substation report

[A MODEL OF 220/132KV SUBSTATION] 2010-2011

Department of Electrical & Electronics Engineering |SATM Indore (M.P.) 1


Chapter 1

Introduction



1.1 Definition of Sub-Station:-

“The assembly of apparatus used to change some Characteristics (e.g. Voltage Ac to Dc freq.

p.f. etc) of electric supply is called sub-station”

The present day electrical power system is A.C. i.e., electric power is generated, transmitted

and distributed in the form of Alternating Current. The electric power is produce at the power

station, which are located at favourable places, generally quite away from the consumers. It is

delivered to the consumer through a large network of transmission and distribution. At many

place in the line of power system, it may be desirable and necessary to change some

characteristic (e.g. Voltage, ac to dc, frequency p.f. etc.) of electric supply. This is

accomplished by suitable apparatus called sub-station for example, generation voltage

(11KVor 6.6 KV) at the power station is stepped up to high voltage (Say220KVto 132 KV)

for transmission of electric power. Similarly near the consumer’s localities, the voltage may

have to be stepped down to utilization level. This job is again accomplished by suitable

apparatus called sub-station. Yet at some places in the power system, it may be desirable to

convert large quantities of a.c. power to d.c. power e.g. for traction, electroplating etc. This

job is again performed by suitable apparatus (e.g. ignitron) called sub-station. It is clear that

this type of equipment needed in a sub-station will depend upon the service requirement.

1.2. About Sub-Station

Sub-stations are important part of power system. The continuity of supply depends to a

considerable extent upon the successful operation of sub-station. It is therefore, essential to

exercise utmost care while designing and building a sub-station. The following are the

important points which must be kept in view while laying out a sub-station:

i) It should be located at a proper site. As far as possible, it should be located at the

centres of gravity of load.

ii) It should provide safe and reliable arrangement. For safety, considerations must be

given to the maintenance of regulation clearance, facilities for carrying out repairs and

maintenance, abnormal occurrences such as possibility of explosion or fire etc. For reliability,



consideration must be given to a good design and construction, the provision of suitable

protective gear etc.

iii) It should be easily operated and maintained.

iv) It should involve minimum capital cost.

1.2.1 Selection of Site: -

Main points to be considered while selecting the site for Grid Sub-Station are as follows:

i) The site chosen should be as near to the load centre as possible.

ii) It should be easily approachable by road or rail for transportation of equipments.

iii) Land should be fairly levelled to minimize development cost.

iv) Source of water should be as near to the site as possible. This is because water is

required for various construction activities (especially civil works), earthing and for

drinking purpose.

v) The Sub-Station site should be as near as to the town/city but should be clear of public

places, aerodromes, and military/police installations.

vi) The land should be have sufficient ground are to accommodate sub-station equipments,

buildings, staff quarters, space for future expansion.

vii) Set back distances from various roads such as National Highways, State Highways

should be observed as per as the regulations in force.

viii) While selecting the land for the sub-station preference to be given to the Govt. Land

over Private Land.

ix) The land should not have water logging problem.

x) Far away from obstructions, to permit easy and safe approach / termination of high

voltage overhead transmission lines.



1.2.2 Classification of Sub-Stations: -There are several ways of classifying them

according to (1) Service requirement and (2) Constructional features.

1) According to Service Requirement: - A sub-station may be called upon

change voltage level or improve power factor or convert a.c. power to d.c. power etc.

according to service requirement, sub-station may be classified as following:

i) Transformer Sub-Stations:- Those sub-stations which change the voltage level of

electric supply are called transformer sub-stations. These sub-stations receive power at some

voltage level and deliver it at some other voltage. Obviously, transformer will be the main

component in such sub-station. Most of the sub-station in the power system are of this type.

ii) Switching Sub-stations:- These sub-stations do not change the voltage level i.e.,

incoming and outgoing lines have the same voltage level. However, they simply perform the

switching operations of power lines.

iii) Power Factor Correction Sub-Stations:- Those sub-stations which improve the

power factor are called power factor correction sub-stations. Such sub-stations are generally

located at the receiving end of the transmission lines. These sub-stations generally use

synchronous condensers as the power factor improvement equipment.

iv) Frequency Changer Sub-Station:- Those sub-stations which change the supply

frequency are known as frequency change sub-stations. Such a frequency change may be

required for industrial utilization.

v) Converting Sub-Stations:- Those sub-stations which change a.c. power to d.c.

power are known as converting sub-stations. These sub-stations receive a.c. power and

conver it into d.c. power with suitable apparatus to supply for such purpose as traction,

electroplating, electric welding etc.

vi) Industrial Sub-Station:- Those sub-station which supply power to individual

industrial concerns are known as industrial sub-stations.



