If the excitation of the synchronous generator fails, it acts as a/an

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SSC JE EE Previous Year Paper 14 (Held On: 26 Sep 2019 Morning)

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Answer 1

Normally the alternators are connected to the system to which a number of other alternators are also connected and hence the system behaves as an infinite bus.
Due to the influence of this in finite buses, there will be a rotating magnetic field in the stator windings of all alternators, and these fields are all rotated in synchronous speed.
The field created by the rotor windings gets locked with this rotating magnetic field of the stator and also rotates at the same speed.
If the excitation of the generator fails, suddenly there will be no more magnetically locking between the rotor and rotating magnetic field of the stator.
But still, the governor will supply the same mechanical power to the rotor due to this sudden magnetic unlocking; the rotor will be accelerated beyond the synchronous speed.
Hence there will be a negative slip between the rotor and rotating magnetic field which creates large slip frequency currents in the rotor circuit to maintain the power output of the machine as an induction generator.