Electrical Machine Design MCQ PDF Download

61. A machine is specified as 100 kW maximum continuous rating. The machine

(a) cannot be overloaded.
(b) can be overloaded by 10% only.
(c) can be overloaded by 20% only.
(d) can be overloaded by 25% for 2 hours only.

62. Short time rating machines have usually ………. operating time and …….. shutdown time.

(a) longer, longer
(b) smaller, smaller
(c) smaller, longer
(d) longer, smaller

63. The output of a rotating electrical machine is limited by

(a) peripheral velocity.
(b) temperature rise.
(c) size of machine.
(d) efficiency of the machine.

64. A shaft may fail due to fatigue developed due to

(a) stress concentration.
(b) presence of cyclic overloads.
(c) wrong adjustment of bearings, insufficient clearances etc.
(d) all of the above.

65. The desirable properties for the materials for the shafts are

(a) sufficient high strength.
(b) sensitivity to stress concentration.
(c) good machinability.
(d) ability to withstand heat and case hardening treatment to reduce the effects of stress concentration and increase the wear resistance of the journals.
(e) all of the above.

66. The design of shaft for an electrical machine is determined by considerations of

(a) ability to resist deflection due to weight of rotor and unbalanced magnetic pull.
(b) strength to transmit power.
(c) both (a) and (b).
(d) none of these.

67. Shaft is designed satisfying the requirements

(a) of sufficient strength to transmit torque at all loads without stress concentration.
(b) sufficiently rigid so that during operation the rotor does not touch the stator.
(c) critical speed of rotation must be different from the operating speeds of the machine.
(d) all of the above.

68. The shaft diameter in the bearings is usually …….. that under armature.

(a) 3/4 th of
(b) equal to
(c) 2/3 rd of
(d) 5/4 times of

69. The diameter of the shaft for a 500 V, 100 kW, 600 rpm motor is about

(a) 120 mm
(b) 60 mm
(c) 180 mm
(d) 240 mm

70. In ………. machines, the size (diameter) of the shaft is decided by the critical speed.

(a) small
(b) medium
(c) large
(d) any of these

71. The shaft of electric motors is generally supported in ………. bearings.

(a) magnetic
(b) ball of roller
(c) bush
(d) journal

72. The critical speed of the shaft for an electric motor should be ………. operating speed.

(a) exactly the same as
(b) away from the
(c) half of
(d) double of

73. Stiff shaft is necessary in case of induction motors due to

(a) small air gap.
(b) pulsating torque.
(c) high operating speed.
(d) all of the above.

74.……….. bearings are most commonly used in electrical machines up to rating of 500 kW.

(a) Ball and roller
(b) Thrust
(c) Both (a) and (b)
(d) none of these

75. Which of following bearings is/are classified as anti-friction bearings?

(a) Ball bearings.
(b) Roller bearings.
(c) Pedestal bearings.
(d) Shield bearings.
(e) Both ball and roller bearings.

76. Which of the following bearings are/is classified as sleeve bearings?

(a) Pedestal bearings.
(b) Shield bearings.
(c) Ball and roller bearings.
(d) Both pedestal and shied bearings.

77. Which of the following bearings is/are plain bearings?

(a) Pedestal bearings.
(b) Shield bearings.
(c) Ball bearings.
(d) Roller bearings.
(e) All of the above.

78. Bearings used for horizontal shaft machines are

(a) plain bearings.
(b) thrust bearings.
(c) either (a) or (b).
(d) none of these.

79. Bearings used for vertical shaft machines are

(a) plain bearings.
(b) thrust bearings.
(c) either (a) or (b).
(d) none of these.

80. Pedestal bearings are used for …….. machines.

(a) small size
(b) medium size
(c) large size
(d) medium and large size