# Synchronous Motor MCQs Part 1 with Explanatory Answer

Filed Under: Synchronous Motor MCQs

## Speed regulation of synchronous motor is

Speed regulation of synchronous motor is:

1. 0
2. 5
3. 89
4. 100

Explanation: Speed regulation of machine is defined as the ratio:

SR = {S (NL) – S (FL)} / S(FL)

where S (NL) = Speed of motor at no load

S (FL) = Speed of motor at full load.

The speed synchronous motor remains constant from no load to full load thus the

## An over-excited synchronous motor

An over-excited synchronous motor:

1. Takes reactive power
2. Supplies reactive power
3. Neither takes nor supplies
4. Any of above

Correct answer: 2. Supplies reactive power

Explanation: Such motor draws current at leading PF and behaves as large capacitor. It can be used for power factor correction equipment.

Synchronous motors are started by

Synchronous motors are started by:

1. Using external prime mover
2. Using Amortisseur windings
3. Reducing speed of stators magnetic field
4. All of above

Correct answer: 4. All of above

## If one of 3-phases is short-circuited, the induction motor will

If one of 3-phases is short-circuited, the induction motor will:

1. Not start
2. Overheat
3. Continue to work as it did previously
4. None of above

## Hunting in synchronous motor happens due to

Hunting in synchronous motor happens due to:

2. Change in excitation
3. Change in frequency of the supply
4. Any of above
5. None of above

Correct answer: 4. Any of above

## The operating speed of the synchronous motor can be changed by

The operating speed of the synchronous motor can be changed by:

1. Changing supply frequency
3. Changing voltage
4. Changing excitation method

Correct answer: 1. Changing supply frequency

## The load on synchronous motor running with fixed excitation in doubled, the torque angle becomes

The load on synchronous motor running with fixed excitation in doubled, the torque angle becomes:

1. Halved
2. Remains constant
3. Doubled
4. 7.99 of original

## Stability and excitation of synchronous motors are

Stability and excitation of synchronous motors are:

1. Directly related
2. Inversely related
3. Exponentially related
4. Not related

## For same parameters the PF of the synchronous motor is

For same parameters the PF of the synchronous motor is:

1. Better than induction
2. Worst than induction
3. Identical to induction
4. Any of above

Correct answer: 1. Better than an induction motor

Explanation: The stator supply of synchronous motor is relieved from producing a magnetic field

## Maximum power is developed at a load angle of

Maximum power is developed at a load angle of:

1. 45º
2. 60º
3. 75º
4. 90º