Circuit Breaker and Earthing Switch of AC locomotive

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Circuit Breaker and Earthing Switch
Question
Q. Explain the purpose of equipment’s in AC locomotive breaker and earthing switch.

Answer

  • Circuit breakers are the main electrical components use for the protection of the track power circuit from any type of faults.
  • The circuit breakers used in the traction Power circuit are of various types. It depends on their location.
  • They are classified as High voltage breakers, 25kV circuit breakers, feeder circuit breaker etc.
  • The circuit breakers used in the traction power circuits are mostly of Air blast type and Vacuum type circuit breakers.
  • Air Blast Circuit Breakers are designed for the isolation of power to the traction motor in the event of faults.
  • Air Blast Circuit Breaker needs greater amount of maintenance due to inbuilt features like large number of parts (approximately 735 parts), complex control block and extinguishing of arc during breaking of current in the air.
  • Due to this the life of main contact is too limited. This breaker also requires large amount of dry air for each switching operation. Some of these disadvantages are overcome in vacuum type circuit breakers.
  • Vacuum Type circuit breaker is having simplified design and with lesser number of parts (Approximately 260 parts).
  • Also it has simplified control block and self containing interruption medium i.e. vacuum.
  • Due to the above features the life of the main contacts is more as compared to Air blast circuit breaker.
  • Along with this, it also offers the advantages of reduced size, reduced weight and reduced maintenance cost as compared to these for air blast circuit breakers.
  • They are used for higher rating as compared to air blast circuit breakers.
  • The function of both the circuit breaker is same i.e. to interrupt the power in case of faults.
  • Earthing switch is provided to every traction power circuit. The earthing switch is to be closed whenever the line maintenance is to be done on the system.
  • For the operation and maintenance of the lines, the circuit breakers are opened first and then the earthing switch is closed. If by any reason the charge still present on the line will get discharge through ground with the help of earthing switch.
  • It provides an additional protection to the person who is performing maintenance on the line.

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