61. A dc shunt generator driven at a normal speed in the normal direction fails to build up armature voltage because
a) the resistance of the armature is high
b) there is no residual magnetism
c) the field current is too small
d) none of these
ans. b
62. An ideal dc generator has a regulation of
a) 0%
b) 50%
c) 75%
d) 100%
ans. a
63. Which of the following statements is incorrect in dc shunt generators about hysteresis loss?
a) It can be minimized by laminating the armature
b) It is independent of lamination thickness
c) It depends upon the supply frequency
d) none of these
ans. a
64. Which of the following methods is most economical for finding the no-load losses of a large dc shunt motor?
a) Hopkinson's test
b) Swinburne's test
c) Retardation test
d) none of these
ans. b
65. The rated speed of a given dc shunt motor is 1050 rpm.To run this machine at 1200rpm , which of the following speed control scheme will be used
a) Armature current resistance control
b) Field resistance control
c) Ward-Leonard control
d) none of these
ans. b
66. The destroyed residual magnetism of a shunt generator may restored by connecting its shunt field to
a) earth
b) generator
c) a battery
d) none of these
ans. d
67. It is preferable to start a dc series motor with some mechanical load on it because
a) it will not run at no load
b) it acts as a starter to the motor
c) it may develop excessive speed and damage itself
d) none of these
ans. c
68. If the flux of a dc motor approaches zero, its speed will approach
a) infinity
b) zero
c) a stable value nearer to the rated speed
d) none of these
ans. a
69. As the load is increased, speed of a shunt motor
a) remains constant
b) increases slightly
c) reduces slightly
d) none of these
ans. c
70. A 230 V dc series motor is connected to 230 V ac it will
a) run slowly
b) not run at all
c) run with less efficiency
d) none of these
ans. c
a) the resistance of the armature is high
b) there is no residual magnetism
c) the field current is too small
d) none of these
ans. b
62. An ideal dc generator has a regulation of
a) 0%
b) 50%
c) 75%
d) 100%
ans. a
63. Which of the following statements is incorrect in dc shunt generators about hysteresis loss?
a) It can be minimized by laminating the armature
b) It is independent of lamination thickness
c) It depends upon the supply frequency
d) none of these
ans. a
64. Which of the following methods is most economical for finding the no-load losses of a large dc shunt motor?
a) Hopkinson's test
b) Swinburne's test
c) Retardation test
d) none of these
ans. b
65. The rated speed of a given dc shunt motor is 1050 rpm.To run this machine at 1200rpm , which of the following speed control scheme will be used
a) Armature current resistance control
b) Field resistance control
c) Ward-Leonard control
d) none of these
ans. b
66. The destroyed residual magnetism of a shunt generator may restored by connecting its shunt field to
a) earth
b) generator
c) a battery
d) none of these
ans. d
67. It is preferable to start a dc series motor with some mechanical load on it because
a) it will not run at no load
b) it acts as a starter to the motor
c) it may develop excessive speed and damage itself
d) none of these
ans. c
68. If the flux of a dc motor approaches zero, its speed will approach
a) infinity
b) zero
c) a stable value nearer to the rated speed
d) none of these
ans. a
69. As the load is increased, speed of a shunt motor
a) remains constant
b) increases slightly
c) reduces slightly
d) none of these
ans. c
70. A 230 V dc series motor is connected to 230 V ac it will
a) run slowly
b) not run at all
c) run with less efficiency
d) none of these
ans. c
