127. If the load of a synchronous motor is increases while keeping the field excitation constant, then

A. power factor will increase and power angle will decrease

B. power factor will decrease and power angle will increase

C. both power factor and power angle will increase

D. both power factor and power angle will decrease

128. A synchronous motor operates as a synchronous condensor when it is

A. operated at unity power factor

B. under-excited

C. over-excited

D. connected in parallel with condensors

129. The reluctance power of a salient-pole synchronous motor does not depend upon the field excitation but on the degree of saliency. The expression for reluctance power is (the terms have their usual meanings.V2 (Xd?Xq )

A. sin 28

B. 2V2Xd ?Xq )sin 8Xd Xq, (Xd?Xq)

C. 2V-sin 28 Xd XqV2 (Xd?Xq)

D. sin 82Xd Xq

130. The field winding of a 3-phase synchronous motor is short-circuited directly. If a 3-phase balanced voltage is impressed across the stator terminals,then the rotor will

A. rotate at synchronous speed

B. rotate at a speed slightly less than synchronous speed

C. rotate at a speed very near to half the synchronous speed

D. not rotate at all

131. A 3-phase synchronous motor with negligible losses is connected to the supply at rated frequency and constant terminal voltage 'V'. The induced emf of the motor is designated as E. If the motor is now gradually loaded to its rated power, adjusting its excitation to obtain, say 0.8 leading power factor operation, then E-phasor would

A. be less than V-phasor and also lead V-phasor

B. be greater than V-phasor and also lead V-phasor

C. be less than V-phasor and also lag V-phasor

D. be greater than V-phasor and also lag V-phasor

132. The field current of a synchronous motor is increased while its load it constant. How will its power angle and power factor change?

A. Power angle decreases and power factor improves

B. Power angle remains same throughout but power factor improves

C. Power angle increases while its power factor gradually decreases

D. Power angle and power factor both increase

133. A synchronous motor runs at only one speed (i.e. synchronous speed) because it

A. has no losses

B. is a doubly fed machine

C. has a damper winding

D. none of the above

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