Synchronous Generator MCQs Part 10

Synchronous Generator MCQs Part 10

An alternator is sometimes also called as

An alternator is sometimes also called as:

1. Asynchronous generator
2. Synchronous generator
3. Rosenberg generator
4. None of the above

Correct answer: 2. Synchronous generator

In order to generate 50 cycles per second the speed at which a 6-pole alternator should be driven is

In order to generate 50 cycles per second the speed at which a 6-pole alternator should be driven is:

1. 500 RPM
2. 1000 RPM
3. 1500 RPM
4. none of these

Correct answer: 2. 1000 RPM

Explanation: N = 120f/P = 120*50/6 = 1000 RPM

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

The frequency of system to whom several alternators are paralleled can be increased by simultaneously

The frequency of system to whom several alternators are paralleled can be increased by simultaneously:

1. Increasing the speed of prime movers of all generators
2. Decreasing the speed of prime movers of all generators
3. Increasing the field excitation of all generators
4. Decreasing the field excitation of all generators

Correct answer: 1. Increasing the speed of prime movers of all generators

Majority of the alternators are

Majority of the alternators are:

1. Single phase
2. Two phase
3. Three phase
4. None of the above

Correct answer: 3. Three phase