Induction Machines - Electrical Engineering (MCQ) questions and answers

1)   While delivering an useful power of 20 kW to the full load, a 3 phase, 50 Hz, 6 pole induction motor draws a line current of 50 A. it is connected to supply of 420 V and runs at a speed of 950 rpm. If mechanical losses are 1000 W, then its rotor copper losses and shaft torque are

a. 1105.26 W, 201.03 N-m
b. 1125.26 W, 201.03 N-m
c. 1105.26 W, 208.09 N-m
d. 1125.26 W, 208.09 N-m
Answer  Explanation 

ANSWER: 1105.26 W, 201.03 N-m

Explanation:
No explanation is available for this question!
2)   The NO contact and NC contact of D.O.L. starter is normally

a. Open, closed
b. Closed, open
c. Open, open
d. Closed, closed
Answer  Explanation 

ANSWER: Open, closed

Explanation:
No explanation is available for this question!
3)   In washing machines, most commonly used motors are

a. Split phase induction motors
b. Slip ring induction motors
c. Capacitor start induction motors
d. Shaded pole induction motors
Answer  Explanation 

ANSWER: Split phase induction motors

Explanation:
No explanation is available for this question!
4)   For a three phase induction motor, the two rotor frequencies are given by

a. sf, (1 - s) f
b. sf, (2 - s) f
c. (1 - s) f, (2 - s) f
d. Sf , sf
Answer  Explanation 

ANSWER: sf, (2 - s) f

Explanation:
No explanation is available for this question!
5)   A 3 phase induction motor in a short circuit current is equal 3 times of the full load current. If the full load slip is 2%, then the starting torque as a percentage of full load torque is

a. 6% of full load torque
b. 18% of full load torque
c. 36% of full load torque
d. None of these
Answer  Explanation 

ANSWER: 18% of full load torque

Explanation:
No explanation is available for this question!
6)   In terms of slip, the actual speed (N) of the induction motor can be expressed as

a. Ns (1-s)
b. Ns (s-1)
c. Ns / (1-s)
d. Ns / (s-1)
Answer  Explanation 

ANSWER: Ns (s-1)

Explanation:
No explanation is available for this question!
7)   A 50 Hz, 3 phase induction motor with 4 pole stator is supplied by mains, which contains a pronounced fifth time harmonic. The speed of the fifth space harmonic will be

a. 100 rpm
b. 300 rpm
c. 600 rpm
d. 7500
Answer  Explanation 

ANSWER: 300 rpm

Explanation:
No explanation is available for this question!
8)   For moment of inertia to be small in two phase servomotor, the ratio of rotor diameter to its length should be

a. Equal to 1
b. small
c. large
d. All of these
Answer  Explanation 

ANSWER: small

Explanation:
No explanation is available for this question!
9)   A two phase servomotor is commonly used in feedback control system to drive the loads and as sensors to measure

a. Speed of controlled element
b. Position of controlled element
c. Both (a) and (b)
d. None of these
Answer  Explanation 

ANSWER: Both (a) and (b)

Explanation:
No explanation is available for this question!
10)   The flux under the unshaded pole of shaded pole induction motor

a. Is in equal phase of flux under the shaded pole
b. Lags the flux under the shaded pole
c. Leads the flux under the shaded pole
d. None of these
Answer  Explanation 

ANSWER: Leads the flux under the shaded pole

Explanation:
No explanation is available for this question!
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