The working of a synchronous motor is similar to
transmission of mechancial power by shaft
turbine
distribution transformer
gear train arrangement
transmission of mechancial power by shaft
The minimum armature current of the synchronous motor corresponds to operation at
unity power factor
0.707 power factor lagging
zero power factor leading
0.707 power factor leading
unity power factor
In a synchronous motor the magnitude of stator back e.m.f. £& depends on
both the speed and rotor flux
d.c. excitation only
speed of the motor
load on the motor
d.c. excitation only
If load (or torque) angle of a 4-pole synchronous motor is 6° electrical its value in mechanical degrees is
3
2
4
6
3
The shaft of synchronous motor is made of
stainless steel
alnico
chrome steel
mild steel
mild steel
When the field of a synchronous motor is under-excited the power factor will be
leading
unity
lagging
zero
lagging
The speed regulation of a synchronous motor is always
zero
positive
0.005
0.01
zero
The percentage slip in case of a synchronous motor is
zero
1
0.01
0.005
zero
When load on an over-excited or under excited synchronous*motor is increased rate of change of its armature current as compared with that of power factor is
twice
less
more
equal
less
The rotor copper losses in a synchronous motor are met by
d.c. source
armature input
motor input
supply lines
d.c. source
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