WBSETCL Subhash Gram 220KV Substation Training Report

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WBSETCL SUBHASH GRAM 220 KV SUB - STATION 19 TH JAN – 31 ST DEC 2015 SUBMITTED BY- ARIJIT BASU EE, DIPLOMA, 3 RD YEAR, BBIT

Transcript of WBSETCL Subhash Gram 220KV Substation Training Report

Page 1: WBSETCL Subhash Gram 220KV Substation Training Report

WBSETCL SUBHASH GRAM 220 KV SUB-STATION

19TH

JAN – 31ST

DEC

2015

SUBMITTED BY- ARIJIT BASU

EE, DIPLOMA, 3RD

YEAR, BBIT

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• WBSETCL• About the substation

• Bay arrangement• Single line diagram

• Receiving power• Step down of voltage• Sending power

• Phase to phase double channel system• Various frequencies of nearby substations

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Contents

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Introduction

West Bengal State Electricity Transmission Company Limited (WBSETCL) was set up in 2007 following the unbundling of the state electricity board of West Bengal.WBSETCL is the eleventh largest of the 23 state transmission utilities in the country. It is responsible for power transmission across the state at the 400 kV, 220 kV, 132 kV and 66 kV Voltage levels. The company also manages the state load dispatch centre, which monitors and controls the grid operations.

The Subhash Gram 220 KV Substation under West Bengal State Electricity Transmission Company Limited (WBSETCL) is situated 3 KM away from Subhasgram Railway station. Its commissioning date is 18th August 2009. This Substation is stretched over 22.59 acres. This substation mainly gets power from the nearby 400 KV Substation of Power Grid Corporation of India Limited (PGCIL).

It receives power at 220 KV voltage level from the nearby 440 KV PGCIL Substation and feeds it to Lakshmikantapur1, Lakshmikantapur2, Kasba, and KLC 220 KV Substation. Then the 220 KV supply is stepped down to 132 KV and feeds to Kasba1, Kasba2, Joka and Sonarpur132 KV feeder. Then the 132 KV supply is stepped down to 33KV and feeds to Madarhat and Baruipur. After that, the 33 KV is stepped down to 0.4 KV and supplied for auxiliary station service.

The Substation is well equipped with modern devices. It has two 220/132KV 160 MVA Power transformers, two 132/33KV 31.5 MVA Power transformers, two 33/0.4KV 630 KVA Station Service transformers and two 33/0.4KV 100KVA Earthing cum Station Service transformers. And also it has many Current Transformers (CT), Potential Transformers (PT), Capacitor Voltage Transformers (CVT), Wave Trap, Lightning Arrester, Central Break Isolators, Pantograph Isolators and a lot of safety equipment.

Subhash Gram 220 KV substation

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Substation layout

Subhash Gram 220 KV sub-station has three switchyards based on the three different voltage voltage levels.

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220 KV BAYS

•220 KV PGCIL-1

•220 KV PGCIL-2

•220 KV Kasba

•220 KV KLC

•220 KV LakshmikantpurFeeder-1

•220 KV LakshmikantpurFeeder-2

•220 KV bus coupler

•220 KV transfer bus coupler

•220 KV side of 160 MVA 220/132/33 KV TRF-1

•220 KV side of 160 MVA 220/132/33 KV TRF-2

132 KV BAYS

•132 KV side of 160 MVA 220/132/33 KV TRF-1

•132 KV side of 160 MVA 220/132/33 KV TRF-2

•132 KV side of 31.5 MVA 132/33 KV TRF-3

•132 KV side of 31.5 MVA 132/33 KV TRF-4

•132 KV Joka feeder

•132 KV Kasbafeeder-1

•132 KV Kasbafeeder-2

•132 KV Sonarpurfeeder

•Transfer bus coupler

33 KV BAYS

•33 KV side of 31.5 MVA 132/33 KV TRF-3

•33 KV side of 31.5 MVA 132/33 KV TRF-4

•Transfer bus coupler

•33 KV feeder-1

•33 KV feeder-2

•33 KV feeder-3

•33 KV feeder-4

•33 KV feeder-5

•33 KV feeder-6

Every equipment in the substation are well earthed. There is a large sheet made of metal conductor net bedded under the ground connected with every earth conductors of substation equipment. It is further connected with a low resistance metal plate (earth plate) which is buried about 70 Ft. deep into the ground.

