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.Management Sciences
Category: Synchronous Motors
In which of the following motors the stator and rotor fields rotate simultaneously?
A. D.C. motor
B. Reluctance motor
C. Universal motor
D. Synchronous motor
E. Induction motor
Synchronous motor always runs at______________?
A. the synchronous speed
B. less than synchronous speed
C. more than synchronous speed
D. none of the above
In a 3-phase, 4-pole, 50 Hz synchronous motor, the frequency, pole number and load torque all are halved. The motor speed will be____________?
A. 3000 r.p.m.
B. 1500 r.p.m.
C. 750 r.p.m.
D. none of the above
When a 3-phase synchronous generator is supplying a zero power factor lagging load, the armature field affects the main field in the following way
A. augments it directly
B. directly opposes it
C. cross-magnetises it
D. none of the above
Synchronous motors are generally not self-starting because:
A. the direction of rotation is not fixed
B. the direction of instantaneous torque reverses after half cycle
C. startes cannot be used on these machines
D. starting winding is not provided on the machines
A 3-phase synchronous motor is running clockwise. If the direction of its field current is reversed
A. the motor will stop
B. the motor continue to run in the same direction
C. the winding of the motor will burn
D. the motor will run in the reverse direction
E. none of the above
While starting a salient pole synchronous motor by induction motor action and connecting field discharge resistance across field, starting and accelerating torque is produced by_____________?
A. induction motor torque in field winding
B. induction motor torque in damper winding
C. eddy current and hysteresis torque in pole faces
D. reHetance motor torque due to saliency of the rotor
E. all of the above methods
A synchronous machine with low value of short-circuit ratio has___________?
A. lower stability limit
B. high stability limit
C. good speed regulation
D. good voltage regulation
E. none of the above
Exciters of synchronous machines are______________?
A. d.c. series machines
B. d.c. shunt machines
C. d.c. compound machines
D. any of the above
A synchronous motor is running on a load with normal excitation. Now if the load on the motor is increased
A. power factor as well as armature current will decrease
B. power factor as well as armature current will increase
C. power factor will increase but armature current will decrease
D. power factor will decrease and armature current will increase
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