Solid Sate AC Drives MCQ [Free PDF] – Objective Question Answer for Solid Sate AC Drives Quiz

21. Increasing the stator poles ___________ the speed of Reluctance motor.

A. Decreases
B. Increases
C. Remains the same
D. Negative

Answer: A

Increasing the stator poles decreases the speed of the Reluctance motor. The rotating magnetic field is developed which rotates at the speed of Ns. Ns∝(1÷P). 

 

22. Calculate the circuit turn-off time for 3-Φ Fully controlled rectifier if the firing angle is 27° and the supply frequency is 50 Hz.

A. 11.8 msec
B. 14.4 msec
C. 16.1 msec
D. 16.5 msec

Answer: A

The circuit turn-off time for 3-Φ Fully controlled rectifier is (240°-α)÷ω. The value of circuit turn-off time for ∝ < 60° is

(240°-27°)÷6.28×50=11.8 msec. 

 

23. Calculate the circuit turn-off time for 3-Φ Fully controlled rectifier if the firing angle is 120° and the supply frequency is 60 Hz.

A. 1.8 msec
B. 3.2 msec
C. 6.3 msec
D. 2.7 msec

Answer: D

The circuit turn-off time for 3-Φ Fully controlled rectifier is (180°-α)÷ω. The value of circuit turn-off time for ∝ ≥ 60° is

(180°-120°)÷6.28×60=2.7 msec. 

 

24. Calculate peak-peak voltage if Vmax=180 V and Vmin=60 V.

A. 120 V
B. 150 V
C. 170 V
D. 110 V

Answer: A

Peak-Peak voltage is equal to the difference between the maximum and minimum voltage. It is mathematically represented as

Vp-p=Vmax-Vmin=180-60=120 V. 

 

25. Calculate the value of the Crest factor if Vpeak=798 V and Vr.m.s=489 V.

A. 1.63
B. 1.54
C. 1.59
D. 1.26

Answer: A

The value of the crest factor is
Vpeak÷Vr.m.s=798÷489=1.63 V.

It signifies the peak value is 1.63 times the r.m.s value. 

 

26. Reluctance motor operates at power factor of __________

A. .8
B. .2
C. .3
D. .9

Answer: A

The reluctance motor operates at a power factor of .8. The Reluctance motor works on the principle of an Induction motor. 

 

27. Calculate the reactive power in a 24.5 Ω resistor.

A. 0 VAR
B. 5 VAR
C. 8 VAR
D. 9 VAR

Answer: A

The 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 0°. Q = VIsin0 = 0 VAR. 

 

28. Calculate the value of the duty cycle if the system is on for 1 sec and off for 17 sec.

A. .055
B. .781
C. .484
D. .947

Answer: A

The duty cycle is Ton÷Ttotal. It is the ratio of the time for which the system is active and the time taken by the signal to complete one cycle.

D = Ton÷Ttotal=1÷18=.055. 

 

29. Calculate mark to space ratio if the system is on for 4 sec and off time is 9 sec.

A. .54
B. .44
C. .45
D. .46

Answer: B

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÷(9) = .44. 

 

30. Calculate the value of the frequency if the inductive reactance is 60 Ω and the value of the inductor is 4 H.

A. 2.38 Hz
B. 5.54 Hz
C. 4.65 Hz
D. 9.42 Hz

Answer: A

The frequency is defined as the number of oscillations per second. The frequency can be calculated using the relation

XL = 2×3.14×f×L. F
= XL÷2×3.14×L
= 60÷2×3.14×4 = 2.38 Hz. 

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