MCQs on transformer 121-140

121. Which of the following loss in a transformer is zero even at full load ?
(a) Core loss
(b) Friction loss✔
(c) Eddy current loss
(d) Hysteresis loss

122. Which of the following is the most likely source of harmonics in a transformer ?
(a) poor insulation
(b) Overload
(c) loose connections
(d) Core saturation✔

123. If a transformer is continuously operated the maximum temperature rise will occur in
(a) core
(b) windings✔
(c) tank
(d) any of the above

124. The hum in a transformer is mainly attributed to
(a) load changes
(b) oil in the transformer
(c) magnetostriction✔
(d) mechanical vibrations

125. The maximum load that a power transformer can carry is limited by its
(a) temperature rise
(b) dielectric strength of oil
(c) voltage ratio✔
(d) copper loss

126. The efficiency of a transformer, under heavy loads, is comparatively low because
(a) copper loss becomes high in proportion to the output✔
(b) iron loss is increased considerably
(c) voltage drop both in primary and secondary becomes large
(d) secondary output is much less as compared to primary input

127. An open-circuit test on a transformer is conducted primarily to measure
(a) insulation resistance
(b) copper loss
(c) core loss✔
(d) total loss

128. A no-load test is performed on a transformer to determine
(a) core loss
(b) copper loss
(c) efficiency
(d) magnetising current and loss✔

129. The voltage transformation ratio of a transformer is equal to the ratio of
(a) primary turns to secondary turns
(b) secondary current to primary current
(c) secondary induced e.m.f. to primary induced e.m.f.✔
(d) secondary terminal voltage to primary applied voltage

130. Part of the transformer which is most subject to damage from overheating is
(a) iron core
(b) copper winding
(c) winding insulation✔
(d) frame or case

136. If a transformer is switched on to a voltage more than the rated voltage
(a) its power factor will deteriorate✔
(b) its power factor will increase
(c) its power factor will remain unaffected
(d) its power factor will be zero

137. Auto-transformer makes effective saving on copper and copper losses, when its transformation ratio is
(a) approximately equal to one✔
(b) less than one
(c) great than one
(d) none of the above

138. Minimum voltage regulation occurs when the power factor of the load is
(a) unity
(b) lagging
(c) leading
(d) zero✔

139. In a step-down transformer, there is a change of 15 A in the load current. This results in change of supply current of
(a) less than 15 A✔
(b) more than 15 A
(c) 15 A
(d) none of the above

140. The efficiencies of transformers compared with that of electric motors of the same power are
(a) about the same
(6) much smaller
(c) much higher✔
(d) somewhat smaller

MCQs on Transformer 101-120

101. A shell-type transformer has
(a) high eddy current losses
(b) reduced magnetic leakage✔
(c) negligibly hysteresis losses
(d) none of the above

102. A transformer can have regulation closer to zero
(a) on full-load
(b) on overload
(c) on leading power factor✔
(d) on zero power factor

103. A transformer transforms
(a) voltage
(b) current
(c) current and voltage
(d) power✔

104. Which of the following is not the standard voltage for power supply in India ?
(a) llkV
(b) 33kV
(c) 66 kV
(d) 122 kV✔

105. Reduction in core losses and increase in permeability are obtained with transformer employing
(a) core built-up of laminations of cold rolled grain oriented steel✔
(b) core built-up of laminations of hot rolled sheet
(c) either of the above
(d) none of the above

106. In a power or distribution transformer about 10 per cent end turns are heavily insulated
(a) to withstand the high voltage drop due to line surge produced by the shunting capacitance of the end turns✔
(b) to absorb the line surge voltage and save the winding of transformer from damage
(c) to reflect the line surge and save the winding of a transformer from damage
(d) none of the above

107. For given applied voltage, with the increase in frequency of the applied voltage
(a) eddy current loss will decrease
(b) eddy current loss will increase
(c) eddy current loss will remain unchanged✔
(d) none of the above

108. Losses which occur in rotating electric machines and do not occur in trans formers are
(a) friction and windage losses✔
(b) magnetic losses
(c) hysteresis and eddy current losses
(d) copper losses

109. In a given transformer for a given applied voltage, losses which remain constant irrespective of load changes are
(a) hysteresis and eddy current losses✔
(b) friction and windage losses
(c) copper losses
(d) none of the above

