SYNCHRONOUS MACHINES

SYNCHRONOUS MACHINES

Q.The damper winding in the synchronous moor is often used to

a) prevent hunting only
b) prevent hunting & provide the starting toque
c) maintain synchronism
d) provide the starting torque only.

Ans. b

Q.Which of the following statements is true?
Short-pitched coils in the alternators are used to

a) reduce the size of the machine
b) reduce the harmonics or to eliminate the harmonics from the generated emf
c) provide accurate phase difference of 120 degrees between phases
d) reduce copper losses.

Ans. b

Q.The armature flux of an alternator at unity power factor load will be
a) demagnetizing
b) of square waveform
c) cross-magnetizing

Ans. c

Q.The armature reaction of an alternator will be completely magnetizing when load power factor is

a) unity
b) zero lagging
c) zero leading
d) 0.8 lagging

Ans. c

Q.If two alternators are running in parallel and he voltage of one machine is suddenly increased

a) the machine winding will burn
b) both machines will stop
c) synchronizing torque will be produced to restore synchronism

Ans. c

6If the input to the prime mover of an alternator ( in a system of three alternators) is kept constant, and the excitation is changed, then

(Q) the reactive component of the output is changed
(Q.) the active component of the output is changed
(Q.) the power factor of the load remains the same
(Q.) (a) and (b) occur simultaneously.

Ans. a

Q.The coupling angle or load angle of a synchronous motor is defined as the angle between the

a) rotor and the stator poles of same polarity
b) rotor and the stator poles of opposite polarity
c) rotor and stator teeth

Ans. b