Thursday, 9 January 2020

Basic Transmission of Electrical Energy

Basic Transmission


  • The process by which large amount of power produced are transported over a long distance for eventual use by costumer.
  • Large amount of power is generated at generating station. And the power stations are located away from the populated areas where fuel water is available. This has shifted power station quite away from costumers and it has to supply to customer.
  • The convince of electric power from a power station to costumer premises is called electric supply system.

This network is divided into two parts-
  1. Transmission 
  2. Distribution
Single line diagram of Transmission and Distribution of electric supply

Transmission and Distribution of Electric Power
Transmission and Distribution of Electric Power

Generating Station:

  • Electric energy is generated by 3-ph alternator. 
  • The generation voltage is 11Kv or 6.6 Kv. 
  • This voltage is to low to transmission over ling distance therefore it is step-up 132Kv/220Kv/400Kv by using step-up transformer.

Primary Transmission:

  • The voltage which step-up transformer is transmitted to bulk power stations with is called receiving stations.
  • Generally the power transmission of primary is carried out by 132Kv/220Kv/400Kv by 3-ph  3 wire system with overhead system to the outer side of city. This form  primary Transmission.

Secondary Transmission:

  • The primary transmission terminated at a receiving station which usually lies at outside of the city.
  • At the receiving station the voltage is reduce to 33Kv or 66Kv by step-down transformer. 
  • This voltage is transmitted at 33Kv or 66kv by 3-Ph, 3 wire ovrhead system to various substation located at in the city.this form secondary transmission.

Primary Distribution:

  • A secondary transmission line terminate at the substation where voltage is reduced from 33Kv/11Kv.
  • Large industrial consumers are supply at primary distribution level of 33Kv while smaller industrial consumers are supply at 11Kv and further handling with there own substation.

Secondary Distribution:

  • The electric power from primary distribution line i.e 11Kv is deliver to distribution substation.
  • These substation are located near the consumer localities and step-down the voltage to 400v, 3Ph, 4 wire for secondary distribution.
  • The voltage between any 2 phase is 400v and any phase and neutral is 230v.
  • The single phase residential lighting load is connected between any phase and neutral where as 3 ph, 400v motor load is connected to 3 ph supply.

Classification of transmission Line 

1)According to voltage level
  • Primary Transmission 
  • Secondary Transmission
2)According to length of Transmission line 
  • Short Transmission 
  • Medium Transmission
  • Long Transmission
3)According to type of supply
  • AC Transmission
  • DC Transmission
4)According to method of construction 
  • Overhead Transmission
  • Underground Transmission

1) According to voltage level

The transmission line are classified according to two types
  • Primary transmission- is 132Kv/220Kv/400Kv . The power in bulk amount is from generation station is transmitted to step-up transformer.
  • Secondary transmission- is 66Kv/ 33Kv. The power from step-up transformer is transmitted to step-down transformer. Voltage is reduced to 33kv or 66Kv  by step down transformer.

2) According to length of transmission line

  • Short Transmission Line- When length of overhead transmission system is upto 50km and line voltage is lower than 20kv is called short transmission line.
  • Medium Transmission Line- When length of overhead transmission system is about 50km to 150km and line voltage is about 20Kv to 100Kv it is called medium transmission line.
  • Long Transmission Line- When the length of transmission system is more than 150km and voltage is more than 100kv it is called long transmission line.

3) According to method of construction

  • Overhead Transmission Line- In this method power is transmitted by overhead conductors. this overhead conductors are suspended freely in atoms by using supporting tower, insulator etc
  • Underground Transmission Line- In This method power is transmitted by underground cable consist of conductor at the center and surrounding tower, insulator etc.


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