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.Management Sciences
Category: Synchronous Motors
The back e.m.f. in the stator of a synchronous motor depends on____________?
A. number of poles
B. flux density
C. rotor speed
D. rotor excitation
E. none of the above
The efficiency of a properly designed synchronous motor will usually fall in range___________?
A. 60 to 70%
B. 75 to 80%
C. 85 to 95%
D. 99 to 99.5%
A synchronous motor can be started by________?
A. pony motor
B. D.C. compound motor
C. providing damper winding
D. any of the above
When the excitation of an unloaded salient pole synchronous motor suddenly gets disconnected______________?
A. the motor stops
B. it runs as a reluctance motor at the same speed
C. it runs as a reluctance motor at a lower speed
D. none of the above
In a synchronous motor, the magnitude of stator back e.m.f. Eb depends on___________?
A. load on the motor
B. d.c. excitation only
C. both the speed and rotor flux
D. none of the above
By which of the following methods the constant speed of a synchronous motor can be changed to new fixed value ?
A. By changing the supply frequency
B. By interchanging any two phases
C. By changing the applied voltage
D. By changing the load
The maximum torque which a synchronous motor will develop at rest for any angular position of the rotor, at rated stator supply voltage and frequency, is known as__________?
A. locked-rotor torque
B. synchronous torque
C. pull up torque
D. reluctance torque
For V-curves for a synchronous motor the graph is drawn between:_______________?
A. armature current and power factor
B. terminal voltage and load factor
C. power factor and field current
D. field current and armature current
An over-excited synchronous motor takes__________?
A. leading current
B. lagging current
C. both A. and (b)
D. none of the above
The angle between the rotating stator flux and rotor poles is called _________ angle.
A. synchronizing
B. obtuse
C. torque
D. power factor
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