Synchronous Generator MCQs Part 7

Synchronous Generator MCQs Part 7

The stator of an alternator is identical to which of following machines

The stator of an alternator is identical to which of following machines:

  1. DC Generator
  2. 1-phase induction motor
  3. 3-phase induction motor
  4. Rosenberg generator

Correct answer: 3. 3-phase induction motor

With the size of the machine, the full-load efficiency of alternator

With the size of the machine, the full-load efficiency of alternator:

  1. Increases
  2. Decreases
  3. Remains constant
  4. None of these

Correct answer: 1. Increases

Effect of cross magnetization in synchronous generator makes it voltage

Effect of cross magnetization in synchronous generator makes it voltage:

  1. Non-sinusoidal
  2. Truly sinusoidal
  3. Free from harmonics
  4. None of these

Correct answer: 1. Non-sinusoidal

In an alternator, the armature reaction influences which of following

In an alternator, the armature reaction influences which of following:

  1. Windage losses
  2. Operating speed
  3. Generated voltage/phase
  4. None of the above

Correct answer: 3. Generated voltage/phase

A 3 phase synchronous generator generates an open circuit phase voltage of 2000 V when the exciting current is 50 A

A 3 phase synchronous generator generates an open circuit phase voltage of 2000 V when the exciting current is 50 A. The short circuit current for same excitation being 400 A. The value of synchronous reactance per phase is:

  1. 2.5 Ω
  2. 5 Ω
  3. 7.5 Ω
  4. 12.5 Ω

Correct answer: 2. 5 Ω

Explanation:

Synchronous reactance (Xs) = Eph/Isc = 2000/400 = 5 Ω

Where in the formula

Eph = Rated open circuit phase voltage

Isc = Short circuit current per phase using same exciting current that was required to produce Eph

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