110. Which of the following statements regarding an idel single-phase transformer having a turn ratio of 1 : 2 and drawing a current of 10 A from 200 V A.C. supply is incorrect ?
(a) Its secondary current is 5 A
(b) Its secondary voltage is 400 V
(c) Its rating is 2 kVA
(d) Its secondary current is 20 A✔

111. The secondary of a current transformer is always short-circuited under operating conditions because it
(a) avoids core saturation and high voltage induction✔
(b) is safe to human beings
(c) protects the primary circuit
(d) none of the above

112. In a transformer the resistance between its primary and secondary should be
(a) zero
(b) 10 Q
(c) 1000 Q
(d) infinity✔

113. A good voltage regulation of a transformer means
(a) output voltage fluctuation from no load to full load is least✔
(b) output voltage fluctuation with power factor is least
(c) difference between primary and secondary voltage is least
(d) difference between primary and secondary voltage is maximum

114. For a transformer, operating at constant load current, maximum efficiency will occur at
(a) 0.8 leading power factor
(b) 0.8 lagging power factor
(c) zero power factor
(d) unity power factor✔

115. Which of the following protection is normally not provided on small distribution transformers ?
(a) Overfluxing protection
(b) Buchholz relay✔
(c) Overcurrent protection
(d) All of the above

116. Which of the following acts as a protection against high voltage surges due to lightning and switching ?
(a) Horn gaps✔
(b) Thermal overload relays
(c) Breather
(d) Conservator

117. The efficiency of two identical transformers under load conditions can be determined by
(a) short-circuit test
(b) back-to-back test✔
(c) open circuit test
(d) any of the above

118. Which of the following insulating materials can withstand the highest temperature safely ?
(a) Cellulose
(b) Asbestos
(c) Mica✔
(d) Glass fibre

119. Which of the following parts of a transformer is visible from outside ?
(a) Bushings✔
(b) Core
(c) Primary winding
(d) Secondary wwinding

120. The noise produced by a transformer is termed as
(a) zoom
(b) hum✔
(c) ringing
(d) buzz

MCQs on transformer 81-100

81. The changes in volume of transformer cooling oil due to variation of atmospheric temperature during day and
night is taken care of by which part of transformer
(a) Conservator✔
(b) Breather
(c) Bushings
(d) Buchholz relay

82. An ideal transformer is one which has
(a) no losses and magnetic leakage✔
(b) interleaved primary and secondary windings
(c) a common core for its primary and secondary windings
(d) core of stainless steel and winding of pure copper metal

83. When a given transformer is run at its rated voltage but reduced frequency, its
(a) flux density remains unaffected
(b) iron losses are reduced
(c) core flux density is reduced
(d) core flux density is increased✔

84. In an actual transformer the iron loss remains practically constant from noload to fullload because
(a) value of transformation ratio remains constant
(b) permeability of transformer core remains constant
(c) core flux remains practically constant✔
(d) primary voltage remains constant

85. An ideal transformer will have maximum efficiency at a load such that
(a) copper loss = iron loss✔
(b) copper loss < iron loss
(c) copper loss > iron loss
(d) none of the above

86. If the supply frequency to the transformer is increased,”the iron loss will
(a) not change
(b) decrease
(c) increase✔
(d) any of the above

87. Negative voltage regulation is indicative that the load is
(a) capacitive only✔
(b) inductive only
(c) inductive or resistive
(d) none of the above

88. Iron loss of a transformer can be measured by
(a) low power factor wattmeter✔
(b) unity power factor wattmeter
(c) frequency meter
(d) any type of wattmeter

89. When secondary of a current transformer is open-circuited its iron core will be
(a) hot because of heavy iron losses taking place in it due to high flux density✔
(b) hot because primary will carry heavy current
(c) cool as there is no secondary current
(d) none of above will happen

90. The transformer laminations are insulated from each other by
(a) mica strip
(b) thin coat of varnish✔
(c) paper
(d) any of the above

91. Which type of winding is used in 3phase shell-type transformer ?
(a) Circular type
(b) Sandwich type✔
(c) Cylindrical type
(d) Rectangular type

92. During open circuit test of a transformer
(a) primary is supplied rated voltage✔
(b) primary is supplied full-load current
(c) primary is supplied current at reduced voltage
(d) primary is supplied rated kVA

93. Open circuit test on transformers is conducted to determine
(a) hysteresis losses
(b) copper losses
(c) core losses✔
(d) eddy current losses

94. Short circuit test on transformers is conducted to determine
(a) hysteresis losses
(b) copper losses✔
(c) core losses
(d) eddy current losses

95. For the parallel operation of single phase transformers it is necessary that they should have
(a) same efficiency
(b) same polarity✔
(c) same kVA rating
(d) same number of turns on the secondary side.

