Explore topic-wise MCQs in Electrical Machines.

This section includes 15 Mcqs, each offering curated multiple-choice questions to sharpen your Electrical Machines knowledge and support exam preparation. Choose a topic below to get started.

1.

IN_A_3-PHASE_SLIP_RING_INDUCTION_MOTOR_HIGH_STARTING_TORQUE_IS_ACHIEVED_BY?$

A. increasing supply voltage
B. increasing supply frequency
C. connecting a capacitor across the motor terminals
D. connecting a star connected resistance across slip ring terminals of motor
Answer» E.
Discussion
2.

The losses that occur in induction motor are$

A. stator copper loss
B. rotor iron loss
C. rotor copper loss
D. all of the mentioned
Answer» B. rotor iron loss
Discussion
3.

In a three-phase induction motor, the starting torque is maximum when$

A. r2 = x2
B. r2 = 1/x2
C. r2 = (x2)<sup>2</sup>
D. r2 = 1 pu
Answer» B. r2 = 1/x2
Discussion
4.

If the rotor circuit resistance is increased in an induction motor, maximum torque will occur at

A. lower speed
B. higher speed
C. same speed
D. none of the mentioned
Answer» B. higher speed
Discussion
5.

The synchronous watt is

A. the torque under which synchronous speed would develop a power of 1 W or power input to rotor in watts
B. shaft output in watts at sub synchronous speed
C. input power to stator at synchronous speed
D. unit rating of synchronous machine
Answer» B. shaft output in watts at sub synchronous speed
Discussion
6.

The rotor power input of 3-phase induction motor is 15 kW at a slip of 5%. The mechanical power developed at the shaft is

A. 14.25 kW
B. 7.5 kW
C. 4 kW
D. 700 W
Answer» B. 7.5 kW
Discussion
7.

In an induction motor, what is the ratio of the rotor copper loss to rotor input?

A. s
B. 1/s
C. 1-s
D. s/(1-s)
Answer» B. 1/s
Discussion
8.

Iron loss in the rotor is negligible. This is due to

A. very low frequency of emf induced in the rotor
B. very low emf induced in the rotor
C. very low flux density in rotor parts
D. laminated core
Answer» B. very low emf induced in the rotor
Discussion
9.

For achieving high starting torque and high operating efficiency an induction motor should have _______ rotor circuit resistance and _______ circuit resistance under operating condition?

A. high, low
B. low, high
C. low, low
D. high, high
Answer» B. low, high
Discussion
10.

The starting torque of the squirrel-cage induction motor is

A. slightly more than full load torque
B. slightly less than full load torque
C. equal to full load torque
D. zero
Answer» B. slightly less than full load torque
Discussion
11.

A 3-phase, 6-pole, 50 Hz induction motor has a full load speed of 960 rpm with its slip rings short circuited. The motor drives the constant load. If the speed is reduced to 800 rpm, then ohmic losses will be

A. 5 times that at full load
B. 0.2 times as that at full load
C. 15 times as that at full load
D. same as that at full load
Answer» B. 0.2 times as that at full load
Discussion
12.

A 3-phasle, 6-pole, 50 Hz induction motor has a full load speed of 960 rpm with its slip rings short circuited. The motor drives the constant load. If the speed is reduced to 800 rpm, then ohmic losses will

A. reduce
B. increase
C. reduce first then becomes constant
D. remains same
Answer» B. increase
Discussion
13.

Rotor ohmic loss is ________ slip.

A. proportional to
B. inverse of
C. inversely proportional to
D. hyperbolic to
Answer» B. inverse of
Discussion
14.

Insertion of external resistance in the squirrel cage induction motor _________ the current, ________ the starting current.

A. reduces, increases
B. increases, reduces
C. increases, increases
D. reduces, reduces
Answer» B. increases, reduces
Discussion
15.

Insertion of external resistance in the squirrel cage induction motor

A. increases torque
B. decreases torque
C. increases torque for some seconds and then decreases
D. does not affect
Answer» B. decreases torque
Discussion