Electric Supply Systems in Power Plants

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Electric Supply Systems in Power Plants:

We all know that how can we get the electric supply for our homes using the distribution network provided by the electric companies. As we know power plants are the main source of supply and they are located far away from our homes.

In this scenario it is interesting to know that how these power plants will get the supply. In fact power plants need both AC and DC supplies. Now there is another question arises here, why they need DC supply?  To know the answer read the rest of the article without skipping.

Reliable source of electric supply is mostly needed for operating power plants. So redundancy is always considered to get reliable supply.

The various types of supplies required in a power plant are

1. Use of Station Supply:

Station supply is given to all the plants (Coal Handling plant, Ash Handling Plant, etc.) which are common to all the individual units.

It also provides supply at the time of starting to any unit and in case of emergencies.

2. Use of Unit Supply:

When the unit starts generating the unit supply starts giving supply to its unit auxiliaries. Once the unit starts generating there is no need to using station supply so all the equipment which are running using station supply are now changed to using Unit supply. This is the critical operation doing in the power plants using Bus-Transfer. The complete details of bus transfer explained here.

3. Use of D.C Supply:

D.C supply is used in case of emergencies and for some Instrumentation control circuits. The major control circuit in Electric Switchgear is mainly operated using DC supply as it is reliable and easily setup by the battery banks in the power plant itself.

DC battery bank providing DC supply to Power plant
DC Battery Bank at Power Plant

4. Use of Emergency Supply:

In power plants some auxiliaries should not stop for the specified time without any interruption. What if complete blackout occurs and DC back up also runs out after some time. In this case all the essentially run auxiliaries will get supply from Emergency source.

  • The various voltage levels required are

Normally Supply is A.C with these voltages:

[These are taken as example voltages only].

1. 11KV.

2. 6.6KV.

3. 415V.

D.C supply voltages:

  1. 220V for Emergency
  2. ±24V for Instrumentation and control
  • How to get this supply?

The various supplies mentioned above are obtained from the following ways.

1. Station Transformer:

Station transformer provides station supply. It is a power transformer which takes power from the grid and steps down the voltage and gives supply to the plants which are common to all the units through a station bus of 6.6KV.

Here Grid is a reservoir. It is an interconnection of numerous power plants. The power plant owners need to pay for consuming power from grid.

2. Unit Auxiliary Transformer:

The power plant cannot always take power from the grid as it is not economical. Hence, a part of the power generated is utilized by the unit auxiliaries. This is done by Unit Auxiliary Transformer.

This transformer steps down the generated voltage and gives supply to the unit auxiliaries through unit bus.

3. D.C Supply:

In case of DC supply, AC is taken from station bus and rectified to obtain DC using FCBC Chargers. In case even power from grid is not available, then battery bank can provide DC power.

4. Emergency Supply:

The emergency supply is provided by using Diesel Generator. This will start automatically in case the supply fails. Special control circuits like hold on coils are used so that all the equipment gets the uninterrupted supply.

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