Electrical Drives MCQs

61. Which of the following motors has series characteristics?

(a) Shaded pole motor
(b) Repulsion motor
(c) Capacitor start motor
(d) None of the above

Answer. b

62. Which of the following happens when a star-delta starter is used?

(a) Starting voltage is reduced
(b) Starting current is reduced
(c) Both (a) and (b)
(d) None of the above

Answer. c

63. For a D.C. shunt motor which of the following is incorrect?

(a) Unsuitable for heavy duty starting
(b) Torque varies as armature current
(c) Torque-armature current is a straight line
(d) Torque is zero for zero armature current

Answer. a

64. For which of the following applications motor has to start with high acceleration?

(a) Oil expeller
(b) Floor Mill
(c) Lifts and hoists
(d) Centrifugal pump

Answer. c

65. Which of the following types of the motor enclosure is safest?

(a) Totally enclosed
(b) Totally enclosed fan cooled
(c) Open type
(d) Semi closed

Answer. b

66. While selecting a motor for an air conditioner which of the following characteristics is of great importance?

(a) Type of bearings
(b) Type of enclosure
(c) Noise
(d) Arrangement for power transmission.
(e) None of the above

Answer. c

67. The diameter of the rotor shaft for an electric motor depends on which of the following?

(a) r.p.m only
(b) Horse power only
(c) Horse power and r.p.m.
(d) Horse power, r.p.m. and power factor

Answer. c

68. Which of the following alternatives will be cheaper?

(a) A 100 H.P. A.C. three phase motor
(b) Four motors of 25 H.P. each
(c) Five motors of 20 H.P. each
(d) Ten motors of 10 H.P. each

Answer. a

69. The cost of an induction motor will increase as

(a) horsepower rating increases but r.p.m. decreases
(b) horsepower rating decreases but r.p.m. increases
(c) horsepower rating and operating speed increases
(d) horsepower rating and operating speed decreases

Answer. a

70. In series motor which of the following methods can be used for changing the flux per pole?

(a) Tapped field control
(b) Diverter field control
(c) Series-parallel control
(d) Any of the above

Answer. d