Single Phase Motor Questions Answers

21. Two-value capacitor motor finds increased application as compressor motor in small home air-conditioners because

(a) it is comparatively cheaper.
(b) it has almost non-destructible capacitor.
(c) it has low starting as well as running currents at relatively high power factor.
(d) it is quiet in operation.

22. lf the centrifugal switch of a two-value capacitor motor using two capacitors fails to open then

(a) motor will not come up to speed
(b) motor will not carry the load
(c) current drawn by the motor will be excessively high
(d) electrolytic capacitor will in all probability, suffer break down

23. In a universal motor, the most common cause of brush sparking is

(a) open armature winding
(b) shorted armature winding
(c) shorted field winding
(d) high commutator mica
(e) all of the above

24. If starting winding of a single-phase induction motor is left in the circuit, it will

(a) run faster
(b) spark at light loads
(c) draw excessive current and over heat
(d) run slower

25. Most of the fractional horsepower motors have either

(a) hard and annealed bearings
(b) ball or roller bearings
(c) soft and porous bearings
(d) plain or sleeve bearings

26. Which of the following statements regarding reluctance-start motor is incorrect ?

(a) It is similar to reluctance motor.
(b) It is basically an induction motor and not a synchronous one.
(c) So far as its basic working principle is concerned, it is similar to shaded polo motor.
(d) The air-gap between rotor and salient poles is non- uniform.

27. To reverse the direction of rotation of a capacitor-start motor while it is running we should

(a) disconnect motor from the supply till it stops then reconnect it to supply with reversed connection of main or auxiliary winding
(b) disconnect motor from supply and immediately reconnect it to supply with reversed connections of the main winding
(c) reverse the direction of connection of the auxiliary winding and after motor comes to rest then connect auxiliary winding to the supply
(d) reverse the direction of connections of the auxiliary winding and immediately connect it to supply

28. When a ceiling fan employing a capacitor run motor is switched on it hums but does not burn. When it is driven by external means, it runs in whatever direction it is made to run. The trouble is due to

(a) blown fuse
(b) short in the capacitor
(c) an open in centrifugal switch
(d) an open in capacitor

29. Which of the following motors has two separate windings on the motor ?

(a) Repulsion motor
(b) Repulsion induction motor
(c) Repulsion start induction run motor
(d) None of the above

30. As hysteresis motors are free from mechanical and magnetic vibrations therefore these are considered as suitable for

(a) fans
(b) blowers
(c) sound equipment
(d) mixer grinders

31. Reluctance motors are

(a) singly excited
(b) doubly excited
(c) either of the above
(d) none of the above

32. Which motor will make least noise?

(a) Hysteresis motor
(b) Capacitor motor
(c) Shaded-pole motor
(d) Universal motor

33. Which motor is relatively free from mechanical and magnetic vibrations?

(a) Shaded-pole motor
(b) Universal motor
(c) Reluctance motor
(d) Hysteresis motor

34. A single-phase capacitor-start motor will take starting current nearly

(a) four to six times the full load current
(b) three times the full load current
(c) twice the full load current
(d) same as full load current

35. For a system involving sound recording and reproduction which motor would you select ?

(a) Shaded-pole motor
(b) Universal motor
(c) Reluctance motor
(d) Hysteresis motor

36. In a repulsion motor

(a) stator usually carries a distributed winding similar to the main winding of an ordinary single phase induction motor.
(b) the rotor or armature is similar to a dc motor armature with a drum type winding connected to the commutator.
(c) the brushes fixed directly opposite to each other are connected to each other or short-circuited.
(d) the speed is function of load
(e) all of the above.

37 The commutation of repulsion motor is at its best

(a) during starting.
(b) when runs near synchronous speed.
(c) when runs at 50% of synchronous speed.
(d) when runs at 150% of synchronous speed. [A.M.I.E. Sec B. Winter 2001]

38. Which of the following statements associated with repulsion motor is wrong ?

(a) Its direction of rotation depends upon the position of brushes.
(b) Its characteristics are similar to those of series motor.
(c) Its power factor is high.
(d) It is used where sturdy motor with large starting torque and adjustable but constant speed is required.

39. In a repulsion motor, commutator provides a means of connecting the

(a) stator windings.
(b) armature windings.
(c) starting winding.
(d) none of these.

40. In a repulsion motor the brushes are connected

(a) to the external supply.
(b) to each other or short-circuited.
(c) to the stator winding.
(d) none of the above.