Synchronous Motor MCQs Part 1 with Explanatory Answer

Filed Under: Synchronous Motor MCQs

1. Speed regulation of synchronous motor is:

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

Correct answer: 1. 0

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

2. 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.

3. 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

4. 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

Correct answer: 2. Overheat

5. Hunting in synchronous motor happens due to:

1. Change in load
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

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

1. Changing supply frequency
2. Changing connected load
3. Changing voltage
4. Changing excitation method

Correct answer: 1. Changing supply frequency

7. 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

Correct answer: 3. Doubled

8. Stability and excitation of synchronous motors are:

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

Correct answer: 4. Not related

9. 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

10. Maximum power is developed at a load angle of:

1. 45º
2. 60º
3. 75º
4. 90º

Correct answer: 4. 90º

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