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Electrical Engineering Objective Questions { Alternators }

1. For turbo-alternators, the usual value of pole number is
D. none of these

2. Under no-load condition power drawn by the prime mover of an alternator goes to
A. produce induced emf in armature winding
B. meet no-load losses
C. produce power in armature
D. meet Cu losses both in armature and rotor windings

3. As load p.f. of an alternator becomes more leading, the value of generated voltage required to give rated terminal voltage
A. increases
B. remains unchanged
C. decreases
D. varies with rotor speed

4. In an alternator running with a balanced zero p.f. lagging load, phase difference between the resultant armature (or stator) flux and main field flux is always.
B. zero
C. 90? leading
D. 90? lagging

5. At lagging loads, armature reaction in an alternator is
A. cross-magnetising
B. demagnetizing
C. non-effective
D. magnetising

6. Synchronous impedance method of finding voltage regulation of an alternator is called pessimistic method because
A. it was first suggested by Dr. Pessimist of Depression Island in Indian ocean.
B. armature reaction is wholly magnetizing
C. it is the simplest to perform, compute and comprehend
D. it given regulation value higher than is actually found by direct loading

7. If chording angle for fundamental flux wave is a, its value for 5th harmonic is
A. 5 a
B. a/5
C. 25 a
D. a125

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