The maximum power developed in a synchronous motor occurs at a coupling angle of
180°
60°
30°
90°
90°
The operating speed of a synchronous motor can be changed to a new fixed value by
changing the load
changing the supply voltage
changing frequency
using brakes
changing frequency
A synchronous motor will always stop when
excitation winding gets disconnected
supply voltage frequency changes
load in motor varies
supply voltage fluctuates
excitation winding gets disconnected
Hunting in a synchronous motor takes place
when load varies
when power factor is unity
when supply voltage fluctuates
motor is under loaded
when load varies
In a synchronous motor which loss varies with load ?
Core loss
Copper loss
Windage loss
Bearing friction loss
Copper loss
A synchronous motor can be made self starting by providing
damper winding on stator as well as rotor poles
none of the above
damper winding on rotor poles
damper winding on stator
none of the above
The oscillations in a synchronous motor can be damped out by
providing damper bars in the rotor pole faces
maintaining constant excitation
running the motor on leading power factors
oscillations cannot be damped
providing damper bars in the rotor pole faces
Synchronous motor always runs at
none of the above
more than synchronous speed
less than synchronous speed
the synchronous speed
the synchronous speed
An over-excited synchronous motor takes
lagging current
both and
leading current
none of the above
leading current
For V-curves for a synchronous motor the graph is drawn between
field current and armature current
armature current and power factor
power factor and field current
terminal voltage and load factor
field current and armature current
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