training report summer 2012

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POWERGRID CORPORATION OF

INDIA LIMITED

765/400/220 kV WARDHA SUB STATION

TRAINING REPORT

SUB STATION OVERVIEWMay - June 2012

Submitted by:

Javvaji Krishna TejaElectrical and Electronics engineering

Visvesvaraya National Institute of

Technology, Nagpur.

Bachu RameshElectrical and Electronics engineering

Visvesvaraya National Institute of

Technology, Nagpur.


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POWERGRID CORPORATION OF

INDIA LIMITED

765/400/220 kV WARDHA SUB STATION

TRAINING REPORT

SUB STATION OVERVIEWMay - June 2012

Submitted by:

Rajan DubeyElectrical Engineering

Anjuman College of Engineering and

Technology

Akash Barse

Electrical EngineeringAnjuman College of Engineering and

Technology

Mohammad AsifElectrical Engineering

Anjuman College of Engineering and

Technology


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Index

Sr. No. Contents Page No.

1. Mission and Objectives of PowerGrid 5

2. Introduction of Wardha Substation 6

3 Single Line Diagram 7

4. Bus Switching Schemes 105. Lightning Arrester 12

6. Wave Trap 12

7. Current Transformer 13

8. Capacitive Voltage Transformer 14

9. Circuit Breaker 14

10. Isolator 16

11. Reactor 16

12. InterConnecting Transformer 18

13. Protection 19

14. Relay 21

15. Line/ Transformer/ Bus Bar Protection 23

16. Testing 24


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Acknowledgement:

We express with reverence our indebtedness to our guide Shri. PatanjaliSharma Sir, Chief Manager, Wardha Sub Station, for standing by us right from the

beginning of our training.

We are greatly thankful to the Shri. Nitin Bhoyar, Managerfor providing usan opportunity to do training work.

We express our sincere thanks to Shri. Kaushal Sir, Shinde Sir, Chimankarsir, Vinit Sir, Patnaik Sir, Patel Sir and each and every staff member for their

valuable advises and guidance to the training work.


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Mission Of PowerGrid

ESTABLISHMENT & OPERATION OF REGIONAL & NATIONAL POWER GRIDS TO

FACILITATE TRANSFER OF POWER WITHIN & ACROSS THE REGIONS WITH

RELIABILITY, SECURITY & ECONOMY ON SOUND COMMERCIAL PRINCIPLES

Objectives of Powergrid

To ensure requisite capital investment in power transmission sector by mobilizingresources on its own / through private participation.

To provide transmission system matching with generation capacity addition in the centralsector.

To augment and strengthen Regional Grids to and develop a strong National Grid tofacilitate exchange of power between Regions.

To extend the National Grid to a SAARC Grid by interconnecting neighboring countriesviz. Bhutan, Nepal, Bangladesh etc.

To Undertake diversification in synergic area of Telecommunication as a InfrastructureService Provider.

To assist state power utilities in Distribution Sector under Accelerated PowerDevelopment and Reforms Programme of the GOI.


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Introduction of Wardha SubStation:

This report is a brief description of 765kV/400kV/220kV substation at Wardha maintained

by Power Grid Corporation of India limited. It is located 16km away from Wardha at Deoli,

MIDC area. It is a transmission substation where power is taken from Seoni and transmitted toParli, Badnera, Maudha, MSEB etc. The future prospective of this substation is to have a

1200kV line.

Fig.1: Power map of Western Region


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Single Line Diagram

765KV


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220KV


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Bus Switching Schemes

Single Main Scheme Double Main Scheme Single Main & Transfer Scheme Double Main with by-pass isolator scheme Double Main & Transfer Scheme One & Half Breaker Scheme Double breaker Scheme Ring Bus Scheme

At wardha substation, we use one and half breaker schemefor 765/400 KV

lines and double main transfer schemefor 220KVlines.

One and half breaker scheme:

In this scheme, two circuit have three breakers, the middle breaker ties the two circuitsand hence is called the tie breaker.

Breaker or bus maintenance is possible without any shut down of the feeder Even if both the buses are out of service, power can be transferred from one feeder to

another feeder through tie breaker

Fig.2: One and half breaker scheme


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Double Main and Transfer Bus Scheme:

In this bus scheme, in addition to the two main buses there will be a separate transfer busalso.

