Electric Supply Systems in Power Plants :
Grid:
Grid is a reservoir. It is an interconnection of numerous power plants.
The various types of supplies required in a power plant are
- 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.
- Unit Supply:
When the unit starts generating the unit supply starts giving supply to its unit auxiliaries.
- D.C Supply:
D.C supply is used in case of emergencies and for some Instrumentation control circuits.
The various voltage levels required are
Normally Supply is A.C with these voltages:
1.11KV.
2.6.6KV.
3.415V.
D.C supply voltages:
- 220V for emergency
- ±24V for Instrumentation and control
How to get this supply?
The various supplies mentioned above are obtained from the following ways.
- 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.
- 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.
- D.C Supply:
In case of DC supply, AC is taken from station bus and rectified to obtain DC. In case even power from grid is not available, then batteries can provide DC power.