Single Phase Motor Questions Answers

41. Cross-connecting of commutator bars in repulsion motors reduces circulating currents caused due to

(a) unequal air gaps between the stator and rotor.
(b) shorted stator winding.
(c) shorted brushes.
(d) all of these.

SHOW ANSWER

42. In repulsion motors, brush angle with respect to magnetic axis is kept

(a) 0° to 15°
(b) 15° to 45°
(c) 90°
(d) 180°

SHOW ANSWER

43. The torque-speed characteristic of a repulsion motor resembles which of the following dc motor characteristic ?

(a) Separately excited.
(b) Shunt.
(c) Series.
(d) Compound. [GATE E.E. 1996].

SHOW ANSWER

44. In a single-phase repulsion motor power factor is

(a) always leading.
(b) high at low speed.
(c) high at high speed.
(d) always unity. [A.M.I.E. Sec B. Elec. Machines Summer 1996]

SHOW ANSWER

45. In a repulsion motor by shifting the brush position

(a) speed and direction of rotation can be controlled.
(b) only speed can be controlled.
(c) speed, torque and direction of rotation can be controlled.
(d) only torque can be controlled by varying the speed at constant output power. [A.M.I.E. Sec B. Elec. Machines Winter 1996]

SHOW ANSWER

46. In a repulsion motor, if the angle of brush shift α from low impedance position is increased from 0 to 45° with constant current supply, then

(a) speed and power factor decrease but torque increases.
(b) speed and torque increase but pf decreases.
(c) speed, pf and torque increase.
(d) speed and pf increase but torque decreases. [A.M.I.E. Sec B. Summer 2002]

SHOW ANSWER

47. In a repulsion motor, torque developed will be zero when brush axis is at electrical degrees to the field axis.

(a) 0
(b) 90
(c) 45
(d) both(a) and (b)

SHOW ANSWER

48. In a repulsion motor speed control is affected by varying the

(a) impressed voltage.
(b) position of brushes.
(c) supply frequency.
(d) either (a) or (b).

SHOW ANSWER

49. Direction of rotation of a repulsion motor is reversed by.

(a) interchanging the supply leads.
(b) shifting the brushes round the commutator.
(c) either (a) or (b).
(d) none of these.

SHOW ANSWER

50. In a compensated repulsion motor, an additional stator winding is provided in order to

(a) improve power factor.
(b) provide better speed regulation.
(c) increase the output.
(d) improve mechanical balance.
(e) both (a) and (b).

SHOW ANSWER

51. A repulsion start induction motor operates as an induction motor when

(a) commutator segments are short circuited.
(b) brushes are short-circuited.
(c) stator is short-circuited.
(d) short-circuiting device is disconnected.

SHOW ANSWER

52. The short-circuiting device in a repulsion start induction motor operates by

(a) magnetic attraction.
(b) centrifugal force.
(c) circulating currents.
(d) none of the above.

SHOW ANSWER

53. The repulsion start induction motor has the advantage(s) of

(a) high starting torque (2.5 to 4.5 times of full-load torque).
(b) low starting current (about 3.5 times of full-load current).
(c) low cost, high efficiency and good power factor.
(d) both (a) and (b).

SHOW ANSWER

54. Which of the following statements regarding repulsion start induction motor is/are correct ?

(a) It runs below synchronous speeds on all loads.
(b) It needs more maintenance of commutator and other mechanical devices.
(c) It makes quite a bit noise on starting.
(d) It starts as a repulsion motor with its brushes set to give maximum torque.
(e) all of the above.

SHOW ANSWER

55. Repulsion induction motor has

(a) single phase winding on its stator.
(b) two separate windings on its rotor in common slots.
(c) squirrel cage rotor and two separate windings on stator in common slots.
(d) both (a) and (b).

SHOW ANSWER

56. In a repulsion induction motor, the rotor has a

(a) squirrel cage winding with rotor bars permanently short-circuited and placed at the bottom of the slots.
(b) repulsion winding similar to dc armature winding placed over the squirrel cage winding.
(c) repulsion winding placed at the bottom of slots and squirrel cage winding placed above the repulsion winding.
(d) both (a) and (b).

SHOW ANSWER

57. Which of the following statements regarding repulsion induction motor is wrong ?

(a) At start squirrel cage winding does not produce any torque.
(b) At start and at low speeds, major part of the torque is developed by repulsion winding.
(c) At rated load it almost runs at synchronous speed.
(d) It employs centrifugally operated mechanism for short-circuiting the commutator.

SHOW ANSWER

58. The repulsion induction motor has

(a) fairly good speed regulation.
(b) starting torque 2.25 to 3 times the full-load torque.
(c) starting current 3 to 4 times the full-load current.
(d) all of the above.

SHOW ANSWER

59. The repulsion induction motor does not have the drawback of

(a) higher cost.
(b) careful maintenance.
(c) poor starting torque.
(d) tendency of sparking.

SHOW ANSWER

60. Single phase synchronous motors

(a) are self starting motors.
(b) do not need dc excitation.
(c) operate at constant speed.
(d) are built for a wider range of output.
(e) all of the above.

SHOW ANSWER

Leave a Comment

Your email address will not be published. Required fields are marked *