96. The transformer oil should have _____ volatility and _____ viscosity.
(a) low,low✔
(b) high,high
(c) low,high
(d) high,low

97. The function of breather in a transformer is
(a) to provide oxygen inside the tank
(b) to cool the coils during reduced load
(c) to cool the transformer oil
(d) to arrest flow of moisture when outside air enters the transformer✔

98. The secondary winding of which of the following transformers is always kept closed ?
(a) Step-up transformer
(b) Step-down transformer
(c) Potential transformer
(d) Current transformer✔

99. The size of a transformer core will depend on
(a) frequency
(b) area of the core
(c) flux density of the core material
(d) (a) and (b) both✔

100. N atural air coo ling is generally restricted for transformers up to
(a) 1.5 MVA✔
(b) 5 MVA
(c) 15 MVA
(d) 50 MVA

MCQs on transformer 61-80

61. The use of higher flux density in the transformer design
(a) reduces weight per kVA✔
(6) reduces iron losses
(c) reduces copper losses
(d) increases part load efficiency

62. The chemical used in breather for transformer should have the quality of
(a) ionizing air
(b) absorbing moisture✔
(c) cleansing the transformer oil
(d) cooling the transformer oil.

63. The chemical used in breather is
(a) asbestos fiber
(b) silica sand
(c) sodium chloride
(d) silica gel✔

64. An ideal transformer has infinite values of primary and secondary inductances. The statement is
(a) true
(b) false✔

65. The transformer ratings are usually expressed in terms of
(a) volts
(b) amperes
(c) kW
(d) kVA✔

66. The noise resulting from vibrations of laminations set by magnetic forces, is termed as
(a) magnetostrication
(b) boo
(c) hum✔
(d) zoom

67. Hysteresis loss in a transformer varies as CBmax = maximum flux density)
(a) Bmax
(b) Bmax1-6✔
(C) Bmax1-83
(d) B max

68. Material used for construction of transformer core is usually
(a) wood
(b) copper
(c) aluminium
(d) silicon steel✔

69. The thickness of laminations used in a transformer is usually
(a) 0.4 mm to 0.5 mm✔
(b) 4 mm to 5 mm
(c) 14 mm to 15 mm
(d) 25 mm to 40 mm

70. The function of conservator in a transformer is
(a) to project against’internal fault
(b) to reduce copper as well as core losses
(c) to cool the transformer oil
(d) to take care of the expansion and contraction of transformer oil due to variation of temperature of sur-roundings✔

71. The highest voltage for transmitting electrical power in India is
(a) 33 kV.
(6) 66 kV
(c) 132 kV
(d) 400 kV✔

72. In a transformer the resistance between its primary and secondary is
(a) zero
(b) 1 ohm
(c) 1000 ohms
(d) infinite✔

73. A transformer oil must be free from
(a) sludge
(b) odour
(c) gases
(d) moisture✔

74. A Buchholz relay can be installed on
(a) auto-transformers
(b) air-cooled transformers
(c) welding transformers
(d) oil cooled transformers✔

75. Gas is usually not liberated due to dissociation of transformer oil unless the oil temperature exceeds
(a) 150°C✔
(b) 80°C
(c) 100°C
(d) 50°C

76. The main reason for generation of harmonics in a transformer could be
(a) fluctuating load
(b) poor insulation
(c) saturation of core✔
(d) mechanical vibrations

77. Distribution transformers are generally designed for maximum efficiency around
(a) 90% load
(b) zero load
(c) 50% load✔
(d) 25% load

78. Which of the following property is not necessarily desirable in the material for transformer core ?
(a) Mechanical strength
(6) Low hysteresis loss
(c) High thermal conductivity✔
(d) High permeability

79. Star/star transformers work satisfactorily when
(a) load is unbalanced only
(b) load is balanced only✔
(c) on balanced as well as unbalanced loads
(d) none of the above

80. Delta/star transformer works satisfactorily when
(a) load is balanced only
(b) load is unbalanced only
(c) on balanced as well as unbalanced loads✔
(d) none of the above

