Synchronous Generator MCQs Part 10

Contents

- 1 An alternator is sometimes also called as
- 2 In order to generate 50 cycles per second the speed at which a 6-pole alternator should be driven is
- 3 A 3 phase synchronous generator generates an open circuit phase voltage of 2000 V when the exciting current is 50 A
- 4 The frequency of system to whom several alternators are paralleled can be increased by simultaneously
- 5 Majority of the alternators are

## An alternator is sometimes also called as

An alternator is sometimes also called as:

- Asynchronous generator
- Synchronous generator
- Rosenberg generator
- 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:

- 500 RPM
- 1000 RPM
- 1500 RPM
- 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:

- 2.5 Ω
- 5 Ω
- 7.5 Ω
- 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:

- Increasing the speed of prime movers of all generators
- Decreasing the speed of prime movers of all generators
- Increasing the field excitation of all generators
- 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:

- Single phase
- Two phase
- Three phase
- None of the above

Correct answer: 3. Three phase