2) According To constructional Features: - A sub-station has many

components (e.g. circuit breakers, switches, fuses, instruments etc.) which must be housed

properly to ensure continuous and reliable service. According to constructional features, the

sub-stations are classified as:

i) Indoor Sub-Station:- For voltages upto 11 kV, the equipments of the sub-station is

installed indoor because of economic considerations. However, when the atmosphere is

contaminated with impurities, these sub-stations can be erected for voltages voltage upto 66

kV.

ii) Outdoor Sub-Stations:- For voltages beyond 66 kV, equipment is invariably

installed out-door. It is because for such voltages, the clearances between conductors and the

space required for switches, circuit breakers and the other equipments become so great that it

does not economical to install the equipment indoor.

iii) Underground Sub-Stations:- In thickly populated areas, the space available for

equipment and building is limited and the cost of land is high. Under such conditions, the

sub-station is created underground.

iv) Pole Mounted Sub-Stations: - This is an out-door sub-station with equipment

installed over-head on H-pole or 4-pole structure. It is the cheapest form of sub-station for

voltages not exceeding 11kV (33 kV in some cases). Electric power is almost distributed in

localities through such sub-stations.



Chapter 2

Equipments In A Sub-Station



The equipment required for a transformer Sub-Station depends upon the type of Sub-Station,

Service requirement and the degree of protectiondesired.220KV EHV Sub-Station has the

following major equipments.

2.1 Bus- Bar: - When a no. of lines operating at the same voltage have to be directly

connected electrically, bus-bar are used, it is made up of copper or aluminium bars (generally

of rectangular X-Section)and operate at constant voltage. The bus is a line in which the

incoming feeders come into and get into the instruments for further step up or step down. The

first bus is used for putting the incoming feeders in LA single line. There may be double line

in the bus so that if any fault occurs in the one the other can still have the current and the

supply will not stop. The two lines in the bus are separated by a little distance by a Conductor

having a connector between them. This is so that one can work at a time and the other works

only if the first is having any fault.

2.2 Insulators: - The insulator serves two purposes. They support the conductor (or bus

bar) and confine the current to the conductor. The most commonly used material for the

manufactures of insulators is porcelain. There are several type of insulator (i.e., pine type,

suspension type etc.) and there used in Su b-Station will depend upon the service

requirement.

2.3 Isolating Switches: - In Sub -Station, it is often desired to disconnect a part of the

system for general maintenance and repairs. This is accomplished by an isolating switch or

isolator. An isolator is essentially a kniff Switch and is design to often open a circuit under

no load, in other words, isolator Switches are operate only when the line is which they are

connected carry no load. For example, consider that the isolator are connected on both side of

a circuit breaker, if the isolators are to be opened, the C.B. must be opened first.



Bus-Bar (www.rolitemfg.com)

Insulator (www.insulator-best-b2b.com)

Isolating Switch (www.m0ukd.com)


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2.4 Circuit Breaker: - A circuit breaker is equipment, which can open or close a

circuit under normal as well as fault condition. These circuit breaker breaks for a fault which

can damage other instrument in the station. It is so designed that it can be operated manually

(or by remote control) under normal conditions and automatically under fault condition.

There are mainly two types of circuit breakers used for any substations. They are

• SF6 Circuit Breakers;

• Spring Circuit Breakers;

For the latter operation a relay wt. is used with a C.B. generally bulk oil C.B. are used for

voltage upto 66 KV while for high voltage low oil & SF6 C.B. are used. For still higher

voltage, air blast vacuum or SF6 circuit breaker are used. The use of SF6 circuit breaker is

mainly in the substations which are having high input kv input, say above 220kv and more.

