Induction motor Rotor Voltage Injection MCQ [Free PDF] – Objective Question Answer for Induction motor Rotor Voltage Injection Quiz

11. Calculate the active power in a .89 H inductor.

A. 1.535 W
B. 0 W
C. 2.484 W
D. 1.598 W

Answer: B

The inductor is a linear element. It only absorbs reactive power and stores it in the form of oscillating energy. The voltage and current are 90° in phase in the case of the inductor so the angle between V & I is 90°.

P=VIcos90° = 0 W. 

 

12. Calculate the time period of the waveform i(t)=sin(πt+6π÷4)+sin(πt+5π÷6).

A. 2 sec
B. 4 sec
C. 5 sec
D. 3 sec

Answer: A

The fundamental time period of the sine wave is 2π.

The time period of i(t) is L.C.M {2,2}=2 sec.

The time period is independent of phase shifting and time-shifting. 

 

13. Calculate the total heat dissipated in a rotor resistor of 14.23 Ω when.65 A current flows through it.

A. 6.45 W
B. 6.01 W
C. 6.78 W
D. 6.98 W

Answer: B

The rotor resistor is a linear element. It only absorbs real power and dissipates it in the form of heat. The voltage and current are in the same phase in the case of the resistor so the angle between V & I is 90°.

P=I2R=.65×.65×14.23=6.01 W. 

 

14. Calculate mark to space ratio if the system is on for 4.3 sec and off for 78.2 sec.

A. .054
B. .047
C. .039
D. .018

Answer: A

Mark to space is Ton÷Toff. It is the ratio of the time for which the system is active and the time for which is inactive.

M = Ton÷Toff = 4.3÷78.2 = .054. 

 

15. In the rotor voltage injection method, when an external voltage source is in phase with the main voltage then speed will ___________

A. Increase
B. Decrease
C. Remain unchanged
D. First increases then decrease

Answer: A

In the rotor injection method, when an external voltage is in phase with the main voltage net voltage increases and the value of slip decreases, and the value of rotor speed increases. 

 

16. A 2-pole, 3-phase, ______ Hz induction motor is operating at a speed of 550 rpm. The frequency of the rotor current of the motor in Hz is 2.

A. 9.98
B. 9.71
C. 9.12
D. 9.37

Answer: D

Given a number of poles = 2.

The rotor speed is 550 rpm.

Ns=120×f÷P=120×f÷2 = 60f rpm.

S=Ns-Nr÷Ns. F2=sf. S=F2÷f.

The supply frequency is 9.37 Hz. 

 

17. Calculate the average value of the sinusoidal waveform x(t)=848sin(1.65πt+2π÷0.68).

A. 0
B. 78 V
C. 15 V
D. 85 V

Answer: A

The sinusoidal waveform is generally expressed in the form of

V=Vmsin(Ωt+α)

where

Vm represents peak value
Ω represents angular frequency
α represents a phase difference.

The average value of a sine wave is zero because of equal and opposite lobes areas. 

 

18. R.M.S value of the periodic square waveform of amplitude 72 V.

A. 72 V
B. 56 V
C. 12 V
D. 33 V

Answer: A

R.M.S value of the periodic square waveform is Vm and r.m.s value of the trapezoidal waveform is Vm÷3½.

The peak value of the periodic square waveform is Vm. 

 

19. In the rotor voltage injection method, when an external voltage source is in the opposite phase to the main voltage then speed will ___________

A. Increase
B. Decrease
C. Remain unchanged
D. First increases then decrease

Answer: B

In the rotor injection method, when an external voltage is in the opposite phase to the main voltage net voltage decreases and the value of slip increases, and the value of rotor speed decreases. 

 

20. The rotor injection method is a part of the slip-changing technique.

A. True
B. False

Answer: A

The rotor injection method comes under the slip changing technique. It uses an external voltage source to change the slip value. The load torque remains constant here. 

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