# MCQs on Electrical Machines

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01․ A 4 pole 50 Hz 1-phase induction motor is running at 1470 rpm. Find the forward and backward slips?
0.02, 1.98
0.04, 1.96
0.02, 0.98
0.04, 0.96

02․ If we increase the rotor reactance value, the maximum torque will
increase
decrease
not changed
none of the above

Therefore, if we increase the rotor reactance value, then maximum torque will decrease.

slightly increase.
slightly decrease.
not change.
none of the above.

Under no load condition the motor speed is Ns i.e., Nr = Ns. As load increases the speed will decrease. Therefore the slip will increase slightly. Practically slip varies from 1% to 4% from no load to full load.

04․ A 440 V, 3-phase, 10 pole and 50 HZ synchronous motor delivering a torque of 50 N-m, delivers a power of
500W
1000W
3000W
100W

05․ A 3-phase, 50 Hz, 4 pole induction motor is running at 1440 rpm and rotor input power is 2KW. Find the rotor copper loss?
40W
60W
80W
100W

06․ A 3-phase, 50Hz, 4 pole induction motor is running at 1440 rpm and rotor input power is 2KW. Find the rotor output power?
2000W
1450W
1820W
1920W

07․ A 3-phase, 50 Hz, 4 pole induction motor is running at 1440 rpm. Find the rotor efficiency?
96%
92%
94%
95%

08․ Torque developed in the rotor is
directly proportional to slip
inversely proportional to slip
either of these
not dependent on the slip

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

Air gap sends the power from stator to rotor. If the air gap between stator and rotor is more, stator will draw more magnetizing current from the supply in order to establish the rotating magnetic field in the air gap between the stator and rotor. As the airgap offers high reluctance and low permeability to the flux required by the rotor, it requires more magnetizing current. To avoid this condition, smaller air gaps are used in between stator and rotor.

10․ No load test on induction motor is conducted to find which of the following losses?
Stator core loss
Stator copper loss
Rotational loss
All of the above

In no load test the motor runs freely on no-load by applying rated voltage across its stator and no load power consumption is measured by two watt-meter method. No load power consumption is nothing but no-load losses, which are stator core loss, stator copper loss due to no load current and rotational losses.

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