inspection of the panels has beencarried out along with the erection contractor and preferablywith the manufacturer of the panels.

Yes/No

3. Any type of damage to the panels during transportation or anymissing items has been brought to the notice of the panelsupplier.

Yes/No

4. In case of any discrepancy from the above documents/LOAthe same has been intimated to the manufacturer/ insuranceagency (as desired).

Yes/No

5. Proper unloading arrangement has been made at site tounload the panels.

Yes/No

6. Site where panels are to be erected is ready before thestarting of erection work.

Yes/No

7. The foundation frame has been erected and checked foralignment and level.

Yes/No

8. Panels during erection on frames have been checked for truelevel by spirit level.

Yes/No

9. Earthing of panels has been provided. Yes/No

10. Wiring on panels is complete upto terminal block Yes/No

11. Marking on the equipments is clearly visible. Yes/No

12. Equipments have been mounted for easy removal andreplacement.

Yes/No

13. Centre line of switches, push buttons indicating lamps is notat less than the specified height from the bottom of panel.

Yes/No

14. All internal wiring is securely supported, neatly arranged,readily accessible and connected to equipment terminals andterminal block

Yes/No

15. Wire termination are made with solderless crimping type andtinned copper lugs firmly gripping the conductor.

Yes/No

16. Proper minimum clearance between 2 rows of terminal blocksedges has been provided.

Yes/No

17. Mimic diagram has been properly screwed to the panel. Yes/No

18. Large and bold name plates have been provided forcircuit/feeder designation.

Yes/No

19. Name plates mounted by the side of respective equipmentsare not hidden by equipment wiring.

Yes/No

20. Proper sized inscription has been done on the name plates Yes/No

21. Each switch has been inscripted clearly identifying itsfunctions.

Yes/No

22. Fluorescent lighting fixtures have been provided for theinterior illumination in the panel

Yes/No

23. Heaters have been provided inside the panels to preventcondensation of moisture

Yes/No

24. All metallic cases of relays, instruments and panel mountedequipment have been earthed

Yes/No

___________________________________________________________________

BIBLIOGRAPHY

1. ASME Boiler and Pressure Vessel Code – Section-IX.

2. Rihand Delhi Bipole, HVDC Transmission System – POWERGRID.

3. Instruction for Erection of Power Line Carrier Communication and Associated

Equipments – M/s Asea Brown Boveri.

4. Electrical Substations Engg. & Practice – S. Rao.

5. Operation and Maintenance Manual for 216 KV Surge Arrestor – M/s

Crompton Greaves Limited.

6. Construction Manual Part-I substation Construction, Volume-III, Section III :

Switchyard Erection SRTS Powergrid.

7. Technical Specifications Volume-II of Bidding Document for Nathpa Jhakri

Transmission System – POWERGRID.

8. Installation and Service Manual for 420 KV Centre break Isolator by S&S

power Switchgear Ltd.

9. Modern power Station Practice (British Electricity International), Third Edition,

Volume K, EHV Transmission.

10. The Electrical Engineering Handbook, By Richard C. Dorf.

CONSTRUCTION MANAGEMENT DEPARTMENT

User’s ManualOf

Construction

Transmission Line(Part-1)

Sub-Station(Part-2)

General Support(Part-3)

Vol. 1Line Survey

Vol. 3Soil Investigation

& Foundation

Vol. 5Stringing

Vol. 2Env. Mgmt.

Vol. 4Tower Erection

Vol. 1Land &Infrastr.

Vol. 3Switchyard

Ercn.

Vol. 5Aux. Pkgs.

(Elect.)

Vol. 2Civil

Construction

Vol. 4Ercn. Of TF,

SR & CB

Vol. 1MB

(Procedures &G. Lines)

Vol. 3Contracts

Mgmt.

Vol. 5Labour

Regulations

Vol. 2Safety

Vol. 4Budget

& Finance

switch yard erection(2)

Documents