The gas is put inside the circuit breaker by force i.e., under high pressure. When if the gas

gets decreases there is a motor connected to the circuit breaker. The motor starts operating if

the gas went lower than 20.8 bar. There is a meter connected to the breaker so that it can be

manually seen if the gas goes low. The circuit breaker uses the SF6 gas to reduce the torque

produce in it due to any fault in the line. The circuit breaker has a direct link with the

instruments in the station, when any fault occur alarm bell rings.

2.5 Protective Relay: - A protective relay is a device that detects the fault and

initiates the operation of the C.B. to isolate the defective element from the rest of the

system”. The relay detects the abnormal condition in the electrical circuit by constantly

measuring the electrical quantities, which are different under normal and fault condition. The

electrical quantities which may change under fault condition are voltage, current, frequency

and phase angle. Having detected the fault, the relay operates to close the trip circuit of C.B.

Most of the relay used in power system operates by virtue of the current and/or voltage

supplied by current and voltage transformer connected via various combinations to various

combinations to the system element that is to be protected. Through the individual or relative

changes in these two quantities, faults signal their presence, type and location to the



protective relays. Most of the relays in service on electric power system are of electro-

mechanical type. They work on the following two main operating principles:

1 Electromagnetic Attraction

2 Electromagnetic Induction

Different types of relays used in power system may be described as follows:

i) Latching Relay: - Latching relays are also called impulse relays. They work in the

bistable mode, and thus have two relaxing states. They are also called keep relays or stay

relays because as soon as the current towards this relay is switched off, the relay continues

the process that it was doing in the last state. This can be achieved only with a solenoid which

is operating in a ratchet and cam mechanism. It can also be done by an over-centre spring

mechanism or a permanent magnet mechanism in which, when the coil is kept in the relaxed

point, the over-centre spring holds the armature and the contacts in the right spot. This can

also be done with the help of a remanent core. In the ratchet and cam method, power

consumption occurs only for a particular time. Hence it is more advantageous than the others.

ii) Reed Relay: -These types of relays have been given more importance in the contacts.

In order to protect them from atmospheric protection they are safely kept inside a vacuum or

inert gas. Though these types of relays have a very low switching current and voltage ratings,

they are famous for their switching speeds.

iii) Polarized Relay: -This type of relay has been given more importance on its

sensitivity. These relays have been used since the invention of telephones. They played very

important roles in early telephone exchanges and also in detecting telegraphic distortion. The

sensitivity of these relays are very easy to adjust as the armature of the relay is placed

between the poles of a permanent magnet.



SF6 Circuit Breaker (www.kirloskar-electric.com)

Protective Relays (www.omron-ap.co.in)

Relay Panel (www.mclareunic.com)


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iv) Buchholz Relay: - This relay is actually used as a safety device. They are used for

knowing the amount of gas present in large oil-filled transformers. They are designed in such

a way that they produce a warning if it senses either the slow production of gas or fast

production of gas in the transformer oil.

v) Overload Protection Relay: -As the name implies, these relays are used to prevent

the electric motors from damage by over current and short circuits. For this the heating

element is kept in series with the motor. Thus when over heat occurs the bi-metallic strip

connected to the motor heats up and in turn releases a spring to operate the contacts of the

relay.

vi) Mercury Wetted Relay: -This relay is almost similar to the reed relay explained

earlier. The only difference is that instead of inert gases, the contacts are wetted with

mercury. This makes them more position sensitive and also expensive. They have to be

vertically mounted for any operation. They have very low contact resistance and so can be

used for timing applications. Due to these factors, this relay is not used frequently.

vii) Machine Tool Relay: -This is one of the most famous industrial relay. They are

mainly used for the controlling of all kinds of machines. They have a number of contacts with

easily replaceable coils. This enabkes them to be easily converted from NO contact to NC

contact. Many types of these relays can easily be setup in a control panel. Though they are

very useful in industrial applications, the invention of PLC has made them farther away from

industries.