MCQs on transformer 41-60

41. Buchholz’s relay gives warning and protection against
(a) electrical fault inside the transformer itself✔
(b) electrical fault outside the transformer in outgoing feeder
(c) for both outside and inside faults
(d) none of the above

42. The magnetising current of a transformer is usually small because it has
(a) small air gap✔
(b) large leakage flux
(c) laminated silicon steel core
(d) fewer rotating parts

43. Which of the following does not change in an ordinary transformer ?
(a) Frequency✔
(b) Voltage
(c) Current
(d) Any of the above

44. Which of the following properties is not necessarily desirable for the material for transformer core ?
(a) Low hysteresis loss
(b) High permeability
(c) High thermal conductivity✔
(d) Adequate mechanical strength

45. The leakage flux in a transformer depends upon
(a) load current✔
(b) load current and voltage
(c) load current, voltage and frequency
(d) load current, voltage, frequency and power factor

46. The path of the magnetic flux in transformer should have
(a) high reluctance
(b) low reactance✔
(c) high resistance
(d) low resistance

47. Noise level test in a transformer is a
(a) special test
(b) routine test
(c) type test✔
(d) none of the above

48. Which of the following is not a routine test on transformers ?
(a) Core insulation voltage test
(b) Impedance test
(c) Radio interference test✔
(d) Polarity test

49. A transformer can have zero voltage regulation at
(a) leading power factor✔
(b) lagging power factor
(c) unity power factor
(d) zero power factor

50. Helical coils can be used on
(a) low voltage side of high kVA transformers✔
(b) high frequency transformers
(c) high voltage side of small capacity transformers
(d) high voltage side of high kVA rating transformers

51. Harmonics in transformer result in
(a) increased core losses
(b) increased I2R losses
(c) magnetic interference with communication circuits
(d) all of the above✔

52. The core used in high frequency transformer is usually
(a) copper core
(b) cost iron core
(c) air core✔
(d) mild steel core

53. The full-load copper loss of a trans¬former is 1600 W. At half-load, the copper loss will be
(a) 6400 W
(b) 1600 W
(c) 800 W
(d) 400 W✔

54. The value of flux involved m the e.m.f. equation of a transformer is
(a) average value
(b) r.m.s. value
(c) maximum value✔
(d) instantaneous value

55. Silicon steel used in laminations mainly reduces
(a) hysteresis loss✔
(b) eddy current losses
(c) copper losses
(d) all of the above

56. Which winding of the transformer has less cross-sectional area ?
(a) Primary winding
(b) Secondary winding
(c) Low voltage winding
(d) High voltage winding✔

57. Power transformers are generally designed to have maximum efficiency around
(a) no-load
(b) half-load
(c) near full-load✔
(d) 10% overload

58. Which of the following is the main advantage of an auto-transformer over a two winding transformer ?
(a) Hysteresis losses are reduced
(b) Saving in winding material✔
(c) Copper losses are negligible
(d) Eddy losses are totally eliminated

59. During short circuit test iron losses are negligible because
(a) the current on secondary side is negligible
(b) the voltage on secondary side does not vary
(c) the voltage applied on primary side is low✔
(d) full-load current is not supplied to the transformer

60. Two transformers are connected in parallel. These transformers do not have equal percentage impedance. This is likely to result in
(a) short-circuiting of the secondaries
(b) power factor of one of the transformers is leading while that of the other lagging
(c) transformers having higher copper losses will have negligible core losses
(d) loading of the transformers not in proportion to their kVA ratings✔

MCQs on Transformer 21-40

21. Efficiency of a power transformer is of the order of
(a) 100 per cent
(b) 98 per cent✔
(c) 50 per cent
(d) 25 per cent

22. In a given transformer for given applied voltage, losses which remain constant irrespective of load changes are
(a) friction and windage losses
(b) copper losses
(c) hysteresis and eddy current losses✔
(d) none of the above

23. A common method of cooling a power transformer is
(a) natural air cooling
(b) air blast cooling
(c) oil cooling✔
(d) any of the above

24. The no load current in a transformer lags behind the applied voltage by an angle of about
(a) 180°
(b) 120″
(c) 90°
(d) 75°✔

25. In a transformer routine efficiency depends upon
(a) supply frequency
(b) load current
(c) power factor of load
(d) both (b) and (c)✔

26. In the transformer the function of a conservator is to
(a) provide fresh air for cooling the transformer
(b) supply cooling oil to transformer in time of need
(c) protect the transformer from damage when oil expends due to heating✔
(d) none of the above

