Synchronous Generator MCQs Part 14
Contents
- 1 Armature windings of an alternator are generally
- 2 If the excitation to an alternator connected to an infinite busbar is changed
- 3 The voltage regulation of an alternator for PF of 0.8 lagging is X at unity PF
- 4 The voltage regulation of an alternator supplying power to a load with a leading power factor always is
- 5 A 3 phase, 32 pole alternator has star-connected winding having 120 slots
Armature windings of an alternator are generally
Armature windings of an alternator are generally
- Open windings
- Closed windings
- Partly open and partly closed windings
- None of the above
Correct answer: 1. Open windings
If the excitation to an alternator connected to an infinite busbar is changed
If the excitation to an alternator connected to an infinite busbar is changed while keeping the power input to its prime-mover unchanged, then which of following is correct:
- Kva output will change
- Kvar output will change
- Power factor will change
- All of these
Correct answer: 4. All of these
The voltage regulation of an alternator for PF of 0.8 lagging is X at unity PF
The voltage regulation of an alternator for PF of 0.8 lagging is X at unity PF:
- Smaller than
- Greater than
- The same as
- None of the above
Correct answer: 2. Greater than
The voltage regulation of an alternator supplying power to a load with a leading power factor always is
The voltage regulation of an alternator supplying power to a load with a leading power factor always is:
- Zero
- Positive
- Negative
- Unity
Correct answer: 3. Negative
A 3 phase, 32 pole alternator has star-connected winding having 120 slots
A 3 phase, 32 pole alternator has star-connected winding having 120 slots and 10 conductors per slot. The flux per is 30 mWb that is sinusoidally distributed and the speed is 375 RPM. The line EMF is:
- 1538 Hz
- 2307 Hz
- 3076 Hz
- 4614 Hz
Correct answer: 4. 4614 Hz
Explanation:
Line EMF = √3 * Generated EMF per phase
Generated EMF per phase = 2.22 fZΦ = 2.22
Where Z = No of conductors per phase = No of slots per phase * No of conductors per slot
Number of slots per phase = 120/3 = 40
Number of conductors per phase (Z) = 40 * 10 = 400
Formula for frequency (f) = NP/120 = (375 * 32)/120 = 100 Hz
————
Now Generated EMF per phase = 2.22 fZΦ = 2.22 * 100 * 400 * 30 * 10^-3 = 2664 V
————
Line EMF = √3 * Generated EMF per phase = √3 * 2664 = 4614 V