1. A transformer can have regulation closer to zero
Correct : C. on leading power factor
2. A transformer transforms
Correct : D. power
3. Which of the following is not the standard voltage for power supply in India ?
Correct : D. 122 kV
4. Reduction in core losses and increase in permeability are obtained with transformer
employing
Correct : A. core built-up of laminations of cold rolled grain oriented steel
5. In a power or distribution transformer about 10 per cent end turns are heavily insulated
Correct : A. to withstand the high voltage drop due to line surge produced by the shunting capacitance of the end turns
6. For given applied voltage, with the increase in frequency of the applied voltage
Correct : C. eddy current loss will remain unchanged
7. Losses which occur in rotating electric machines and do not occur in transformers are
Correct : A. friction and windage losses
8. In a given transformer for a given applied voltage, losses which remainconstant
irrespective of load changes are
Correct : A. hysteresis and eddy current losses
9. Which of the following statements regarding an idel single-phase transformerhaving a
turn ratio of 1 : 2 and drawing a current of 10 A from 200 V A.C. supply is incorrect ?
Correct : D. Its secondary current is 20 A
10. The secondary of a current transformer is always short-circuited underoperating
conditions because it
Correct : A. avoids core saturation and high voltage induction
11. In a transformer the resistance between its primary and secondary should be
Correct : D. infinity
12. A good voltage regulation of a transformer means
Correct : A. output voltage fluctuation from no load to full load is least
13. For a transformer, operating at constant load current, maximum efficiency will occur at
Correct : D. unity power factor
14. Which of the following protection is normally not provided on smalldistribution
transformers ?
Correct : B. Buchholz relay
15. Which of the following acts as a protection against high voltage surges due to
lightning and switching ?
Correct : A. Horn gaps
16. The efficiency of two identical transformers under load conditionscan be
determined by
Correct : B. back-to-back test
17. Which of the following insulating materials can withstand the highest temperature
safely ?
Correct : C. Mica
18. Which of the following parts of a transformer is visible from outside ?
Correct : A. Bushings
19. The noise produced by a transformer is termed as
Correct : B. hum
20. Which of the following loss in a transformer is zero even at full load ?
Correct : B. Friction loss
21. Which of the following is the most likely source of harmonics in a transformer ?
Correct : D. Core saturation
22. If a transformer is continuously operated the maximum temperature rise will occur in
Correct : B. windings
23. The hum in a transformer is mainly attributed to
Correct : C. magnetostriction
24. The maximum load that a power transformer can carry is limited by its
Correct : C. voltage ratio
25. The efficiency of a transformer, under heavy loads, is comparatively low because
Correct : A. copper loss becomes high in proportion to the output
26. An open-circuit test on a transformer is conducted primarily to measure
Correct : C. core loss
27. A no-load test is performed on a transformer to determine
Correct : D. magnetising current and loss
28. The voltage transformation ratio of a transformer is equal to the ratio of
Correct : C. secondary induced e.m.f. to primary induced e.m.f.
29. Part of the transformer which is most subject to damage from overheating is
Correct : C. winding insulation
30. If a transformer is switched on to a voltage more than the rated voltage
Correct : A. its power factor will deteriorate
31. Auto-transformer makes effective saving on copper and copper losses, whenits
transformation ratio is
Correct : A. approximately equal to one
32. Minimum voltage regulation occurs when the power factor of the load is
Correct : C. leading
33. In a step-down transformer, there is a change of 15 A in the load current. This results in
change of supply current of
Correct : A. less than 15 A
34. No-load speed of which of the following motor will be highest ?
Correct : B. Series motor
35. The direction of rotation of a D.C. series motor can be changed by
Correct : B. interchanging field terminals
36. Which of the following application requires high starting torque ?
Correct : C. Locomotive
37. If a D.C. motor is to be selected for conveyors, which rriotor would be preferred ?
Correct : A. Series motor
38. Which D.C. motor will be preferred for machine tools ?
Correct : B. Shunt motor
39. Differentially compound D.C. motors can find applicationsrequiring
Correct : B. low starting torque
40. Which D.C. motor is preferred for elevators ?
Correct : D. Cumulative compound motor
41. If the field of a D.C. shunt motor gets opened while motor is running
Correct : C. the motor will attain dangerously high speed 1
42. Starters are used with D.C. motors because
Correct : D. to restrict armature current as there is no back e.m.f. whilestarting
43. In D.C. shunt motors as load is reduced
Correct : C. the speed will remain almost/constant
44. A D.C. series motor is that which
Correct : A. has its field winding consisting of thick wire and lessturns
45. For starting a D.C. motor a starter is required because
Correct : B. it limits the starting current to a safe value
46. The type of D.C. motor used for shears and punches is
Correct : D. cumulative compound D.C. motor
47. If a D.C. motor is connected across the A.C. supply it will
Correct : D. burn due to heat produced in the field winding by .eddy currents
48. To get the speed of D.C, motor below the normal without wastage of electrical energy is
used.
Correct : A. Ward Leonard control
49. When two D.C. series motors are connected in parallel, the resultant speed is
Correct : C. normal speed
50. The speed of a D.C. shunt motor more than its full-load speed can be obtained by
Correct : A. decreasing the field current
51. In a D.C. shunt motor, speed is
Correct : A. independent of armature current
52. A direct on line starter is used: for starting motors
Correct : A. iip to 5 H.P.