27. Natural oil cooling is used for transformers up to a rating of
(a) 3000 kVA✔
(b) 1000 kVA
(c) 500 kVA
(d) 250 kVA

28. Power transformers are designed to have maximum efficiency at
(a) nearly full load✔
(b) 70% full load
(c) 50% full load
(d) no load

29. The maximum efficiency of a distribution transformer is
(a) at no load
(b) at 50% full load✔
(c) at 80% full load
(d) at full load

30. Transformer breaths in when
(a) load on it increases
(b) load on it decreases✔
(c) load remains constant
(d) none of the above

31. No-load current of a transformer has
(a) has high magnitude and low power factor
(b) has high magnitude and high power factor
(c) has small magnitude and high power factor
(d) has small magnitude and low power factor✔

32. Spacers are provided between adjacent coils
(a) to provide free passage to the cooling oil✔
(b) to insulate the coils from each other
(c) both (a) and (b)
(d) none of the above

33. Greater the secondary leakage flux
(a) less will be the secondary induced e.m.f.✔
(b) less will be the primary induced e.m.f.
(c) less will be the primary terminal voltage
(d) none of the above

34. The purpose of providing iron core in a step-up transformer is
(a) to provide coupling between primary and secondary
(b) to increase the magnitude of mutual flux
(c) to decrease the magnitude of mag-netizing current✔
(d) to provide all above features

35. The power transformer is a constant
(a) voltage device
(b) current device
(c) power device
(d) main flux device✔

36. Two transformers operating in parallel will share the load depending upon their
(a) leakage reactance
(b) per unit impedance✔
(c) efficiencies
(d) ratings

37. If R2 is the resistance of secondary winding of the transformer and K is the transformation ratio then the equivalent secondary resistance referred to primary will be
(a) R2/VK
(b) R2IK2✔
(c) R22!K2
(d) R22/K

38. What will happen if the transformers working in parallel are not connected with regard to polarity ?
(a) The power factor of the two trans-formers will be different from the power factor of common load
(b) Incorrect polarity will result in dead short circuit✔
(c) The transformers will not share load in proportion to their kVA ratings
(d) none of the above

39. If the percentage impedances of the two transformers working in parallel are different, then
(a) transformers will be overheated
(b) power factors of both the transformers will be same
(c) parallel operation will be not possible
(d) parallel operation will still be possible, but the power factors at which the two transformers operate will be different from the power factor of the common load✔

40. In a transformer the tappings are generally provided on
(a) primary side
(b) secondary side
(c) low voltage side✔
(d) high voltage side

MCQs on Transformer 1-20

1. Which of the following does not change in a transformer ?
(a) Current
(b) Voltage
(c) Frequency✔
(d) All of the above

2. In a transformer the energy is conveyed from primary to secondary
(a) through cooling coil
(b) through air
(c) by the flux✔
(d) none of the above

3. A transformer core is laminated to
(a) reduce hysteresis loss
(b) reduce eddy current losses✔
(c) reduce copper losses
(d) reduce all above losses

4. The degree of mechanical vibrations produced by the laminations of a transformer depends on
(a) tightness of clamping
(b) gauge of laminations
(c) size of laminations
(d) all of the above✔

5. The no-load current drawn by transformer is usually what per cent of the full-load current ?
(a) 0.2 to 0.5 percent
(b) 2 to 5 percent✔
(c) 12 to 15 percent
(d) 20 to 30 percent

6. The path of a magnetic flux in a transformer should have
(a) high resistance
(b) high reluctance
(c) low resistance
(d) low reluctance✔

7. No-load on a transformer is carried out to determine
(a) copper loss
(b) magnetising current
(c) magnetising current and loss✔
(d) efficiency of the transformer

8. The dielectric strength of transformer oil is expected to be
(a) lkV
(b) 33 kV✔
(c) 100 kV
(d) 330 kV

9. Sumpner’s test is conducted on trans-formers to determine
(a) temperature✔
(b) stray losses
(c) all-day efficiency
(d) none of the above

10. The permissible flux density in case of cold rolled grain oriented steel is around
(a) 1.7 Wb/m2✔
(b) 2.7 Wb/m2
(c) 3.7 Wb/m2
(d) 4.7 Wb/m2

11. The efficiency of a transformer will be maximum when
(a) copper losses = hysteresis losses
(b) hysteresis losses = eddy current losses
(c) eddy current losses = copper losses
(d) copper losses = iron losses✔