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Single line diagram of Subhash Gram 220 KV substation

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Operation

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Receive power

Step down

voltage

Send power

Power is received in the substation through 2 PGCIL (Power Grid Corporation of India Limited) feeders. The receiving end voltage is 220 KV.Before they come in contact with other equipment, the three phases has to pass through lightning arresters.

Lightning arresters are protecting devices. It protects the substation equipment from over voltage or surges in transmission lines.

The typical lightning arrester has a high-voltage terminal and a ground terminal. When a lightning surge (or switching surge, which is very similar) travels along the power line to the arrester, the current from the surge is diverted through the arrestor, in most cases to earth.

After passing through the lightning arrester, one of the 3 phases passes through CVT i.e. Common Voltage Transformers.

A capacitor voltage transformer (CVT) is a transformer used in power systems to step-down extra high voltage signals and provide low voltage signals either for measurement or to operate a protective relay. In its most basic form the device consists of three parts: two capacitors across which the voltage signal is split, an inductive element used to tune the device to the supply frequency and a transformer used to isolate and further step-down the voltage for the instrumentation or protective relay. The device has at least four terminals, a high-voltage terminal for connection to the high voltage signal, a ground terminal andLightning arrester

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at least one set of secondary terminals for connection to the instrumentation or protective relay. CVTs are typically single-phase devices used for measuring voltages in excess of one hundred kilovolts where the use of voltage transformers would be uneconomical. In practice the first capacitor, C1, is often replaced by a stack of capacitors connected in series. This results in a large voltage drop across the stack of capacitors that replaced the first capacitor and a comparatively small voltage drop across the second capacitor, C2, and hence the secondary terminals.

Capacitor Voltage Transformer

In Subhash Gram substation, the CVTs are connected with each blue phases of every R-Y-B lines.CVTs also help receivers to receive high frequency signals that are for communication purpose.The remaining high frequency signals in the feeders are filtered by wave traps.

Wave trap or line trap is basically a low pass filter circuit used in substations.

The function of this trap is to trap the unwanted waves (high frequency communication signals). It is connected to the main incoming feeder so that it can trap the waves which may be dangerous to the instruments here in the substation.After that, the feeder passes through current transformers.

Wave trap

Current transformers are basically step up transformers basically used to steps down the current from 1600 or 800 amps to 1 amp so that it can be measured using sensitive low rating devices.

The main use of this transformer isa. Distance Protectionb. Backup Protectionc. MeasurementThere are 2 types of current transformers in the substation. One is live tank and the other is dead tank. In the live tank transformer, the tank is directly connected with the feeder, while in the dead tank type, the tank is insulated from the feeder and connected to earth conductor.And according to turns ratio also, there are two types of CTs. One is of 1600:1 rating and the other is of 800:1 rating.After current transformers, the feeders ends at the isolators.

Isolators isolate the feeders from the main bus. The main difference between circuit breaker and isolator is that circuit breaker is that circuit breaker can make or break a circuit but isolator is to be used only when the circuit is already open. It cannot break a closed circuit.There are two different types of isolators used in the substation.a. Pantograph Isolator or Jumperb. Centre Break Isolator

ClosedOpen

Pantograph isolator

Current Transformer (live tank)

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All 3 buses i.e. main bus-1, main bus-2 and transfer bus are separated from each other by these isolators.It is to be remembered that, before operating the isolators, we should ensure that the circuit is open. If not, then we first have to break the circuit using circuit breakers then operate the isolators.

Circuit breakers are used to make or break the circuit in high voltage lines.

Circuit breakers are also used for protection purposes. Whenever they sense any dangerous over current, over voltage, earth leakage etc. faults, they break the circuit immediately. They can be operated remotely from the control room. The insulation used in the circuit breaker should be very high in terms to avoid breakdown of the medium. This is why the circuit breakers used in the Subhash Gram substation are gas insulated (SF6). They provide better reliability than oil

Open

Closed

Centre break isolator

There are 2 main bus and a transfer bus in the 220 KV side. Each main bus is designed to take the full load without any fault.

Bus bar with isolators

Centre break isolator

Although, for operational efficiency related issues, both bus bars are kept energised.

