If the alternator is over-excited and it delivers reactive power to the infinite bus, then under this condition:

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  1. the alternator is operating at unity power factor
  2. the alternator is operating both at leading and lagging power factor
  3. the alternator is operating at leading power factor
  4. the alternator is operating at lagging power factor

Answer (Detailed Solution Below)

Option 4 : the alternator is operating at lagging power factor
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Detailed Solution

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Excitation of Synchronous Generator (Alternator):

Leading power factor: If field excitation is such that Eb < V the generator is said to be under excited and it has a leading power factor. So that it absorved reactive power.

Lagging power factor: If field excitation is such that Eb > V the generator is said to be over-excited and it draw lagging current. So that it delivered reactive power.

Unity power factor: If field excitation is such that Eb = V the generator is said to be normally excited.

V -curve for synchronous generator is shown below

Mistake Points

For Synchronous Motor:

Over-excited Synchronous Motor works at the leading power factor

The normal excited Synchronous Motor works at the  lagging power factor

The Under excited Synchronous Motor works at lagging power factor

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