viii) Contactor Relay: - This is one of the most heavy load relay ever used. They are

mainly used in switching electric motors. They have a wide range of current ratings from a

few amps to hundreds. The contacts of these relays are usually made with alloys containing a

small percentage of silver. This is done so as to avoid the hazardous effects of arcing. These

type of relays are mainly categorized in the rough use areas. So, they produce loud noises

while operated and hence cannot be used in places where noise is a problem.

ix) Solid State Relay: -SSR relays, as its name implies are designed with the help of

solid state components. As they do not have any moving objects in their design they are

known for their high reliability.

x) Solid State Contactor Relay: -These relays combine both the features of solid state

relays and contactor relays. As a result they have a number of advantages. They have a very

good heat sink and can be designed for the correct on-off cycles. They are mainly controlled

with the help of PLC, micro-processors or microcontrollers.

2.6 Instrument Transformer: - The line in Sub-Station operate at high voltage and

carry current of thousands of amperes. The measuring instrument and protective devices are

designed for low voltage (generally 110V) and current (about 5A). Therefore, they will not

work satisfactory if mounted directly on the power lines. This difficulty is overcome by

installing Instrument transformer, on the power lines. There are two types of instrument

transformer.

2.6.1 Current Transformer: - A current transformer is essentially a step-down transformer

which steps-down the current in a known ratio, the primary of this transformer consist of one

or more turn of thick wire connected in series with the line, the secondary consist of thick

wire connected in series with line having large number of turn of fine wire and provides for



measuring instrument, and relay a current which is a constant faction of the current in the

line. Current transformers are basically used to take the readings of the currents entering the

substation. This transformer steps down the current from 800 amps to1amp.This is done

because we have no instrument for measuring of such a large current. The main use of this

transformer is

a) Distance Protection;

b) Backup Protection;

c) Measurement.

2.6.2 Potential Transformer : -It is essentially a step–down transformer and step down the

voltage in known ratio. The primary of these transformer consist of a large number of turn of

fine wire connected across the line. The secondary way consist of a few turns and provides

for measuring instruments and relay a voltage which is known fraction of the line voltage.

2.7 Metering and Indicating Instrument : - There are several metering and

indicating Instrument (e.g. Ammeters, Volt-meters, energy meter etc.) installed in a

Substation to maintain which over the circuit quantities. The instrument transformers are

invariably used with them for satisfactory operation.

2.8 Miscellaneous Equipments: - In addition to above, there may be following

equipments in a Substation:-

i) Fuses

ii) Carrier -current equipment

iii) Sub-Station auxiliary supplies



Instrument Transformers

Current Transformer (www.audiovision.tradeindia.com)

Potential Transformer (www.kirloskar-electric.com)


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Metering And Indicating Equipments

(www.indiamart.com) (www.powerlinker.org)

(www.highvoltindia.com)


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2.9 Transformer: - There are three transformers in the incoming feeders so that the three

lines are step down at the same time. In case of a 220KV or more KV line station auto

transformers are used. While in case of lower KV line such as less than 132KV line double

winding transformers are used.

Autotransformer:

Transformer is static equipment which converts electrical energy from one voltage to another.

As the system voltage goes up, the techniques to be used for the Design, Construction,

Installation, Operation and Maintenance also become more and more critical. If proper care is

exercised in the installation, maintenance and condition monitoring of the transformer, it can

give the user trouble free service throughout the expected life of equipment which of the

order of 25-35 years. Hence, it is very essential that the personnel associated with the

installation, operation or maintenance of the transformer is through with the instructions

provided by the manufacture.

Basic principle of Transformer:

The transformer is based on two principles: firstly, that an electric current can produce a

magnetic field (electromagnetism) and secondly that a changing magnetic field within a coil

of wire induces a voltage across the ends of the coil (electromagnetic induction). Changing

the current in the primary coil changes the magnetic flux that is developed. The changing

magnetic flux induces a voltage in the secondary coil.

2.10 Line isolator: - The line isolators are used to isolate the high voltage flow through

the line into the bus. This isolator prevents the instruments to get damaged. It also allows the

only needed voltage and rest is earthed by itself.



2.11 Lightening Arrestors With Earth Switch: - lightening arrestors after the

current transformer are used so as to protect it from lightening i.e. from high voltage entering

into it. This lightening arrestor has an earth switch, which can directly earth the lightening.

