Single Phase Induction Motor MCQ

21. The power factor at which single phase induction motors usually operate is

(a) 0.7 lag.
(b) 0.8 lag.
(c) 0.7 lead.
(d) unity.

22. Which of the following tests are performed on single phase ac motors ?

(a) Stator winding resistance test.
(b) Blocked rotor test.
(c) No-load test.
(d) All of the above.

23. Single phase induction motors are made self starting by

(a) increasing rotor resistance.
(b) using an external starting device.
(c) providing an additional winding on the stator called the auxiliary winding.
(d) any of the above methods.

24. The two windings provided on the stator of a single phase induction motor, one main winding and the other auxiliary winding are connected

(a) in parallel.
(b) in series.
(c) either in series or in parallel depending on the design of the motor.
(d) through inductive coupling.

25. The stator winding of a single phase induction motor is splitted into two parts in order to

(a) improve efficiency.
(b) improve power factor.
(c) develop starting torque.
(d) increase speed.

26. In a single phase induction motor

(a) both the main and auxiliary windings are placed on stator.
(b) both the main and auxiliary windings are placed on rotor.
(c) main winding is placed on stator and auxiliary winding on rotor.
(d) auxiliary winding is placed on stator and main winding on rotor.

27. Phase splitting can be accomplished in a single phase induction motor

(a) only by adding a capacitor in series with the auxiliary winding.
(b) only by causing the auxiliary winding to have high reactance.
(c) only by causing the auxiliary winding to have low resistance.
(d) by any one of the above three methods. [A.M.I.E. Sec B. Elec. Machines Winter 1994]

28. Which of the following statements associated with split-phase motors is incorrect ?

(a) Auxiliary winding is wound of fine wire and is placed in the top of the slots to give high resistance and low reactance.
(b) Main winding has low resistance and high reactance.
(c) Main winding current and auxiliary winding current are 90° out of phase.
(d) Torque developed is proportional to sine of the angle between main winding and auxiliary winding currents.
(e) Starting winding is connected through centrifugal switch.

29. In a split-phase motor the ratio of number of turns on auxiliary winding to that on main winding is

(a) unity.
(b) less than one.
(c) more than one.
(d) two.

30. Why is a centrifugal switch used in a single-phase induction motor?

(a) To protect the motor from overloading.
(b) To improve the starting performance of the motor.
(c) To cut off the starting winding at an appropriate instant.
(d) To cut in the capacitor during running conditions. [IES. E.E.-11, 2008]

31. Centrifugal switch fitted on the rotor will operate when

(a) rotor speed reaches its rated condition.
(b) rotor speed exceeds 70 per cent of its rated value.
(c) rotor speed exceeds synchronous speed.
(d) rotor speed exceeds 40 per cent of its rated value.

32. The torque-speed characteristic of two phase induction motor is largely affected by

(a) voltage.
(b) speed.
(c) X/R ratio.
(d) supply frequency.

33. Which of the following statement(s) about split-phase motors is/ are correct ?

(a) Its starting torque is 1.5 to 2 times of full-load running torque.
(b) Its starting current is about 7 times of full-load current.
(c) Main winding and auxiliary winding currents are about 30° out of phase.
(d) all of the above.

34. The direction of rotation of a split-phase induction motor can be reversed by reversing the connections to the supply of

(a) auxiliary winding only.
(b) main winding only.
(c) either (a) or (b).
(d) both (a) and (b) simultaneously.

35. The capacitor in a capacitor-start induction run ac motor is connected in series with

(a) starting winding.
(b) main winding
(c) squirrel cage winding.
(d) compensating winding.

36. A single phase induction motor is provided with a 3-phase slip-ring rotor connected to starting resistances. The motor would

(a) not start.
(b) result in more starting torque.
(c) produce no difference in the starting torque.
(d) run at half the synchronous speed. [A.M.I.E. Sec B. Winter 2003]

37. In a single phase induction motor driving a fan load, the reason for having a high resistance rotor is to achieve

(a) low starting torque.
(b) quick acceleration.
(c) high efficiency.
(d) reduced size. [GATE E.E. 2005]

38. Capacitor in a single-phase induction motor is used for

(a) improving the power factor.
(b) improving the starting torque.
(c) starting the motor.
(d) reducing the harmonics. [I.E.S. E.E-II, 2002]

39. 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. [GATE E.E. 2006]

40. The capacitor usually used on 1440 rpm, 50 Hz capacitor-start induction motor is of electrolytic type and ……… capacity.

(a) 10 µF
(b) 100 µF
(c) 350 µF
(d) 800 µF