The isolators are generally operated with 3 phase induction motors that can be controlled either individually or in gang operation mode. They can also be operated remotely from the control room.

insulated CBs. The best insulation property can be provided by vacuum circuit breakers. But they are very expensive and also difficult to maintain.

The interrupting chamber has been designed in such a way as to increase the mechanical resistance of the working part and take advantage of the low wear rate of the contacts subjected to the arc in SF6. The working part is enclosed, providing insulation between the circuit - breaker input and output.

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After the bus bars are energised, the electrical power is carried from the bus bars to a combination of two 160 MVA 220/132/33 KV transformers connected in parallel with the bus bars. The transformers step down the voltage from 220 KV to 132 KV and 33 KV.

A transformer is a device that transfers electrical energy from one circuit to another through inductively coupled conductors—the transformer's coils. A varying current in the first or primary winding creates a varying magnetic flux in the transformer's core and thus a varying magnetic field through the secondary winding. This varying magnetic field induces a varying electromotive force (EMF), or "voltage", in the secondary winding. This effect is called inductive coupling.

160 MVA Transformer

The technique used in the design and construction of high voltage transformer varies from manufacturer. The active part of transformer consists of core & winding. Other parts are- tank & cover, conservator, cooling accessories, etc.

Core is a manufactured form lamination of Cold Rolled Grain Oriented Silicon Steel, which gives very low specific loss at operating flux, is always in the direction of grain oriented. The core clamping structure is designed such that it takes care of all the forces produced in the winding in the event of any short circuit.

Winding are made from paper insulated copper conductors which are transposed at regular intervals throughout the winding for ensuring equal flux linkage and current distribution

between stands. Interleaved or shielded. construction adopted for high voltage winding to ensure uniform distribution of impulse voltage insulating spacers in the winding are arranged such that oil is directed through the entire winding for ensuring proper cooling.

Tank and cover are manufactured by welding steel plates and are suitable for withstanding full vacuum and positive pressure test as per CBIP manual. for large capacity power transformers ,the tank will be of bell type construction .this is to avoid lifting of heavy core and winding ,which are requires very large capacity crane at site .the weight of upper tank will be much less in comparison with that of core & winding and can be lifted by using a small capacity crane.

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Conservator function is to maintain the required transformer oil level in the main tank and OLTC above transformer internal accessories, allowing oil expansion and construction during temperature changes with breather, for installation of buchholz relay and gas collection and MOLG installation.

The transformers are provided with various cooling systems.For ONAN/ONAF cooling, oil flows through the winding external cooler unit attached to the tank by thermo-symphonic effect.For AF/OD, AF/OF WF cooling, the oil is directed through the winding by oil pumps provided in the external cooler unit.External cooler unit/units consists of pressed steel sheet radiators mounted directly on the tank or separate cooler banks for air-cooled transformer and oil to water heat exchanges for water cooled transformers.

A Dehydrating Breather is used to dry the air that enters a transformer as the volume of oil decreases because of fall in temperature. They are to be replaced with a new one when the blue colour turns into pink.

Conservator with air cell

Flexible Separation is fitted inside the cylindrical conservator. Oil being outside the separator is in direct contact with atmosphere.

Each valve should be cleaned from inside with compressed air jet. All particles should be removed from tank side..

It pumps the oil into the tank.

Consider the case of furnace Transformer in which one flow indicator can be mounted on suitable member of oil circulating pipe of heat changer. It can be used on liquid circulating pipes in chemical process.

It indicates the oil level in the tank. It is mounted on the oil tank with nut bolts. Several indicators are mounted in series for high capacity tanks.

The temperature indicator is used as an oil temperature indicator or as winding temperature indicator for the protection of liquid immersed power transformer.

Exhaust type cooling fans used on Transformer are designed to operate outdoors in all weather conditions.

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The parallel operation of transformers is common in any industry. This mode of operation is frequently required. When operating two or more transformers in parallel, their satisfactory performance requires that they have:

1. The same voltage-ratio2. The same per-unit (or percentage) impedance3. The same polarity 4. The same phase-sequence and zero relative phase-displacement

Out of these conditions 3 and 4 are absolutely essential and condition 1 must be satisfied to a close degree. There is more latitude with condition 2, but the more nearly it is true, the better will be the load-division between the several transformers.