The arrestor works at 30°to 45°angel of the lightening making a cone. The earth switch can

be operated manually, by pulling the switch towards ground. This also helps in breaking the

line entering the station. By doing so maintenance and repair of any instrument can be

performed.

2.12 Potential Transformers With Bus Isolators: - There are two potential

transformers used in the bus connected both side of the bus. The potential transformer uses a

bus isolator to protect itself. The main use of this transformer is to measure the voltage

through the bus. This is done so as to get the detail information of the voltage passing through

the bus to the instrument. There are two main parts in it

(a) Measurement;

(b) Protection;

2.13 Lightening Arrestors: - Firstly we can see lightening arresters. These lightening

arrestors can resist or ground the lightening if falls on the incoming feeders. The lightening

arrestors can work in a angle of 30 degrees around them. They are mostly used for protection

of the instruments used in the substation. As the cost of the instrument in the station are very

high to protect them from high voltage from lightening these lightening arrestors are used. It

is a device used on electrical power systems to protect the insulation on the system from the

damaging effect of lightning Metal oxide varistors (MOVs) have been used for power system

protection since the mid 1970s. The typical lightning arrester also known as surge arrester has

a high voltage terminal and a ground terminal. When a lightning surge or switching surge



travels down the power System to the arrester, the current from the surge is diverted around

the protected insulation in most cases to earth.

A lightning arrester is a single component in a lightning protection system. In

addition to rods placed at regular intervals on the highest portions of a structure, a lightning

protection system typically includes a rooftop network of conductors, multiple conductive

paths from the roof to the ground, bonding connections to metallic objects within the

structure and a grounding network. The rooftop lightning arrestor is a metal strip or rod,

usually of copper or aluminum. Lightning protection systems are installed on structures,

trees, monuments, bridges or water vessels to protect from lightning damage. Individual

lightning arrestors are sometimes called finials, air terminals or strike termination devices.

2.14 Wave Trap: - Wave trap also is known as Line trap. What it does is trapping the

high frequency communication signals sent on the line from the remote substation and

diverting them to the telecom/ teleprotection panel in the substation control room (through

coupling capacitor and LMU). This is relevant in Power Line Carrier Communication

(PLCC) systems for communication among various substations without dependence on the

telecom company network. The signals are primarily teleprotection signals and in addition,

voice and data communication signals. Line trap also is known as Wave trap. What it does is

trapping the high frequency communication signals sent on the line from the remote

substation and diverting them to the telecom/teleprotection panel in the substation control

room (through coupling capacitor and LMU). This is relevant in Power Line Carrier

Communication (PLCC) systems for communication among various substations without

dependence on the telecom company network. The signals are primarily teleprotection signals

and in addition, voice and data communication signals.



Lightning Arrestor (www.osha.gov)

Line Isolators (www.indiamart.com)


http://www.indiamart.com/

http://www.osha.gov/


Wave Trap / Line Trap (www.p-wholesale.com)


http://www.p-wholesale.com/


Transformer (www.electricalengineeringtour.blogspot.com)


http://www.electricalengineeringtour.blogspot.com/


The Line trap offers high impedance to the high frequency communication signals thus

obstructs the flow of these signals in to the substation busbars. If there were not to be there,

then signal loss is more and communication will be ineffective/probably impossible.

Basically, it is a tuned circuit placed in the antenna path to your rig, which traps and then

dissipates the signal, or at least a bunch of it, from a station, allowing you to reduce

interference between stations.



Chapter 3

Single Line Diagram



3.1 About Single Line Diagrams

Power systems are extremely complicated electrical networks that are geographically

spread over very large areas. For most part, they are also three phase networks – each power

circuit consists of three conductors and all devices such as generators, transformers, breakers,

disconnects etc. are installed in all three phases. In fact, the power systems are so complex

that a complete conventional diagram showing all the connections is impractical. Yet, it is

desirable, that there is some concise way of communicating the basic arrangement of power

system components. This is done by using Single Line Diagrams (SLD). SLDs are also called

One Line Diagrams.