Since separate transfer bus is available there will be no need of transferring the load fromone bus to the other bus unlike in a main cum transfer bus arrangement.

Fig.3: Double main transfer scheme overview


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Substation Equipments

Line equipment Lightning arrester Wave trap Transformer Reactor Capacitive voltage transformer Potential Transformer

Bay equipment Isolator Circuit Breaker Current transformer

Lightning ArrestersLightning Arresters need low resistance during flow of lightning current to limit surge

voltage and high resistance to limit discharge current.In wardha substation, the capacity of LA used for 765KV line is 624KV and that for

400KV is 390KV recently being replaced by 336KV.

.

Wave trapThe function of wave trap is to avoid high frequency signal to enter in the substation. It

allows only 50Hz signals to enter.

The capacities of wave traps used at wardha substation are 0.5mH, 1mH or 2mH.

Fig.4: 400kV lightening arrestor Fig.5: 400kv wave trap


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Current Transformer

The function of Current Transformer is same as that of step down transformer which step

down the high current to a measurable current.

At wardha substation, the CTs used are :

765KV: 3000/1 400KV: 2000/1 220KV: 1600/1

Types of CTs

Dead Tank Designo Hair Pin Designo Eye Bolt Design

Live tank Design

Fig.6: live tank current transformer Fig.7: Dead tank current transformer


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Capacitive Voltage Transformer

The function of CVT is: It steps down the high voltage level into low voltage/measurable level. In hot line communication like Power Line Carrier Communication through phase to

phase coupling device.At wardha substation the CVTs used are of 765/400/220 KV capacity.

Fig.8: 400kv capacitive voltage transformer

Circuit Breaker

Circuit breaker is an automatically operated electrical switch designed to protect an

electrical circuit from damage caused by overload or short circuit. Its basic function is to detect afault condition and, by interrupting continuity, to immediately discontinue electrical flow. Unlike

a fuse, which operates once and then must be replaced, a circuit breaker can be reset (eithermanually or automatically) to resume normal operation. Circuit breakers are made in varying

sizes, from small devices that protect an individual household appliance up to large switchgear

designed to protect high voltage circuits feeding an entire city.

TYPES OF CIRCUIT BREAKER

Fig.9:Usage of circuit breakers depending on voltage level


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Circuit-breakers lie at the heart of any switchgear installation.

Fig.10: Modes of operation of circuit breaker

Mode of operation

The current path is formed by the terminal plates [(1) and (8)], the contact support (2), the

base (7) and the moving contact cylinder (6). In closed state the operating current flows through

the main contact (4). An arcing contact (5) acts parallel to this.

Breaking operating currents

During the opening process, the main contact (4) opens first and the current commutates

on the still closed arcing contact. If this contact is subsequently opened, an arc is drawn betweenthe contacts (5). At the same time, the contact cylinder (6) moves into the base (7) and

compresses the quenching gas there. The gas then flows in the reverse direction through the

contact cylinder (6) towards the arcing contact (5) and quenches the arc there.

Breaking fault currents

In the event of high short-circuit currents, the quenching gas on the arcing contact is heated

substantially by the energy of the arc. This leads to a rise in pressure in the contact cylinder. In

this case the energy for creation of. the required quenching pressure does not have to be

produced by the operating mechanism. Subsequently, the fixed arcing contact releases the

outflow through the nozzle (3). The gas flows out of the contact cylinder back into the nozzleand quenches the arc.

The specific properties of the twin nozzle system are beneficial for restrike-free switching of low

inductive and capacitive currents. Thanks to its high arc resistance the system is especially

suitable for the breaking of certain types of fault such as those close to generators.


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Isolator

An isolator (UK terminology) or disconnector (US terminology) is a switch used to

isolate a section of a circuit from any energised conductors, by presenting a visible break in the

circuit. Isolators are not designed to break load currents (unless fitted with optional arc-breaking

feature) or to break fault currents.

Types of isolater

Type of Isolator Horizontal Centre Break Isolator (HCB) Horizontal Double Break Isolator (HDB) Pantograph Isolator (Panto) Vertical Break Isolator (VB) Knee type Isolator for 765kV Staggered

Knee type Isolator in close position

Fig.11: 765kv knee type isolator in close view

Reactor:

It is a simple shunt inductor or series capacitor installed to bring down the voltage at thereceiving end of a long transmission line, where the voltage is being boosted due the

Ferranti effect. It is line equipment, installed immediately at the incoming / outgoing ends after the

lighting arrestor and potential transformer in the line.