This loss occurs due to electrostatic stress reversals in the insulation. It is roughly proportional to developed high voltage and the type and thickness of insulation. It varies with frequency. It is negligibly small and is roughly constant. (Generally ignored in medium voltage transformers while computing efficiency).

A sizeable contribution to no-load losses comes from hysteresis losses. Hysteresis losses originate from the molecular magnetic domains in the core laminations, resisting being magnetized and demagnetized by the alternating magnetic field.

Each time the magnetising force produced by the primary of a transformer changes because of the applied ac voltage, the domains realign them inthe direction of the force. The energy to accomplish this realignment of the magnetic domains comes from the input power and is not transferred to the secondary winding. It is therefore a loss. Because various types of core materials have different magnetizing abilities, the selection of core material is an important factor in reducing core losses. Hysteresis is a part of core loss. This depends upon the area of the magnetising B-H loop and frequency.

The losses in a transformer are as under.

1. Dielectric Loss2. Hysteresis Losses in the Core3. Eddy current losses in the Core4. Resistive Losses in the winding conductors5. Increased resistive losses due to Eddy Current Losses in conductors. 6. For oil immersed transformers, extra eddy current losses in the tank structure.

The alternating flux induces an EMF in the bulk of the core proportional to flux density and frequency. The resulting circulating current depends inversely upon the resistivity of the material and directly upon the thickness of the core. The losses per unit mass of core material, thus vary with square of the flux density, frequency and thickness of the core laminations. By using a laminated core, (thin sheets of silicon steel instead of a solid core) the path of the eddy current is broken up without increasing the reluctance of the magnetic circuit. For reducing eddy losses, higher resistivity core material and thinner (Typical thickness of laminations is 0.35 mm) lamination of core are employed. This loss decreases very slightly with increase in temperature. This variation is very small and is neglected for all practical purposes. Eddy losses contribute to about 50% of the core losses.B-H curve (hysteresis loop)

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These represent the main component of the load dependent or the variable losses, designated as I2R or copper losses. They vary as square of the r.m.s current in the windings and directly with D.C. resistance of winding. The resistance in turn varies with the resistivity, the conductor dimensions; and the temperature. R = ρ(l/A)Where,R = Winding resistance, Ωρ = Resistivity in Ohms - mm2/m.l = Length of conductor in metresA = Area of cross section of the conductor, mm2 In addition, these losses vary with winding temperature and thus will vary with the extent of loading and method of cooling.

Conductors in transformer windings are subjected to alternating leakage fluxes created by winding currents. Leakage flux paths, which pass through the cross section of the conductor, induce voltages, which vary over the cross section. These varying linkages are due to self-linkage as also due to proximity of adjacent current carrying conductors. These induced voltages, create circulating currents within the conductor causing additional losses. These losses are varying as the square of the frequency. For an isolated conductor in space, the varying self-linkage over the section, leads to clustering of the current near the conductor periphery. This is known as Skin Effect. The same effect, with the addition of flux from surrounding conductors, (Proximity effect) leads to extra losses in thick conductors for transformer windings. These losses are termed as Eddy Current Losses in conductors. The Test Certificate mentions the load losses, which include these eddy losses in conductors at supply frequency (50 Hertz) as also the eddy losses in tank structure in general at the same frequency in the case of oil cooled transformers. For dry type transformers, tank losses are absent. The contribution of eddy losses including tank losses, over the basic copper losses for an equivalent D.C. current, can be estimated from the difference in measured load losses and expected copper losses at the test current at the test temperature. For normal designs it ranges from 5% to 15%. Detailed subdivision is available only from design data. It can be taken as 10% of load losses in the absence of specific design data. These extra losses vary with square of frequency and square of per unit harmonic current. The eddy losses in the tank structure are equivalent to the dissipation in a loaded secondary with leakage reactance. The variation is not as the square of frequency, and it is customary to take a value of 0.8 for the exponent. The Eddy losses in a thick conductor can be

reduced by decreasing the radial thickness bysectionalising the conductors (multi-stranded) and increasing the axial dimension. The sectionalised conductor has to be transposed to make it occupy all possible positions to equalise the e.m.fs to the extent possible.It is important to transpose each layer so that each layer is connected in series with a path in each one of the possible N positions before being paralleled. Thus circulating current is forced to flow in a relatively very thin conductor..