Single Line Diagrams do not show the exact electrical connections of the circuits. As

the name suggests, SLDs use a single line to represent all three phases. They show the

relative electrical interconnections of generators, transformers, transmission and distribution

lines, loads, circuit breakers, etc., used in assembling the power system. The amount of

information included in an SLD depends on the purpose for which the diagram is used. For

example, if the SLD is used in initial stages of designing a substation, then all major

equipment will be included in the diagram – major equipment being transformers, breakers,

disconnects and buses. There is no need to include instrument transformers or protection and

metering devices. However, if the purpose is to design a protection scheme for the equipment

in the substation, then instrument transformers and relays are also included.

There is no universally accepted set of symbols used for single line diagrams. Often

used symbols are shown in Fig. 1. The variations in symbols are usually minor and are not

difficult to understand.

Concept of Bus

Concept of bus in single line diagrams is essentially the same as the concept of a node

in an electrical circuit. Just keep in mind that there is one bus for each phase. Buses are

shown in SLDs as short straight lines perpendicular to transmission lines and to lines

connecting equipment to the buses. In actual substations, the buses are made of aluminium or



copper bars or pipes and can be several meters long. The impedance of buses is very low,

practically zero, so electrically the whole bus is at the same potential. Of course, there is line

voltage between the buses of the individual phases.

3.2 Graphical Symbols For Single Line Diagrams

3.3 Bus-Bar Arrangements in Sub-Stations

Bus-bars are the important components in a sub-station. There are several bus-bar

arrangements that can be used in a sub-station. The choice of a particular arrangement

depends upon various factors such as system voltage, position of sub-station, degree of

reliability, cost etc. The following are the important bus-bar arrangements used in sub-

stations:



i) Single Bus-Bar System: - As the name suggests, it consist of a single bus-bar and all

the incoming and outgoing lines are connected to it. The chief advantages of this type of

arrangement are low initial cost, less maintenance and simple operation. However, the

principle disadvantage of single bus-bar is that if repair is to be done on the bus-bar or a fault

occurs on the bus, there is a complete interruption of supply. This arrangement is not used for

voltages exceeding 33 kV. The indoor 11kV sub-station often use single bus-bar

arrangement.

ii) Single Bus-Bar System with Sectionalisation: - In this arrangement the single bus-

bar is divided into sections and load is equally distributed on all the sections. Any two

sections of the bus-bar are connected by a circuit breaker and isolator. Two principal

advantage of this arrangement are, firstly, if a fault occurs on any section of the bus, that

section can be isolated without affecting the supply from other sections. Secondly, repairs

and maintenance of any section of the bus-bar can be carried out by de-energising that section

only, eliminating the possibility of complete shut down.

iii) Duplicate Bus-Bar System: - This system consist of two bus-bars, a “main” bus-bar

and a “spare” bus-bar. Each bus-bar has the capacity to take up the entire sub-station load.

The incoming and outgoing lines can be connected to either bus-bar with the help of a bus-

bar coupler which consists of a circuit breaker and isolators. Ordinarily, the incoming lines

remain connected to the main bus-bar. However, in case of repair of main bus-bar or fault

occurring on it, the continuity of supply to the circuit can be maintained by transferring it to

the spare bus-bar. For voltages beyond 33kV, duplicate bus-bar system is frequently used.



Fig. 3.3 a) Single Bus-Bar System



Fig 3.3 b) Single Bus-Bar System With Sectionalisation



Fig 3.3 c) Duplicate Bus-Bar System



3.4 Key Diagram of 220/132 kV Sub-Station



Chapter 4

Bibliography



Webliography

1. www.google.com

2. www.wikipedia.org

3. www.rolitemfg.com

4. www.kirloskar-electric.com

5. www.omron-ap.co.in

6. www.mclareunic.com

7. www.audiodivision.tradeindia.org

8. www.powerlinker.org

9. www.electricalengineeringtour.blogspot.com

10. www.p-wholesale.com

11. www.indiamart.com

Bibliography

1. A Course in Power Systems by J.B. Gupta (Chapter No. 17)

2. Electrical Power System by C.L. Wadhwa.

3. Principles of Power Systems by V.K. Mehta (Chapter No. 21,25)


substation report

Documents

substation substations

power station

substation site

substation equipments

definition of substation

substation preference

classification of substations

kv substation