Electric supply is required for power plants for various reasons.
We all know 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 how these power plants will get the supply. In fact, power plants need both AC and DC supplies. Now there is another question that arises here, why do they need DC supply? To know the answer read the rest of the article without skipping.
A reliable source of electric supply is mostly needed for operating power plants. So redundancy is always considered to get reliable supply.
Electric Supply Systems in Power Plants:
The various types of Electric supplies required in a power plant are
- Sation Supply
- Unit supply
- D.C Supply
- Emergency Supply
1. Power Plants Station Electric 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 any unit and in case of emergencies.
- 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 the grid.
2. Power Plants Unit Electric 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 use station supply so all the equipment which are running using station supply is now changed to using Unit supply. This is the critical operation done in the power plants using Bus-Transfer. The complete details of the bus transfer are explained here.
- 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 the unit bus.
3. Power Plants D.C Electric Supply:
DC Supply is the heart of any protection system. 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 set up by the battery banks in the power plant itself.
- FCBC Chargers:
In the case of DC supply, AC is taken from the station bus and rectified to obtain DC using FCBC Chargers. In case even power from the grid is not available, then the battery bank can provide DC power.
4. Power Plants Emergency Electric Supply:
In power plants, some auxiliaries should not stop for the specified time without any interruption. What if a complete blackout occurs and DC backup also runs out after some time. In this case, all the essentially run auxiliaries will get supplies from an Emergency source.
- Diesel Generator:
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.
Voltage Levels in Power Plants:
Normally Supply is A.C with these voltages:
[These are taken as example voltages only].
A.c supply voltages:
1. 11KV.
2. 6.6KV.
3. 415V.
D.C supply voltages:
- 220V for Emergency
- ±24V for Instrumentation and control
