Change of D.C. excitation of a synchronous motor changes
any of the above
power factor of power drawn by the motor
applied voltage of the motor
motor speed
power factor of power drawn by the motor
When the excitation of an unloaded salient pole synchronous motor suddenly gets disconnected
the motor stops
it runs as a reluctance motor at the same speed
it runs as a reluctance motor at a lower speed
none of the above
the motor stops
When V is the applied voltage then the breakdown torque of a synchronous motor varies as
1/V
V2
V312
V
V
A synchronous motor running with normal excitation adjusts to load increases essentially by increase in
back e.m.f.
power factor
armature current
torque angle
armature current
A synchronous motor has better power factor as compared to that of an equivalent induction motor. This is mainly because
stator supply is not required to produce magnetic field
synchronous motor has large airgap
mechanical load on the rotor remains constant
synchronous motor has no slip
stator supply is not required to produce magnetic field
A synchronous motor working at leading power factor can be used as
phase advancer
noise generator
voltage booster
mechanical synchronizer
phase advancer
The power developed by a synchronous motor will be maximum when the load angle is
120°
90°
zero
45°
90°
Mostly synchronous motors are of
salient pole type machines
alternator type machines
induction type machines
smooth cylindrical type machines
salient pole type machines
The synchronous motor is not inherently self-starting because
the rotating magnetic field is produced by only 50 Hz frequency currents
a rotating magnetic field does not have enough poles
the starting device to accelerate the rotor to near synchronous speed is absent
the force required to accelerate the rotor to the synchronous speed in an instant is absent
the force required to accelerate the rotor to the synchronous speed in an instant is absent
As the load is applied to a synchronous motor the motor takes more armature current because
the increased load has to take more current
the back e.m.f. decreases causing an increase in motor current
the rotor by shifting its phase backward causes motor to take more current
the rotor strengthens the rotating field casuing more motor current
the rotor by shifting its phase backward causes motor to take more current
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