12. No-load current in a transformer
(a) lags behind the voltage by about 75°✔
(b) leads the voltage by about 75°
(c) lags behind the voltage by about 15°
(d) leads the voltage by about 15°

13. The purpose of providing an iron core in a transformer is to
(a) provide support to windings
(b) reduce hysteresis loss
(c) decrease the reluctance of the magnetic path✔
(d) reduce eddy current losses

14. Which of the following is not a part of transformer installation ?
(a) Conservator
(b) Breather
(c) Buchholz relay
(d) Exciter✔

15. While conducting short-circuit test on a transformer the following side is short circuited
(a) High voltage side
(b) Low voltage side✔
(c) Primary side
(d) Secondary side

16. In the transformer following winding has got more cross-sectional area
(a) Low voltage winding✔
(b) High voltage winding
(c) Primary winding
(d) Secondary winding

17. A transformer transforms
(a) voltage
(b) current
(c) power✔
(d) frequency

18. A transformer cannot raise or lower the voltage of a D.C. supply because
(a) there is no need to change the D.C. voltage
(b) a D.C. circuit has more losses
(c) Faraday’s laws of electromagnetic induction are not valid since the rate of change of flux is zero✔
(d) none of the above

19. Primary winding of a transformer
(a) is always a low voltage winding
(b) is always a high voltage winding
(c) could either be a low voltage or high voltage winding✔
(d) none of the above

20. Which winding in a transformer has more number of turns ?
(a) Low voltage winding
(b) High voltage winding✔
(c) Primary winding
(d) Secondary winding

MCQ on synchronous motor 102-120

102. Synchronous motors are generally not self-starting because
(a) the direction of rotation is not fixed
(b) the direction of instantaneous torque reverses after half cycle✔
(c) startes cannot be used on these machines
(d) starting winding is not provided on the machines

103. In case one phase of a three-phase synchronous motor is short-circuited the motor will
(a) not start✔
(b) run at 2/3 of synchronous speed
(c) run with excessive vibrations
(d) take less than the rated load

103. A pony motor is basically a
(a) small induction motor✔
(b) D.C. series motor
(c) D.C. shunt motor
(d) double winding A.C./D.C. motor

104. A synchronous motor can develop synchronous torque
(a) when under loaded
(b) while over-excited
(c) only at synchronous speed✔
(d) below or above synchronous speed

105. A synchronous motor can be started by
(a) pony motor
(b) D.C. compound motor
(c) providing damper winding
(d) any of the above✔

106. A three-phase synchronous motor will have
(a) no slip-rings
(b) one slip-ring
(c) two slip-rings✔
(d) three slip-rings

107. Under which of the following conditions hunting of synchronous motor is likely to occur ?
(a) Periodic variation of load✔
(b) Over-excitation
(c) Over-loading for long periods
(d) Small and constant load

108. When the excitation of an unloaded salient pole synchronous motor suddenly gets disconnected
(a) the motor stops✔
(b) it runs as a reluctance motor at the same speed
(c) it runs as a reluctance motor at a lower speed
(d) none of the above

109. When V is the applied voltage, then the breakdown torque of a synchronous motor varies as
(a) V✔
(b) V312
(c) V2
(d) 1/V

110. The power developed by a synchronous motor will be maximum when the load angle is
(a) zero
(b) 45°
(c) 90°✔
(d) 120°

111. A synchronous motor can be used as a synchronous capacitor when it is
(a) under-loaded
(b) over-loaded
(c) under-excited
(d) over-excited✔

112. A synchronous motor is running on a load with normal excitation. Now if the load on the motor is increased
(a) power factor as well as armature current will decrease
(b) power factor as well as armature current will increase
(c) power factor will increase but armature current will decrease
(d) power factor will decrease and armature current will increase✔

113. Mostly, synchronous motors are of
(a) alternator type machines
(6) induction type machines
(c) salient pole type machines✔
(d) smooth cylindrical type machines

114. The synchronous motor is not inherently self-starting because
(a) the force required to accelerate the rotor to the synchronous speed in an instant is absent✔
(b) the starting device to accelerate the rotor to near synchronous speed is absent
(c) a rotating magnetic field does not have enough poles
(d) the rotating magnetic field is produced by only 50 Hz frequency currents

