Butibori Substation

Located at a distance of 30km from Nagpur (main city), Butibori is one of the many substations in Nagpur. This 220kV substation has twenty four 33kV feeder, four 132kv feeders and fourteen 220kV feeder of which 2 belongs to VIPL category.

Before going further let me first clear why do we require a substation?
The main purpose the substation is to make the power generated at the power plant available to the people. The high voltage in which they transmit the power can’t be directly put to use. These need to be stepped down to convenient level before it is send to the customers. Here comes the role of substation. The substation steps down the voltage according to the requirement of the utility.
The other term which may trouble you a bit is Feeder. What do we mean by feeder?
In simple terms, all the connection which draw and give power to the grid are called feeder.

Components of power plant substation:

1.    Transformer
2.    Bus bars
3.    Circuit Breakers
4.    Current Transformers(for auxiliary)
5.    Potential Transformers(for auxiliary)
6.    Isolators
7.    Lightening Arresters
8.    Insulators
9.    Overhead Ground Wire
10.    Control Room Containing various auxiliaries
11.    DC Battery

Transformer:

 

 
Butibori has three 500MVA 3phase power transformer of 220kv/33kv. These transformers are provided with ONAN and ONAF cooling mechanism. Tapings are provided to alter the voltage available to the utilities in case they complain against less terminal voltage appearing at their end. Complete detail of the transformer is as under:

Accessories of transformers:

1.    Buchholz relay
2.    Conservator
3.    Silica jell breather

Action of Buchholz Relay:

Buchholz relay is a mechanical actuator, which trips the transformer in case of internal faults like insulation breakdown, short circuit of winding etc. Due to these faults the temperature rises and there is decomposition of insulating oil and gases are produced which get accumulated in the upper part of the Buchholz relay. This leads to tilting of the mercury switch. Based upon the level, the alarm is produced and relay comes in action.
The operator in control room receives an alarm, the transformer is turned off. The mouth of the gas valve on Buchholz relay is opened and a match is lighted. If the gas escaping the transformer catches fire, then this is an indication that the winding have burned and it requires immediate maintenance. On the other hand if it does not catch fire, then it is an indication that air was collected. The air is allowed to escape and the normal function of the transformer is resumed.

Conservator

 

Now it happens that the oil which is circulated through the transformer for cooling may expand or contrac
t depending upon the varying temperature and pressure condition to which it is exposed. In summer there is an expansion of the oil. If suitable arrangement is not made for the storage of excess oil, then the oil tube may bust. On the other hand, in winter season, due to contraction, the availability of oil necessary for cooling the transformer will be less leading to shortening of the life of transformer. Here comes the action of conservator. The conservator stores the oil in case of expansion and provides the deficit amount in winter.

 Silica Jell

 

One of the biggest enemy of transformer is the moisture. To deal with these, the transformer are provided with silica jell box. It is blue in colour. As it absorbs moisture it becomes pinkish. Then it is required to be replaced. They can be reused after placing them in light for some time. They lose their moisture content and become blue again and ready to be reused.

Bus Bars:

 

The bus bars are aluminium or copper conductors which carry electric current in open air to which various connection (feeders, equipment) can be made. There arrangements are such that work on any equipment can be done without causing any trouble to incoming and outgoing feeders.
The 220kV butiburi substation has Double bus bar with auxiliary bus arrangement. It has two main and 1 auxiliary line. This ensures that the supply is not affected if one line goes faulty.

Circuit Breakers:

 

Circuit Breakers used for making and breaking of electrical contacts. This task can’t be done in open air as this high voltage will ionize the air and produce spark. Circuit breaker contains inert medium in which the making and breaking of contact is done. Their outer cover is made of porcelain. Also they ensure that the operation is done very fast so that arc is quenched faster. In butibori, the circuit breaker are inert gas type which contain SF6. Before the circuit breaker is operated, it is necessary to ensure that correct pressure is maintained in the circuit breaker and the gas cylinder.

Isolators:

 

Isolators are disconnection switch. They can be controlled from switch yard or from the control room. These isolators are in open air, so they are used only in no load condition ie. they are operated only after the circuit breaker is brought to action. By looking at the position of the isolators we can tell whether it is connected or disconnected.
Current Transformer and Potential Transformer:
For the safety of the instruments and economic reasons, we need to keep a record of the current and voltage at various points in the circuit. Such high voltage and current is highly unsafe to directly give to the measuring equipment. Their values have to be lowered down. For this we require CT and PT. These can be seen at various points in the switch yard. These are step down transformers. Both of them appears almost same but PT is a bit conical compared to cylindrical structure of CT. They have two input wires and two outgoing wires.

 

Current Transformer and Potential Transformer:

 

For the safety of the instruments and economic reasons, we need to keep a record of the current and voltage at various points in the circuit. Such high voltage and current is highly unsafe to directly give to the measuring equipment. Their values have to be lowered down. For this we require CT and PT. These can be seen at various points in the switch yard. These are step down transformers. Both of them appears almost same but CT is a bit conical compared to cylindrical structure of PT. They have two input wires and two outgoing wires.

Insulators:

 

The heavy current carrying conductors if directly mounted on the poles or support will directly ground them to earth. So we requires some insulator through which we can hang them on poles and propagate them. The insulators should have high resistivity to prevent the leakage of current to earth. Along with this it should be able to withstand the weight of the conductor (wire). Depending upon the rated kV the line is carrying the size of conductor changes so does the insulator required to support them. For 33kV and below we use pin type insulator and for higher rating we use suspension type insulators. These insulators have porcelain covering. These have discs whose number depend upon the kV rating of the line. Eg. If the discs are of 11kV rating, then we would require 20 of them to hang the conductor through the support. Butibori substation has suspension type insulators in switch yard.

Lightening Arrester:

 

One of the biggest thread to the Substation is Lightening. 100s of kV smashing on the equipment all of a sudden renders them useless. Lightening arrester protect the substation (most probably the switchyard) from the effect of lightening. These are connected between line and ground. They have a spark gap in between them which remains non-conducting as long as normal power is flowing through it. But when the lightning strikes, it becomes conducting and all power in the lightening goes to ground safely and the spark gap becomes non-conducting again.
Overhead ground wire:
These are steel wires which run over the top of each transmission line tower. These are solidly grounded at each tower. They also help to minimize the effect of lightening surges by grounding them safely.

 

Overhead Ground Wire

 

These are steel wires which run over the top of each transmission line tower. These are solidly grounded at each tower. They also help to minimize the effect of lightening surges by grounding them safely.

Control room:

It has arrangement for the remote monitoring of each of the auxiliaries, feeders etc. and controlling them. Various components in control room are as shown below:
Slides

DC  Battery:

 For the proper functioning of the relay and other protective gears we requires uninterrupted dc supply. They are crucial even when the whole grid terminates. Butibori substation has 110 cells of 2V each connected in series to provide 220V for the proper functioning of the auxiliaries.