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Practice Test: Question Set - 09


1. It is advisable to avoid line starting of induction motor and use starter because
    (A) It will run in reverse direction
    (B) It will pick up very high speed and may go out of step
    (C) Motor takes five to seven times its full load current
    (D) Starting torque is very high

2. 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

3. An induction motor is identical to
    (A) D.C. compound motor
    (B) D.C. series motor
    (C) Synchronous motor
    (D) Asynchronous motor

4. Slip rings are usually made of
    (A) Copper
    (B) Carbon
    (C) Phosphor bronze
    (D) Aluminium

5. The 'crawling" in an induction motor is caused by
    (A) High loads
    (B) Low voltage supply
    (C) Improper design of machine
    (D) Harmonics developed in the motor

6. Which is of the following data is required to draw the circle diagram for an induction motor?
    (A) Block rotor test only
    (B) No load test only
    (C) Block rotor test and no-load test
    (D) Block rotor test, no-load test and stator resistance test

7. 5 H.P., 50Hz, 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.

8. For driving high inertia loads best type of induction motor suggested is
    (A) Slip ring type
    (B) Squirrel-cage type
    (C) Any of the above
    (D) None of the above

9. A 3-phase 440 V, 50 Hz induction motor has 4% slip. The frequency of rotor e.m.f. will be
    (A) 200 Hz
    (B) 50 Hz
    (C) 2 Hz
    (D) 0.2 Hz

10. What will happen if the relative speed between the rotating flux of stator and rotor of the induction motor is zero?
    (A) The slip of the motor will be 5%
    (B) The rotor will not run
    (C) The rotor will run at very high speed
    (D) The torque produced will be very large

11. The efficiency of an induction motor can be expected to be nearly
    (A) 60 to 90 %
    (B) 80 to 90 %
    (C) 95 to 98 %
    (D) 99 %

12. The number of slip rings on a squirrel cage induction motor is usually
    (A) Two
    (B) Three
    (C) Four
    (D) None

13. A 3-phase induction motor delta connected is carrying too heavy load and one of its fuses blows out. Then the motor
    (A) Will continue running burning its one phase
    (B) Will continue running burning its two phase
    (C) Will stop and carry heavy current causing permanent damage to its winding
    (D) Will continue running without any harm to the winding

14. The crawling in the induction motor is caused by
    (A) Low voltage supply
    (B) High loads
    (C) Harmonics developed in the motor
    (D) Improper design of the machine

15. It is advisable to avoid line-starting of induction motor and use starter because
    (A) Motor takes five to seven times its full load current
    (B) It will pickup very high speed and may go out of step
    (C) It will run in reverse direction
    (D) Starting torque is very high

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