MCQ of Electrical Machines page-4

61. The equalizer rings are used in

Lap winding.
(b) Wave winding.
(c) Multilayer wave winding.
(d) None of the above.

62.The generator is called flat compounded if

The series field ampere turns are such as to produce the same voltage at rated load as at no load.
(b) The series field turns are such as that the rated load voltage is greater than no load voltage.
(c) The rated voltage is less than the no load voltage.
(d) None of the above.

63. The slip test is used

(a) To measure the slip of the induction motor.
(b) To measure the torque of the induction motor.
To measure the X_d and X_q of the alternator.
(d) For none of the above.

64. What will happen if the back e.m.f. in the d.c. motor absent ?

(a) Motor will run faster than rated value.
Motor will burn.
(c) Armature drop will be reduced substantially.
(d) None of the above.

65. The armature torque of the d.c. shunt motor is proportional to

Armature current only.
(b) Field flux only.
(c) Armature current and flux both.
(d) None of the above.

66. The back e.m.f. has no relation with armature torque in d.c. motor.

(a) true.
false.

67. The speed of the d.c shunt motor increases as the armature torque increases.

(a) true.
false.

68. The horsepower obtained from the shaft torque is called

(a) Indicated horsepower or I.H.P.
Brake horsepower or B.H.P.
(c) F.H.P.
(d) None of the above.

69. For d.c. shunt motors the speed is dependent on back e.m.f, only because

Flux is practically constant in d.c shunt motor.
(b) Flux is proportional to armature current.
(c) Armature drop is negligible.
(d) Back e.m.f. is equal to armature drop .

70.It is preferable to start d.c. series motor with some mechanical load because

It may develop excessive speed otherwise and damage itself.
(b) It will not run at no load .
(c) A little load will act as a starter to the motor.
(d) None of the above.

71. When the torque of the d.c. series motor is doubled the power is increased by

(a) 70% .
50% to 60% .
(c) 20% .
(d) 100%.

72. When two d.c. series generators are running in parallel an equalizer bar is used

Because two similar machines will pass approximately equal currents to the load.
(b) To reduce the combined effect of armature reaction of both machines.
(c) To increase the speed and hence generated e.m.f..
(d) To increase the series flux.

73. The speed of the d.c. motor can be controlled by

(a) Controlling flux only.
Controlling flux, armature resistance and voltage.
(c) Controlling voltage and flux only.
(d) Controlling armature resistance and voltage only.

74. The diverter in d.c. machine is basically potential divider.

(a) true.
false.

75. The speed/current curve for a d.c. series motor with resistance in series field will lie above the curve without resistance in series field.

(a) true.
false.

76. A diverter across the armature of d.c. motor cannot be used for giving speed lower than the rated speed

a) true.
false.

77. the field flux of the d.c. motor can be controlled to achieve.

The speeds above the rated speed.
(b) The speeds lower than rated speed.
(c) The speeds above and below the rated speed.
(d) Steady speed.

78. The reversal of rotation of motors and as electric braking is known as

(a) regenerative braking .
plugging.
(c) dynamic braking .
(d) none of the above.

79. Which of the following methods of braking is used in rolling mills?

plugging .
(b) regenerative braking.
(c) dynamic braking.
(d) mechanical brakes.

80. Regenerative method of braking is based on that

Back e.m.f. of motor is more than the applied voltage.
(b) Back e.m.f. is equal to the applied voltage.
(c) Back e.m.f is less than the applied voltage.
(d) None of the above.

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