Synchronous motors

23. If excitation of a synchronous motor running with a constant load is decreased from its normal value, ignoring effects of armature reaction, it leads to

increase in both armature current and power factor angle
increase in back e.m.f. but decrease in armature current
increase in both armature current and power factor which is lagging
increase in torque angle but decrease in back e.m.f.

Detailed SolutionIf excitation of a synchronous motor running with a constant load is decreased from its normal value, ignoring effects of armature reaction, it leads to

27. While starting a salient pole synchronous motor by induction motor action and connecting field discharge resistance across field, starting and accelerting torque is produced by

induction motor torque in field winding
induction motor torque in damper winding
eddy current and hysteresis torque in pole faces
reHetance motor torque due to saliency of the rotor E. all of the above methods

Detailed SolutionWhile starting a salient pole synchronous motor by induction motor action and connecting field discharge resistance across field, starting and accelerting torque is produced by

29. A synchronous motor has better power factor as compared to that of an equivalent induction motor. This is mainly because

synchronous motor has no slip
stator supply is not required to produce magnetic field
mechanical load on the rotor remains constant
synchronous motor has large airgap

Detailed SolutionA synchronous motor has better power factor as compared to that of an equivalent induction motor. This is mainly because

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