Synchronous Motor MCQs Part 1 with Explanatory Answer
Filed Under: Synchronous Motor MCQs
1. Speed regulation of synchronous motor is:
- 0
- 5
- 89
- 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:
- Takes reactive power
- Supplies reactive power
- Neither takes nor supplies
- 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:
- Using external prime mover
- Using Amortisseur windings
- Reducing speed of stators magnetic field
- All of above
Correct answer: 4. All of above
4. If one of 3-phases is short-circuited, the induction motor will:
- Not start
- Overheat
- Continue to work as it did previously
- None of above
Correct answer: 2. Overheat
5. Hunting in synchronous motor happens due to:
- Change in load
- Change in excitation
- Change in frequency of the supply
- Any of above
- None of above
Correct answer: 4. Any of above
6. The operating speed of the synchronous motor can be changed by:
- Changing supply frequency
- Changing connected load
- Changing voltage
- 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:
- Halved
- Remains constant
- Doubled
- 7.99 of original
Correct answer: 3. Doubled
8. Stability and excitation of synchronous motors are:
- Directly related
- Inversely related
- Exponentially related
- Not related
Correct answer: 4. Not related
9. For same parameters the PF of the synchronous motor is:
- Better than induction
- Worst than induction
- Identical to induction
- 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:
- 45º
- 60º
- 75º
- 90º
Correct answer: 4. 90º
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