Electrical Machines - Induction Motors

Questions from SSC J.E. 2017 Exam

1. The speed of the rotating magnetic field in an induction motor is known as the
(a) Slip speed 
(b) Effective speed
(c) Shaft speed 
(d) Synchronous speed

2. When the frequency of the rotor of an induction motor is small, it can be measured by__
(a) Galvanometer
(b) D.C. moving coil milli-voltmeter
(c) D.C. moving coil ammeter
(d) A.C. voltmeter

3. The principal of operation of a 3-phase induction motor is most similar to that of a ___
(a) Synchronous motor
(b) Repulsion-start induction motor
(c) Transformer with a shorted secondary
(d) Capacitor-start induction-run motor

4. If the rotor of a 3-phase induction motor is assumed purely resistive, then electromagnetic torque is____
(a) minimum with load angle of 90 degree
(b) minimum with load angle of 0 degree
(c) optimum with load angle of 90 degree
(d) optimum with load angle of 90 degree

5. Which of the following motor has a squirrel-cage winding embedded in the armature under the regular winding?
(a) Compound motor
(b) Repulsion-start, induction-run motor
(c) Repulsion motor
(d) Repulsion-induction motor

6. For low and medium power derives, where speed control is not required, the motor that is recommended is____
(a) Synchronous motor
(b) Squirrel cage induction motor
(c) Double cage induction motor
(d) Three-phase series motor

7. A repulsion start induction-run motor runs as an induction motor when the
(a) commutator segments are short circuited
(b) brushes are shifted to a neutral plane
(c) shorting devices are disconnected
(d) stator connections are reversed

8. For a particular kW rating of an induction motor, the kVAR rating of the shunt capacitor required is _____.
(a) more for high rated speed motor
(b) more for lower rated speed motor
(c) independent of speed
(d) None of these

9. The induction motors develop which of the following at low frequency of the order 1/2 Hz to 10 Hz?
(a) High starting torque with excessive starting current
(b) High starting torque without excessive starting current
(c) Low starting torque with excessive starting current
(d) Low starting torque without excessive starting current

10. The primary reason for low power factor is owing to installation of ________
(a) synchronous motor
(b) dc motors
(c) induction motor
(d) None of these

Answers

    1. (d)    2. (b)    3. (c)    4. (d)    5. (d)
    6. (b)    7. (a)    8. (b)    9. (b)    10. (c)

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