As the power is transmitted over long lines at high voltages the high capacitance of thetransmission line compared to its resistance and inductance will result in generation of

reactive power which ultimately results in boosting up of voltage at the receiving end ofthe transmission line.


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Thus, a shunt inductor or a series capacitor is installed at the line ends to consume thisreactive power generated along the transmission line and pull down the voltage to

appropriate level of transmission.

Reactors are generally installed on either side substations of the transmission lines , atappropriate ratings calculated as for the (each leg shunt capacitance) Pi-model of the

line.

The reactors used in wardha substation:

There are 10 single phase reactors and 5three phase reactors in wardhasubstation.

Among the ten single phase reactors 3 of them are used in incoming line of seoni-1 dia 3 of them are used in incoming line of seoni-2 dia 3 of them are used as bus reactors (maintains bus bar voltages) The other one is a spare reactor.

All 5three phase reactors are used in 400kv yard in different lines for the samepurposes as described.

Fig.12:a single phase reactor installed Fig.13:a three phase reactor installed

in 765kv yard at wardha substation in 400kv yard at wardha substation


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InterConnecting Transformer:

It is a static piece of device which is used for stepping down / stepping up of voltagelevels keeping power constant at a given frequency of operation.

It works on the principle of mutual induction It is line equipment installed at the incoming/outgoing ends of the line where ever a change

in voltage level is desired.

The use of transformer in the power system as lead to the reduction of generating costs andtransmission and distribution losses by providing a provision to have Generation at low voltage level ( economical) Transmission at high voltage (low losses) Distribution at low voltage ( to suit consumer requirements)Interconnecting Transformers used in wardha substation:

There are 10single phase and 3three phase interconnecting transformers in wardhasubstation

All the ten single phase transformers are auto transformers rated 765/400 kv, which areused to connect 765kv yard to the 400kv yard

3 of them are used in outgoing line of seoni-1 dia 3 of them are used in outgoing line of seoni-2 dia 3 of them are used in bus reactors dia The other one is a spare transformer.

All 3three phase transformers are star-delta-star transformers rated 400/33/220 kv,which are used to connect 400kv yard to the 220kv yard

The tertiary winding of the 3-phase transformer is to trap the third harmonic current. Inwardha substation, the tertiary winding of ICT1 in the 400kv yard is planned to be used

as a backup power source for substation equipment in future.

Fig.3:A single phase ICT installed Fig.4:A three phase ICT installedin 765kv yard at wardha substation in 400kv yard at wardha substation


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WHAT IS A PROTECTION?

Humans need protection from external disease, sun and whether. All the internal

parts of the human beings are protected naturally. Heart and lungs are protected by ribs bones

from external impact. Brain is protected by skull. Eyes are protected by eyelids and by closing

eyes. We need cloths to protect us from external environment conditions.

Similarly electrical equipment needs protection from any external or internal faults

which may produce a detrimental effect on it.

Electrical faults in the power system:

Transients Faults Permanent faults

Requirements of Protection System:

SENSITIVITY: The relay shall be sensitive to operate for minimum quantity ofoperating parameter.

SELECTIVITY: The relay/scheme should be able to select the faulty section andisolate.

SPEED: The relay should operate faster so that fault is isolated as fast as possible. RELIABILITY: The relay/scheme should operate for all types of faults with

repeatability and reliability. COST: The relay/scheme should be economical.


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ELEMENTS OF PROTECTION

CB

Feeder

Bus

CV

Relay

DC SOURCE

CT

Tri Ckt

Current

Voltage


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General Line Protection

Relay

A protective relayis an electromechanical apparatus, often with more than one coil,

designed to calculate operating conditions on an electrical circuit and trip circuit breakers when a

fault is detected. Unlike switching type relays with fixed and usually ill-defined operating

voltage thresholds and operating times, protective relays have well-established, selectable,

time/current (or other operating parameter) operating characteristics. Protection relays respond to

such conditions as over-current, over-voltage, reverse power flow, over- and under- frequency.

Distance relays trip for faults up to a certain distance away from a substation but not beyond that

point.

