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Induction Motor Interview Questions with Answers | Part-1

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Selection of voltage for high voltage transmission lines

Selection of voltage for high voltage transmission lines

As power plants are located for away from the load centers so it is necessary transmit power at high voltages.

Selection of voltage
Selection of voltage for high voltage Transmission Line


Selection of voltage level depends on the following factors:
  1. Conductor size
  2. Future load growth
  3. Grid inter connection
  4. Cost of the transmission line
  5. Cost of equipment e.g. transformers insulators insulators, circuit breakers etc.
  6. Transmission line length
  7. Voltage regulation
  8. Power loss
  9. Intial and operating cost
There is a exponential increase in the cost for voltage level above 220 kV and above.

Voltages in India are:
  • For short transmission line - 11kV, 22kV and 33 kV
  • For medium transmission line - 66kV
  • For long transmission line - 110kV, 220kV, and 440kV
Future load growth depends on the possible development in that region.

The choice of voltage level also depends on the conductor size. Conductor size affects the performance of transmission line in the form of transmission loss and voltage regulation.

Cost of the transmission line depends on the conductor material chosen. Conductor material selected should have lower value of resistance.

If chosen voltage level is large than equipment used should have larger ratings. Cist of equipment increases with the increase in the ratings of the equipments.

General transmission voltage is given as :
General transmission voltage formula
General transmission voltage formula

Where,
  • E - Transmission Voltage (kV) (line - line)
  • L - Distance of transmission line
  • KVA - Power need to transfer

To ensure reliable and economical power supply, all electrical power system networks of grids are need to be interconnected. So interconnection grid voltage need to be fixed. 

If it is variable it results into synchronisation problem which ultimately increase the cost of power system networks.

Spacing between conductors depends on the voltage level of transmission line. If transmission line voltage is larger than spacing between conductors need to be taken larger to avoid over lapping magnetic interfaces of each transmission line conductors.

Below table indicates the general minimum and maximum length of transmission line in km for line to line voltage (kV).
General minimum and maximum length of transmission line
General minimum and maximum length of transmission line


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Comments

  1. AbbasOctober 5, 2021 at 9:32 AM

    Thank you for this information, can you add how to select or determine the size of high Voltage transformers.

    ReplyDelete

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