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Overspeed protection of the alternator is done with the help of
1. Over current relay
2. Alarm
3. Governor
4. Differential relay

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Correct Answer - Option 3 : Governor

Over-speed protection:

  • Over-speed protection must be selective and must not shut the unit down due to a temporary loss of load, even if the cause is serious i.e. short circuit.
  • Short circuits anywhere near a generator will collapse the voltage and the generator experiences a loss of load.
  • While it is the general practice to provide mechanical over speed devices on both steam and hydro turbine, which operate directly on the steam throttle valve or main step valve, it is not usual to backup this devises by an over speed relay on steam driven sets.
  • On hydroelectric units, as the response of the governor is comparatively slow and the set is more prone to over-speed. The relay when fitted is usually supplied from the permanent magnet generator used for the control of governor.

 

Differential relay:

  • Differential relay operation depends on the phase difference of two or more electrical quantities.
  • It works on the principle of comparison between the phase angle and the magnitude of the same electrical quantities.
  • The differential relay is used for the protection of the feeder, large busbars, etc.

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