Practice Test: Question Set - 10
1. For power factor correction, synchronous motors operate at
- (A) No-load and greatly overexcited fields
- (B) No-load and under-excited fields
- (C) Normal load with minimum excitation
- (D) Normal load with zero excitation
2. Under which of the following conditions hunting of synchronous motor is likely to occur?
- (A) Periodic variation of load
- (B) Over-excitation
- (C) Overloading for long periods
- (D) Small and constant load
3. A synchronous machine with low value of short-circuit ratio has
- (A) Lower stability limit
- (B) High stability limit
- (C) Good speed regulation
- (D) Good voltage regulation
4. The back e.m.f. of a synchronous motor depends on
- (A) Speed
- (B) Load
- (C) Load angle
- (D) All of the above
5. In which of the following motors the stator and rotor magnetic field rotate at the same speed?
- (A) Universal motor
- (B) Synchronous motor
- (C) Induction motor
- (D) Reluctance motor
6. The angle between the rotating stator flux and rotor poles is called _________ angle.
- (A) Torque
- (B) Obtuse
- (C) Synchronizing
- (D) Power factor
7. When a 3-phase synchronous generator is supplying a zero power factor lagging load, the armature field affects the main field in the following way
- (A) Augments it directly
- (B) Directly opposes it
- (C) Cross-magnetizes it
- (D) None of the above
8. In a 3-phase synchronous motor, the negative phase sequence exists when the motor is
- (A) Supplied with unbalanced voltage
- (B) Under-loaded
- (C) Overloaded
- (D) None of the above
9. Which of the following motors is non-self starting?
- (A) D.C. series motor
- (B) Synchronous motor
- (C) Squirrel cage induction motor
- (D) Wound round induction motor
10. The minimum armature current of the synchronous motor corresponds to operation at
- (A) Zero power factor leading
- (B) Unity power factor
- (C) 0.707 power factor lagging
- (D) 0.707 power factor leading
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