Some leakage flux invariably goes in air paths away from the transformer. Strength of this stray flux diminishes and varies inversely with distance. If it links with any conducting material, it will produce eddy losses in that material. For oil immersed transformers, some stray flux links with some parts of the tank and causes extra eddy current losses in the structure. These losses are absent in dry type transformers. Similarly, extra flux due to outgoing L.T. conductors carrying large currents cause extra eddy current losses in the structural portion surrounding the leads. Both these losses vary with frequency 0.8 , as stated earlier.

The above discussion on transformer losses is given only to gain familiarity with the fundamental principles. The most important losses are core loss and copper loss. The other losses are described mainly to give a complete picture on losses.

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160 MVA transformer ratings

Type of on load tap changer

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31.5 MVA transformer ratings

Type of on load tap changer

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Communication

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In Subhash Gram substation, phase to phase double channel circuit is used to have a backup option. If by accident, one channel is broken, communication can still be done through the other channel.

After the signals are received by LMDU and LMU, they are sent to the PLCC room through underground or surface cables.

LMDU LMU

PLCC room

Wave trap Wave trap

CVT CVT

Line Matching Double Unit

Line Matching Unit

Phase to phase double channel system

Phase Phase

After the voltage is stepped down, the energy is carried to the 132 KV and 33 KV bus bars through feeders. Out going arrangement of the substation is the same but reversed as the incoming arrangement. The outgoing power has to pass all the various stages, that it had to face while incoming, but in reversed sequence.

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In Subhasgram Substation, the communication system is very good. There is a walkie talkie of very high frequency (VHF), which works with the help of a 12V DC charger. This walkie talkie is use to contact with Madarhat, Sonarpur and other nearby Substations. And also it is used to contact with yard with control room and to give the information to the control room about any fault observed at line patrolling time. The frequency of this Substation is 157.125. Wherever there is a machine of this frequency, it can contact with this Substation.There is another machine called PLCC (Power Line Career Communication). This machine is used to contact with the feeders. The carriers to the power line connection have been taken from co-axial cable. This PLCC is a combination of four lines.EPAX is a direct communication line between Subhash Gram 220 Substation, PGCIL, and the other three lines, KASBA, LAKHSMIKANTAPUR and KLC. These three lines operate through dialling via EPAX (Electronics Private Automatic Exchange) carrier through power line (works directly or through charger at 48 Volt DC). And, besides those there is a telephone, which is used for emergency contacts.Inside EPAX device

Each nearby substation has their unique frequency levels at which communication for different purposes are done.

Tx 195.57 KHz

Rx 191.57 KHz

Tx 207.57 KHz

Rx 203.57 KHz

Ch.1 Tx 223.57 KHz

Rx 215.57 KHz

Ch.2 Tx 227.57 KHz

Rx 219.57 KHz

Tx 143.57 KHz

Rx 147.57 KHz

Tx 135.57 KHz

Rx 139.57 KHz

Ch.1 Tx 151.57 KHz

Rx 159.57 KHz

Ch.2 Tx 155.57 KHz

Rx 163.57 KHz

Tx 183.57 KHz

Rx 187.57 KHz

Tx 107.57 KHz

Rx 111.57 KHz

Ch.1 Tx 119.57 KHz

Rx 127.57 KHz

Ch.2 Tx 123.57 KHz

Rx 131.57 KHz

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Conclusion

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Though the period of 19th January to 31st January (except holidays) was not enough to learn everything in

the substation, still I believe that, the knowledge & inspiration I gained and things I learned in the guidance of highly skilled professionals in Subhash Gram 220 KV

substation will help me becoming a dedicated and skilled electrical engineer in future.

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Subhash gram 220 KV substation is an ideal substation equipped with all modern machines and equipments. They are observed, tested and maintained in a regular basis. Safety is given a huge importance in the substation. There are fire fighting tools in every floor of the office and also all around the switchyard. There are safety and precaution related attractive posters stuck on the walls inside the office and control room. The switchyard and premises are nicely cleaned. The security personnel are very nice and friendly. The divisional and assistant engineers, working in the substation are highly talented professionals and also nice as a person. They helped us learning and understanding how things work in details and also cleared all of our doubts one by one with great interest and motivated us to try our best to become successful engineers.

Flowers of the garden of Subhash Gram 220 KV substation