1. The advantage of salient poles in an alternator is ?

reduced windage loss

reduced bearing loads and noise

reduced noise

adaptability of low and medium speed operation

Answer: adaptability of low and medium speed operation

Explanation:


2. Due to which of the following reasons, for aircraft alternators high frequency is used ?

To reduce the bulk

To compensate for high speeds

To compensate for high altitudes

To free the systems from external disturbance

Answer: To reduce the bulk

Explanation:


3. When an alternator is supplying unity power factor load, the armature reaction will produce ?

distortion of the main field

magnetisation of the main field

demagnetisation of the main field

none of the above

Answer: distortion of the main field

Explanation:


4. ln an alternator, the flux created by the armature m.m.f. subtracts directly from the main flux for the following conditions of the load ?

load power factor is unity

load power factor is 0.6 lagging

load power factor is zero lagging

load power factor is zero leading

Answer: load power factor is zero lagging

Explanation:


5. Which harmonic will be totally eliminated in an alternator by using a fractional pitch of 4/5 ?

Third

Fifth

Seventh

Ninth

Answer: Fifth

Explanation:


6. In power generating stations (Thermal stations), The usual number of poles employed in alternators are ?

twenty four

thirty two

forty eight

none of these

Answer: none of these

Explanation:


7. An alternator coupled to which prime mover will usually have the highest rotating speed ?

Steam engine

Reciprocating diesel engine

Francis turbine

Steam turbine

Answer: Steam turbine

Explanation:


8. The speed of a p-pole synchronous machine in r.p.m. is given by ?

120f/p

120p/f

p/?120fp

120fp

Answer: 120f/p

Explanation:


9. In a synchronous machine, all of the following losses are fixed except ?

core loss

copper loss

bearing friction loss

windage loss

Answer: copper loss

Explanation:


10. To obtain sinusoidal flux distribution ?

chamfering of poles is done in turbo alternators only

chamfering of poles is done m salient pole alternators only

either of the above

none of the above

Answer: chamfering of poles is done m salient pole alternators only

Explanation: