A. pulling the motor directly on line without a starter
B. locking of rotor due to harmonics
C. starting the motor on load which is more than the rated load
D. interchanging two supply phases for quick stopping
Related Mcqs:
- 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. - 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 - In case of the induction motors the torque is___________?
A. inversely proportional to (Vslip)
B. directly proportional to (slip)2
C. inversely proportional to slip
D. directly proportional to slip - In medium sized induction motors, the slip is generally around___________?
A. 0.04%
B. 0.4%
C. 4%
D. 14% - In squirrel cage induction motors, the rotor slots are usually given slight skew in order to__________?
A. reduce windage losses
B. reduce eddy currents
C. reduce accumulation of dirt and dust
D. reduce magnetic hum - DOL starting of induction motors is usually restricted to_____________?
A. low horsepower motors
B. variable speed motors
C. high horsepower motors
D. high speed motors - Which type of bearing is provided in small induction motors to support the rotor shaft ?
A. Ball bearings
B. Cast iron bearings
C. Bush bearings
D. None of the above - 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 - In a three-phase induction motor, the number of poles in the rotor winding is always__________?
A. zero
B. more than the number of poles in stator
C. less than number of poles in stator
D. equal to number of poles in stator - 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
