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Polyphase Induction Motors - Interview Questions and Answers

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46. Blocked rotor test on induction motors is used to find out
A. leakage reactance
B. power factor on short circuit
C. short-circuit current under rated voltage
D. all of the above
Explanation:
47. A 500 kW, 3-phase, 440 volts, 50 Hz, A.C. induction motor has a speed of 960 r.p.m. on full load. The machine has 6 poles. The slip of the machine will be
A. 0.01
B. 0.02
C. 0.03
D. 0.04
Explanation:
48. The torque of a rotor in an induction motor under running condition is maximum
A. at the unit value of slip
B. at the zero value of slip
C. at the value of the slip which makes rotor reactance per phase equal to the resistance per phase
D. at the value of the slip which makes the rotor reactance half of the rotor
Explanation:
49. 5 H.P., 50-Hz, 3-phase, 440 V, induction motors are available for the following r.p.m. Which motor will be the costliest ?
A. 730 r.p.m.
B. 960 r.p.m.
C. 1440 r.p.m.
D. 2880 r.p.m.
Explanation:
50. In three-phase induction motors sometimes copper bars are placed deep in the rotor to
A. improve starting torque
B. reduce copper losses
C. improve efficiency
D. improve power factor
Explanation:
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