Power Systems
To prevent maloperation of deferentially connected relay while energizing a transformer, the relay restraining coil is biased with

  5th harmonic current.
 2nd harmonic current.
 7th harmonic current.
 3rd harmonic current.

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Power Systems
Gross head of an hydroelectric power station is

 the height of water level in the river where the tail race is provided.
 the height of water level in the river where the storage is provided.
 all of above.
  the difference of water level between the level in storage and tail race.

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