Questions and answers for exam Preparation

MCQs

Total Questions : 473 | Page 47 of 48 pages

Question 461. 7. When a single-phase capacitor start induction motor is running at a steady speed delivering a fixed torque, then

peak of forward rotor mmf is equal to the peak of backward rotor mmf
peak of forward stator mmf is equal to the peak of backward stator mmf
net forward rotating flux is equal to the net backward rotating flux
forward flux produced by rotor current is equal to backward flux produced by rotor current

Discuss Question

Answer: Option C. -> net forward rotating flux is equal to the net backward rotating flux

Question 462. 9. If a 3-phasor induction motor and a 1-phase induction motor of the same kW rating and same winding voltage are compared, then

both will be of same size and efficiency
the 3-phase induction motor will be bigger in size and less efficient
the 3-phase induction motor will be smaller in size and more efficient
the 3-phase induction motor will be bigger in size and more efficient

Discuss Question

Answer: Option C. -> the 3-phase induction motor will be smaller in size and more efficient

Question 463. 1. In a 3-phase induction motor, the rotor impedance angle at standstill is 0. The load angle 8 will be

it + 0
?0
? +2
?2

Discuss Question

Answer: Option C. -> ? +2

Question 464. 2. A 3-phase induction motor develops a torque 'T' when driven from a balanced 3-phase supply. The terminal voltage and frequency are halved so that the air-gap flux remains the same while the load torque is kept constant. Then the slip

is reduced to half
remains same as the previous value
speed is reduced to half
speed remains the same

Discuss Question

Answer: Option B. -> remains same as the previous value

Question 465. 3. In a three-phase induction motor with increase in load from light to heavy

both stator and rotor power factor increase
both stator and rotor power factor decrease
stator power factor increases while rotor power factor decreases
stator power factor decreases while rotor power factor increases

Discuss Question

Answer: Option C. -> stator power factor increases while rotor power factor decreases

Question 466. 6. In order to control the speed of a slip ring 3-phase induction motor through injected voltage in its rotor circuit, this voltage and the rotor voltage should essentially be

in same phase
in quadrature
in phase opposition
of same frequency

Discuss Question

Answer: Option D. -> of same frequency

Question 467. 5. The power input to an induction motor is 50kW when it is running at 4% slip. If the stator resistance and core losses are neglected, the rotor copper loss is equal to

38 kW
20 kW
4 kW
2 kW

Discuss Question

Answer: Option C. -> 4 kW

Question 468. 4. The following performance characteris tics are attributed to a 3-phase cage induction motor without skew : 1. lower magnetizing current compared to a slip ring motor.2. low efficiency.3. high pl.4. possible cogging and crawling. Which of these statements are correct?

1, 2 and 3
2, 3 and 4
1, 3 and 4
1, 2 and 4

Discuss Question

Answer: Option D. -> 1, 2 and 4

Question 469. 9. A 3-phase induction motor develops a torque 'T' when driven from a balanced 3-phase supply. The terminal voltage and frequency are halved so that the air-gap flux remains the same while the load torque is kept constant. Then the slip