53. What will happen if the back e.m.f. of a D.C. motor vanishes suddenly?
Correct : C. The armature may burn
54. In case of D.C. shunt motors the speed is dependent on back e.m.f. only because
Correct : D. flux is practically constant in D:C. shuntmotors
55. In a D.C. shunt motor, under the conditions of maximum power, the current inthe
armature will be
Correct : D. more than full-load current
56. These days D.C. motors are widely used in
Correct : C. electric traction
57. By looking at which part of the motor, it can be easily confirmedthat a particular
motor is D.C. motor?
Correct : C. Commutator
58. In which of the following applications D.C. series motor is invariably tried?
Correct : A. Starter for a car
59. In D.C. machines fractional pitch winding is used
Correct : D. to reduce the sparking
60. A three point starter is considered suitable for
Correct : B. shunt as well as compound motors
61. In case-the conditions for maximum power for a D.C. motor are established,the
efficiency of the motor will be
Correct : D. less than 50%
62. The ratio of starting torque to full-load torque is least in case of
Correct : B. shunt motors
63. In D.C. motor which of the following can sustain the maximum temperature rise?
Correct : C. Field winding
64. Which of the following law/rule can he used to determine the direction of rotationof
D.C. motor ?
Correct : D. Fleming's left-hand rule
65. Which of the following load normally needs starting torque more than therated
torque?
Correct : B. Conveyors
66. The starting resistance of a D.C. motor is generally
Correct : A. low
67. The speed of a D.C. series motor is
Correct : D. inversely proportional to the armature current
68. In a D.C. series motor, if the armature current is reduced by 50%, the torque of the
motor will be equal to
Correct : C. 25% of the previous value
69. The current drawn by the armature of D.C. motor is directly proportional to
Correct : A. the torque required
70. The power mentioned on the name plate of an electric motor indicates
Correct : D. the output power available at the shaft
71. Which D.C. motor has got maximum self loading property?
Correct : D. Differentially compounded motor
72. Which D.C. motor will be suitable alongwith flywheel for intermittent light andheavy
loads?
Correct : C. Cumulatively compounded motor
73. If a D.C. shunt motor is working at no load and if shunt field circuit suddenly opens
Correct : C. this will result in excessive speed, possibly destroying armature due to excessive centrifugal stresses
74. D.C. series motors are used
Correct : D. in none of the above situations.
75. For the same H.P. rating and full load speed, following motor has poor starting torque
Correct : C. differentially compounded
76. In case of conductively compensated D.C. series motors, the compensating winding is provided
Correct : C. in series with armature winding
77. Sparking at the commutator of a D.C. motor may result in
Correct : D. all of the above
78. Which of the following motor is preferred for operation in highly explosive
atmosphere ?
Correct : C. Air motor
79. If the supply voltage for a D.C. motor is increased, which of the following willdecrease
?
Correct : C. Full-load current
80. Which one of the following is not the function of pole shoes in a D.C. machine ?
Correct : A. To reduce eddy current loss
81. The mechanical power developed by a shunt motor will be maximum when theratio of
back e.m.f. to applied voltage is
Correct : D. 0.5
82. For which of the following applications a D.C. motor is preferred over an A.C. motor?
Correct : C. Variable speed operation
83. In D.C. machines the residual magnetism is of the order of
Correct : A. 2 to 3 per cent
84. Which D.C. motor is generally preferred for cranes and hoists ?
Correct : A. Series motor
85. Three point starter can be used for
Correct : D. both shunt and compound motor
86. Sparking, is discouraged in a D.C. motor because
Correct : B. commutator gets damaged
87. Speed control by Ward Leonard method gives uniform speed variation
Correct : B. in both directions
88. Flywheel is used with D.C. compound motor to reduce the peak demand by the motor,
compound motor will have to be
Correct : C. cumulatively compounded
89. Following motor is used where high starting torque and wide speed range control is required.
Correct : D. D.C. motor
90. In a differentially compounded D.C. motor, if shunt field suddenly opens
Correct : A. the motor will first stop and then run in opposite direction as series motor
91. Which of the following motor has the poorest speed regulation ?
Correct : B. Series motor
92. Buses, trains, trolleys, hoists, cranes require high starting torque and therefore make use
of
Correct : A. D.C. series motor
93. As -the load is increased the speed of D.C. shunt motor will
Correct : A. reduce slightly
94. The armature torque of the D.C. shunt motor is proportional to
Correct : B. armature current only
95. Which of the following method of speed control of D.C. machine will offer minimum
efficiency ?
Correct : C. Armature control method
96. Usually wide and sensitive speed control is desired in case of
Correct : D. colliery winders
97. The speed of a motor falls from 1100 r.p.m. at no-load to 1050 r.p.m. at rated load.The speed regulation of the motor is
Correct : B. 4.76%
98. The armature voltage control of D.C. motor provides
Correct : A. constant torque drive
99. As there is no back e.m.f. at the instant of starting a D.C. motor, in order to prevent a
heavy current from flowing though the armature circuit
Correct : A. a resistance is connected in series with armature
100. The speed of a D.C. shunt motor can be increased by
Correct : B. increasing the resistance in field circuit