1. Explain the principle of working of a three-phase induction motor.
2. Explain why a three-phase induction motor can not run at synchronous speed.
3. What is meant by slip in an induction motor? What will be the value of slip at starting
and at synchronous speed?
4. Is it possible to change the direction of rotation of three phase induction motors? How?
5. Explain the purpose of making two types of rotor construction for three-phase induction
motors.
6. Derive an expression for the torque developed in an induction motor.
7. Draw the torque-speed characteristic of a three-phase induction motor and explain its
shape. Explain the effect of cogging and crawling on its shape.
8. Show that stator magnetic field and the field produced by the rotor mmf are stationary
with respect to each other.
9. Differentiate between slip ring and squirrel cage induction motors
10. Explain why the slots of a double cage induction motors have narrow constriction
between the space for placing top and bottom bars.
11. Draw and explain the phasor diagram of a three phase induction motor.
12. Draw the power flow diagram of a three phase induction motor and hence derive the
relationship between rotor output, rotor input and slip.
13. With a neat speed characteristics explain the modes of operation of three phase induction
motor.
14. List the applications of squirrel cage and slip ring induction motors.
15. List the different methods of speed control of three phase induction motors. Explain them
in brief.
16. Show that the maximum torque of a three phase induction motor is independent of rotor
resistance but the slip at which the maximum torque occurs is dependent on rotor
resistance.
17. Sketch the torque slip characteristics of a three phase induction motor and explain clearly
the following: (a) starting torque (b) pull out torque (c) Load torque (d) maximum torque
(e) stable and unstable regions of operation. Show the regions on the characteristics.
18. Draw the torque slip characteristics of a three phase induction motor and show three
major regions of operation.
19. Draw the torque slip characteristics of single cage, double cage, and deep bar induction
motor and comment on the shapes with respect to their rotor construction.
20. With neat circuit diagram explain the no load and blocked rotor test to be conducted on
three phase induction motor. Explain how the equivalent circuit parameters can be
obtained from the test results.
21. Deduce the parameters of the equivalent circuit of a three phase induction motor
considering the rotor to be star connected with N2 turns per phase. Draw the equivalent
circuit and insert all the parameters.
22. Explain the need for starters for three phase induction motors. With a neat circuit diagram
explain star delta starting of three phase induction motor.
23. Explain the constructional features of a double cage three phase induction motor.
24. Draw the torque speed characteristics of an induction motor when its speed is controlled
by (i) voltage control (ii) rotor resistance control (iii) voltage frequency (v/f) control.
25. State the effect of increasing rotor resistance on starting current, maximum torque and
full load slip of an induction motor.
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26. Explain how a three phase induction motor can work as a induction generator. Mention
the practical application of this method.
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