Electrical Machines - Induction Motors

Following questions are taken from SSC J.E. 2018 Exam from different sets

1.In three induction motor maximum torque is inversely proportional to the
(a) stator voltage 
(b) speed of rotor
(c) rotor reactance
(d) decreasing slip speed
Hint: {T_{\max }} = \frac{{3{V^2}}}{{{\omega _s}^2{X_2}}}

2. No-load test on induction motor is conducted to find which of the following losses?
(a) stator core loss 
(b) rotational loss
(c) Stator copper loss 
(d) All options are correct

3. A single-phase induction motor with only the main winding excited would exhibit the following response at synchronous speed
(a) Rotor current is zero
(b) Rotor current is non-zero and is at slip frequency
(c) Forward and backward rotating fields are equal
(d) Forward rotating field is more than the backward rotating field

4. In squirrel cage induction, the rotor slots are slight skew in order to reduce
(a) windage losses
(b) eddy currents
(c) reduce magnetic humming effect
(d) friction losses

5. For a single phase capacitor start induction motor which of the following statements is valid?
(a) The capacitor is used for power factor improvement
(b) The direction of rotation can be changed by reversing the main winding terminals
(c) The direction of rotation cannot be changed
(d) The direction of rotation can be changed by interchanging the supply terminals

6. The capacity of Single phase induction motor is limited by
(a) Pulsating torque
(b) uniform torque
(c) non uniform torque
(d) None of these

7. Rotating magnetic fields are also used in 3 phase induction motors rotor developing____.
(a) eddy current
(b) voltage lag
(c) load current 
(d) phase current

8. One of the speed control methods of a 3 phase induction motors is___.
(a) V/F control
(b) stator current control
(c) core loss control 
(d) eddy current control

9. If the air gap in an induction motor is increased _____.
(a) speed of rotor increases
(b) the power factor will decrease
(c) the windage losses will increase
(d) current drawn by the motor increase

10. In three phase induction motor reversing the supply in two of the phases is called as______.
(a) pole changing
(b) plugging
(c) Increase the torque
(d) to control current

Answers

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

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