Synchronous Generator MCQ Part 7

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To produce an EMF at give frequency, the alternator will run at greatest speed for which number of poles

To produce an EMF at give frequency, the alternator will run at greatest speed for which number of poles:

  1. 2
  2. 8
  3. 12
  4. 16

Correct answer: 1. 2

Explanation: From formula

Speed = 120*f/P

Indicates that the lower the number of poles, the higher will be the speed. Simply saying the speed and pole number are inversely related to each other.

The D.C armature resistance of a Y connected alternator, when measured across the two terminals, comes out to be 0.4 ohms. The per-phase resistance is

The D.C armature resistance of a Y connected alternator, when measured across the two terminals, comes out to be 0.4 ohms. The per-phase resistance is:

  1. 0.1 ohms
  2. 0.2 ohms
  3. 0.4 ohms
  4. 0.8 ohms

Correct answer: 2. 0.2 ohms

Explanation:

The DC armature resistance of Y connected alternator measured across the two terminals is of two phases. The per-phase resistance is half of that value: 0.4/2 = 0.2 ohms

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