WBSETCL Subhash Gram 220KV Substation Training Report
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WBSETCL SUBHASH GRAM 220 KV SUB-STATION
SUBMITTED BY- ARIJIT BASU
EE, DIPLOMA, 3RD
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
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
Subhash Gram 220 KV sub-station has three switchyards based on the three different voltage voltage levels.
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.
Single line diagram of Subhash Gram 220 KV substation
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
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.
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
Current Transformer (live tank)
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
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.