MCQ on Alternator – 3

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 1. The speed of alternator at supply frequency 50 Hz will maximum if it is wound for
(a) 2 poles.
(b) 4 poles.
(c) 6 poles.
(d) 8 poles.

 2. The armature reaction of an alternator influences
(a) rotor speed.
(b) terminal voltage per phase.
(c) frequency of armature current.
(d) generated voltage per phase.

 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. When the excitation of salient pole alternator is reduced, the voltage induced in the stator winding will be
(a) decreases.
(b) same.
(c) increases.
(d) increase slightly.

 5. The leakage reactance of a three phase alternator is determine by performing
(a) open-circuit and zero power factor tests.
(b) zero power factor and slip tests.
(c) open and short circuit tests.
(d) short circuit and slip tests.

 6. The short circuit characteristics of an alternator is
(a) parabolic.
(b) linear.
(c) nonlinear.
(d) none of the above.

 7. When two alternators are running in exactly synchronism, the synchronising power wil be
(a) zero.
(b) sum of the output of two.
(c) unity.
(d) 0.707.

 8. Non salient pole rotor are prefered for
(a) low speed application.
(b) high speed application.
(c) both low and high speed application.
(d) none of the above.

 9. If the load on and alternator changes, the change in its terminal voltage depends upon
(a) amount of excitation.
(b) magnitude of the load current.
(c) power factor of the load.
(d) all of the above.

 10. The rotor of the salient pole alternator has 24 poles. The number of cycles of emf in one revolution would be
(a) 24.
(b) 12.
(c) 6.
(d) 4.

 11. A leading pf load on an alternator implies that its voltage regulation shall be
(a) positive.
(b) negative.
(c) zero.
(d) any one of these.

 12. For the same power rating, a lower voltage alternator will be
(a) more efficient.
(b) larger in size.
(c) operating at high rpm.
(d) more costly.

 13. For unity power factor load, the effect of armature reaction in alternator will be
(a) cross magnetising.
(b) magnetising.
(c) di-magnetising.
(d) none of the above.

 14. Which parameter of an alternator is found by zero power factor method
(a) voltage drop due to armature reaction.
(b) armature reaction mmf.
(c) leakage resistance drop.
(d) all of the above.

 15. In an alternator, short circuit current is limited by the
(a) saturated synchronous impedence.
(b) unsaturated synchronous impedence.
(c) neutral synchronous impedence.
(d) none of the above.

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