MCQs on Electrical Machines

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01․ A smaller air gap in a polyphase induction motor helps to
reduce the chance of cogging.
reduce the magnetizing current.
increase the starting torque.
reduce the chance of crawling.

Under construction.
02․ In a 3 - Φ induction motor
power factor at starting is high as compared to that while running.
power factor at starting is low as compared to that while running.
power factor at starting in the same as that while running.
none of them.

Under construction.
03․ A 3 - Φ slip ring motor has
double cage rotor.
short-circuited rotor.
wound rotor.
any of the above.

Under construction.
04․ Skewing of the rotor in a 3 - Φ squirrel cage induction motor reduces
noise, parasitic torque, starting torque and pull out torque.
noise and parasitic torque, but increase starting and pull-out torque.
noise and pullout torque, but increase parasitic and starting torque.
noise, parasitic and starting torque, but increase pull out torque.

Under construction.
05․ The 3 - Φ induction motor with rotor circuit open will
run normally.
make noise.
not run.
get over heated.

Under construction.
06․ The principle of operation of a 3 - Φ induction motor is almost similar to that of
synchronous motor.
capacitor start induction motor.
repulsion start induction motor.
transformer with secondary short circuited.

Under construction.
07․ Two of supply terminals to a 3 - Φ induction motor get interchanged during re-connection after normal maintenance. When switched on the supply, the motor will
not start at all.
get heated and damaged.
rotate in the same direction as before maintenance.
rotate in direction opposite to that before maintenance.

Under construction.
08․ The mmf produced by rotor currents of a 3 - Φ induction motor
rotates at the speed of rotor in the air gap.
is at standstill with respect to stator mmf.
rotates at slip speed with respect to stator mmf.
rotates at synchronous speed with respect to rotor.

Under construction.
09․ At the instant of starting, the per unit slip of 3 - Φ induction motor is
0.05.
0.1.
1.0.
0.5.

Under construction.
10․ The direction of rotation of a 3 - Φ induction motor can be reversed by
transposing any two leads from supply.
transposing any two leads from slip rings.
transposing all the three leads from the supply.
disconnecting any one phase.

Under construction.
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