21. For induction motors normally
- The stator winding is connected to ac supply and the rotor winding is short circuited
- The rotor winding is connected to ac supply and the stator winding is short circuited.
- Both the stator and rotor windings are connected to ac supply
- Stator winding is connected to ac supply and rotor winding to dc supply
22. A 3- phase, 4-pole squirrel cage induction motor has 36 stator and 28 rotor slots. The number of phases in the rotor is
- 3
- 9
- 7
- 8
23. The rotor slots are slightly skewed in squirrel – cage induction motor to
- increase the strength of rotor bars
- reduce the magnetic hum and locking tendency of rotor
- economize on the copper to be used
- provide ease of fabrication
24. The principle of operation of a 3-phase induction motor is almost similar to that of
- Synchronous motor
- Repulsion start induction motor
- Transformer with a shorted secondary
- Capacitor-start induction motor
25. The rotor of the 3- phase induction motor rotates in the same direction as that of stator rotating field. This can be explained by
- Faraday’s law of electromagnetic induction
- Lenz’s law
- Newton’s laws of motion
- Fleming’s right hand rule
26. The relative speed between stator and rotor fluxes is equal to
- Synchronous speed, Ns
- Rotor speed, N
- Zero
- Ns – N
27. Stator flux induces emf in the rotor bars
- Rotating at synchronous speed around stator
- Constant in magnitude
- Magnitude depending upon the load on the motor
- None of the above
28. The rotor circuit of an induction motor under operating condition is
- Always closed
- Always open
- May be open and closed depending upon the loading conditions
29. The 3- phase induction motor with rotor circuit open will
- Run normally
- Get overheated
- Not run
- Make noise
30. If any two leads from slip rings are interchanged in a 3- phase induction motor, the motor will
- Continue running in the same direction as before
- Run in a direction opposite to previous one
- Not run
- Get damaged