MCQ Questions on Special Machines

26. Which of the following correctly defines the relationship between torque developed (T) and armature current (I) of a series motor? [UPRVUNL – 2014]

(a) T α I_a²
(b) T α I_a
(c) T α √I_a
(d) Tα l_a³

27. A single-phase preventer trips frequently in the motor. What is the reason for it

(a) Improper phase sequence
(b) Low supply voltage
(c) Abnormal fluctuation in the voltage
(d) Relay of single phase prevention is not energized

28. In a shaded pole motor the phase displacement occur by:

(a) Centrifugal switch
(b) Shading rings
(c) Capacitor
(d) Main pole winding [DMRC – 2015]

29. For which of the following pair of machines, the stator and its winding can be of the same type:

(a) Universal motor and stepper motor
(b) D.C. motor and hysteresis motor
(c) Hysteresis motor and reluctance motor
(d) Induction motor and D.C. motor [DMRC – 2014]

30. The range of efficiency for shaded pole motors is:

(a) 95% to 99%
(b) 80% to 90%
(c) 50% to 75%
(d) 5% to 35%

31. The speed of universal motor is generally reduced by:

(a) Gear trains
(b) V belts
(c) Brakes
(d) Chains [LMRC – 2015]

32. The starting winding of a single phase motor is placed in:

(a) Armature
(b) Field
(c) Rotor
(d) Stator

33. The rotor of which motor does not have winding on it?

(a) Repulsion motor
(b) universal motor
(c) Reluctance motor
(d) Hysteresis motor

34. A salient pole machine is used for

(a) Low speed applications in Hydro plants.
(b) High speed applications in Hydro plants.
(c) Low speed applications in Thermal plants.
(d) High speed application in Thermal plants.

35. The electric motor used in toys is

(a) Capacitor start motor
(b) Split phase motor
(c) Shaded pole motor
(d) None of these

36. A shaded pole induction motor does not have the advantage of

(a) Rugged construction
(b) Low initial as well as maintenance cost
(c) High starting torque
(d) Comparatively small starting current

37. Which type of motor is used for elevators?

(a) Synchronous motor
(b) Induction motor
(c) Split phase motor
(d) All of these

38. The rotor of a stepper motor has no

(a) Winding
(b) Commutator
(c) brushes
(d) All of the above [MPJE – 2015]

39. What is universal motor?

(a) Commutated DC series motor
(b) Homo polar DC motor
(c) Compensated DC motor
(d) Shunt DC motor

40. A split-phase motor is started by connecting both the running winding and starting winding across the line in

(a) Parallel
(b) Series
(c) Series-parallel
(d) An inductive coupling

41. A series motor must never be allowed to run at

(a) No load
(b) Full load
(c) Half load
(d) None of them

42. In repulsion motor, zero torque is developed when

(a) brush axis is 45 degree electrical to field axis
(b) brush axis is 90 degree electrical to field axis
(c) brush axis coincides with the field axis
(d) both (b) and (c)

43. The step angle of the stepper motor is 2.5°. If the stepping frequency is 3600 pulses per second, then the shaft speed will be

 (a) 144 rps
(b) 3600 rps
(c) 25 rps
(d) 2.5 rps

44. Which one of the following is not a fractional horse power motor? [UPSSSC – 2015]

(a) Shaded Pole motor
(b) Repulsion motor
(c) Universal motor
(d) Synchronous motor

45. The direction of rotation in a conventional shaded-pole motor can be reversed by

(a) Reversing the line connections
(b) Use of a capacitor
(c) Reversing the rotor
(d) Reversing the stator poles 180° [MPJE – 2016]

46. In a single phase ac motor, the condenser is used to

(a) Split the phase
(b) Minimise the radio interference
(c) Minimise the losses
(d) Minimise the current [MPJE 2016]

47. Which of the following is common cause of brush sparking in a universal motor? [MPJE – 2016]

(a) Single phase armature winding
(b) Open armature winding
(c) High commutator mica
(d) Shorted armature winding, open armature winding and high commutator mica

48. Which of the following motor does not use a centrifugal switch? [MPJE – 2016]

(a) Single phase induction motor
(b) Capacitor start capacitor run motor
(c) Shaded pole motor
(d) None of these

49. Universal motor is used in sewing machines. It’s speed is controlled by

(a) Field tapping
(b) Friction
(c) Field diversion
(d) Varying resistance [UPPCL – 2016]