Synchronous motors are AC electrical machines that convert electrical power to mechanical power. The working principle of synchronous motors is based on the interaction of the magnetic field of the stator in combination with the magnetic field of the rotor. In stator, 3-phase windings are included and are operated on the 3-phase current. The stator winding generates a three-phase rotating magnetic field. A DC current is provided to the rotor circuit. Synchronous motors are practically employed in applications where constant and precise speed operation is required. MCQs.net shares the top 10 MCQs on Synchronous Motors:

## The three-phase synchronous motor has

The three-phase synchronous motor has:

- One slip-ring
- Two slip-rings
- Three slip-rings
- Four slip-rings

Correct answer: 2. Two slip-rings

## A synchronous motor can be employed as a synchronous capacitor for the condition when it is

A synchronous motor can be employed as a synchronous capacitor for the condition when it is:

- Under-excited
- Over-excited
- Under-loaded
- Over-loaded

Correct answer: 2. Over-excited

## Synchronous motor runs at speed that is

Synchronous motor runs at speed that is:

- Higher than synchronous speed
- Lower than synchronous speed
- Same as synchronous speed
- None of these

Correct answer: 3. Same as synchronous speed

## Back EMF of synchronous motor depends on

Back EMF of synchronous motor depends on:

- Load
- Speed
- Load angle
- None of these

Correct answer: 3. Load angle

## Percentage slip in case of synchronous motors is

Percentage slip in case of synchronous motors is:

- Zero
- 0.5%
- 1%
- 99.98%

Correct answer: 1. Zero

## For load increase, a synchronous motor running with normal excitation adjusts itself by

For load increase, a synchronous motor running with normal excitation adjusts itself by:

- Increasing armature current
- Increasing back EMF
- Increasing power factor
- Increasing torque angle

Correct answer: 1. Increasing armature current

## The slip rings in synchronous motor carry

The slip rings in synchronous motor carry:

- AC current
- DC current
- Both of these
- None of these

Correct answer: 1. DC current

## The speed of synchronous motor

The speed of synchronous motor:

- Increases with increases in load
- Increases with decreases in load
- Always remains constant
- None of these

Correct answer: 3. Always remains constant

## Damper windings in synchronous motor are provided on

Damper windings in synchronous motor are provided on:

- Pole faces
- Rotor shaft
- Stator frame
- None of these

Correct answer: 1. Pole faces

## If field of the synchronous motor is under excitement the power factor will be

If field of the synchronous motor is under excitement the power factor will be:

- Unity
- Zero
- Leading
- Lagging

Correct answer: 4. Lagging

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