Single Line Diagram of a Transmission Distribution in a Power System

Single Line Diagram One Line Diagram

What is a Single Line Diagram?

A Single Line Diagram or a One Line Diagram is a simple way to draw the Electrical Circuit in a Power System. By adopting this Electrical Line Diagram the Complexity of the Pictorial Representation can be reduced.

A typical Electrical Single Line Diagram Consist of a

  • Generator (Generating Station)
  • Step Up Transformer
  • Step Down Transformer
  • Sub-Station
  • Feeder
  • Distributors

Primary Transmission:

  • The Power Generated from the Generating Station is step Up using the Step-Up Transformer and then the Primary Transmission Takes Place.
  • Step-Up Transformer is used to Minimise the Transmission Loss.
  • 11Kv is Step Up to 220Kv before sending to Primary Transmission.
  • In other Words, Primary Transmission is also called High Voltage Transmission since it deals with very high Voltage.
  • Primary Transmission uses 3 phase 3 Wire System (Over Head Transmission Lines)

Secondary Transmission: 

  • At the Receiving Station, the voltage level is step-down from 220Kv to 33KV using Step-Down Transformer.
  • Second Transmission System uses 3 phase system to Transmit Power to the various Sub-stations.

Primary Distribution:

  • In the Primary Distribution, a step-Down transformer (Usually called as Distribution Transformer) is used to reduce the Voltage to the desired Level.
  • The Voltage is Step down from 33KV or 22Kv to 6.6Kv or 3.3Kv.
  • Large Factories and Industries get power from Primary Distribution. Companies using Primary Distribution have their own Sub-station.
  • It is also called High-Voltage Distribution.

Secondary Distribution: 

  • In Secondary Distribution, a Step-down transformer is again used to reduce the voltage level from 3.3 Kv to 440V or 230v.
  • The End consumers get power through Secondary Distribution.
  • 230V is used for Domestic Purposes.
  • It is also called Low Voltage Distribution.
  • The Secondary Distribution uses 3 phases and 4 wire system (Neutral Wire)










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