Objectives of Relay Protection

Protect persons and equipment in the surrounding of the power system. Protect apparatus in the power system. Separate faulty parts from the rest of the power system to facilitate the operation of the

healthy part of the system.

Types of Protective Relays

Overcurrent relay

An "overcurrent relay" is a type of protective relay which operates when the load current exceedsa preset value. The ANSI device number is 50 for an instantaneous overcurrent (IOC), 51 for atime over current (TOC). In a typical application the overcurrent relay is connected to a current

transformer and calibrated to operate at or above a specific current level. When the relay

operates, one or more contacts will operate and energize to trip (open) a circuit breaker.

Distance relay

The most common form of protection on high voltage transmission systems is distance relay

protection. Power lines have set impedance per kilometre and using this value and comparing

voltage and current the distance to a fault can be determined. The ANSI standard device number

for a distance relay is 21.

Current differential protection

Another common form of protection for apparatus such as transformers, generators, busses and

power lines is current differential. This type of protection works on the basic theory ofKirchhoff's current law which states that the sum of the currents entering and exiting a node will

equal zero. It is important to note the direction of the currents as well as the magnitude, as they

are vectors. It requires a set of current transformers (smaller transformers that transform currents


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down to a level which can be measured) at each end of the power line, or each side of the

transformer. The current protection relay then compares the currents and calculates the

difference between the two. As an example, a power line from one substationto another willhave a current differential relay at both substations which communicate with each other.

Static relays

Static relays with no or few moving parts became practical with the introduction of

the transistor. Static relays offer the advantage of higher sensitivity than purely

electromechanical relays, because power to operate output contacts is derived froma separate supply, not from the signal circuits. Static relays eliminated or reducedcontact bounce, and could provide fast operation, long life and low maintenance.

Numerical Protective Relays

The functions of electromechanical protection systems are now being replaced bymicroprocessor-based digital protective relays, sometimes called "numeric relays".

A microprocessor-based digital protection relay can replace the functions of many discrete

electromechanical instruments.

These convert voltage and currents to digital form and process the resulting measurements using

a microprocessor. The digital relay can emulate functions of many discrete electromechanical

relays in one device, simplifying protection design and maintenance. Each digital relay can run

self-test routines to confirm its readyness and alarm if a fault is detected. Numeric relays can also

provide functions such as communications (SCADA) interface, monitoring of contact inputs,metering, waveform analysis, and other useful features. Digital relays can, for example, store two

sets of protection parameters, which allows the behavior of the relay to be changed during

maintenance of attached equipment.

Basis of Classifications of Relays Quantity of response: Voltage, current, frequency, power etc. Function: Detection, time-delay, tripping, alarm, signaling, flag, contact multiplication Construction: Electromagnetic, Static or Numerical


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Transmission Line Protections

Distance Protection. SOTF. Over voltage Protection. VT Fuse fails. Power Swing Blocking. DEF Protection.

Transformer Protections

Differential Protection REF Protection Over flux protection Over current and Earth fault protection Mechanical Protections- PRV, Buchholz, WTI, OTI .

Bus Bar Protection

The Differential Current protection principle is used to protect the Bus Bars. Here thecurrent entering the bus and leaving the bus are summed up. The sum should be zero.

Bus Bar Scheme at Wardha S/sNumerical Distributed Bus Bar Scheme ( CU and PU)


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Testing in powergrid

FIELD TESTS

DEW POINT MEASUREMENT FOR LARGE TRANSFORMER FILLED WITH DRYAIR OR NITROGEN FILLED

WINDING RESISTANCE MEASUREMENT VECTOR GROUP AND POLARITY VOLTAGE RATIO TEST

MEASUREMENT OF MAGNETIZING CURRENT

MAGNETIC BALANCE TEST ON THREE PHASE TRANSFORMER INSULATION RESISTANCE MEASUREMENT MEASUREMENT OF CAPACITANCE AND DISSIPATION FACTOR

DISSOLVED GAS ANALYSIS ( DGA )

Pre Commissioning Tests

Polarity Test Magnetization Curve Test Ratio Test Primary Current Injection Test Secondary Current Injection Test

Trasformer oil testing

BDV( breakdown voltage) PPM(parts per million) Dissolved gas analysis Resistivity


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training report summer 2012

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