115. As the load is applied to a synchronous motor, the motor takes more armature current because
(a) the increased load has to take more current
(b) the rotor by shifting its phase backward causes motor to take more current✔
(c) the back e.m.f. decreases causing an increase in motor current
(d) the rotor strengthens the rotating field casuing more motor current

116. Synchronous motor always runs at
(a) the synchronous speed✔
(b) less than synchronous speed
(c) more than synchronous speed
(d) none of the above

117. An over-excited synchronous motor takes
(a) leading current✔
(b) lagging current
(c) both (a) and (b)
(d) none of the above

118. The working of a synchronous motor is similar to
(a) gear train arrangement
(b) transmission of mechancial power by shaft✔
(c) distribution transformer
(d) turbine
(e) none of the above

119. The minimum armature current of the synchronous motor corresponds to operation at
(a) zero power factor leading
(b) unity power factor✔
(c) 0.707 power factor lagging
(d) 0.707 power factor leading

120. In a synchronous motor, the magnitude of stator back e.m.f. £& depends on
(a) d.c. excitation only✔
(b) speed of the motor
(c) load on the motor
(d) both the speed and rotor flux

21. If load (or torque) angle of a 4-pole synchronous motor is 6° electrical, its value in mechanical degrees is
(a) 2
(b) 3✔
(c) 4
(d) 6

MCQ on synchronous motor 81-101

81. For V-curves for a synchronous motor the graph is drawn between
(a) field current and armature current✔
(b) terminal voltage and load factor
(c) power factor and field current
(d) armature current and power factor

82. The back e.m.f. of a synchronous motor depends on
(a) speed
(b) load
(c) load angle✔
(d) all of the above

83. A synchronous motor can operate at
(a) lagging power factor only
(6) leading power factor only
(c) unity power factor only
(d) lagging, leading and unity power factors✔

84. In a synchronous motor which loss varies with load ?
(a) Windage loss
(b) Bearing friction loss
(c) Copper loss✔
(d) Core loss

85. A synchronous motor can be made self starting by providing
(a) damper winding on rotor poles
(b) damper winding on stator
(c) damper winding on stator as well as rotor poles
(d) none of the above✔

86. The oscillations in a synchronous motor can be damped out by
(a) maintaining constant excitation
(b) running the motor on leading power factors
(c) providing damper bars in the rotor pole faces✔
(d) oscillations cannot be damped

87. The shaft of synchronous motor is made of
(a) mild steel✔
(b) chrome steel
(c) alnico
(d) stainless steel

88. When the field of a synchronous motor is under-excited, the power factor will be
(a) leading
(b) lagging✔
(c) unity
(d) zero

89. The speed regulation of a synchronous motor is always
(a) 1%
(b) 0.5%
(c) positive
(d) zero✔

90. The percentage slip in case of a synchronous motor is
(a) 1%
(b) 100%
(c) 0.5%
(d) zero✔

91. The operating speed of a synchronous motor can be changed to new fixed value by
(a) changing the load
(b) changing the supply voltage
(c) changing frequency✔
(d) using brakes

92. A synchronous motor will always stop when
(a) supply voltage fluctuates
(b) load in motor varies
(c) excitation winding gets disconnected✔
(d) supply voltage frequency changes

93. riunting in a synchronous motor takes place
(a) when supply voltage fluctuates
(b) when load varies✔
(c) when power factor is unity
(d) motor is under loaded

94. When load on an over-excited or under excited synchronous*motor is increased, rate of change of its armature current as compared with that of power factor is
(a) more
(b) less✔
(c) equal
(d) twice

95. The rotor copper losses, in a synchronous motor, are met by
(a) d.c. source✔
(b) armature input
(c) motor input
(d) supply lines

96. The maximum power developed in a synchronous motor occurs at a coupling angle of
(a) 30°
(b) 60°
(c) 90°✔
(d) 180°

97. When the stator windings are connected in such a fashion that the number of poles are made half, the speed of the rotor of a synchronous motor
(a) remains same as the original value
(b) decreases to half the original value
(c) tends to becomes zero
(d) increases to two times the original value✔

98. In which of the following motors the stator and rotor magnetic field rotate at the same speed ?
(a) Universal motor
(b) Synchronous motor✔
(c) Induction motor
(d) Reluctance motor

99. Synchronsizingpower of a synchronous machine is
(a) direcly proportional to the synchronous reactance
(b) inversely proportional to the✔ synchronous reactance
(c) equal to the synchronous reactance
(d) none of the above

100. Synchronous motors are
(a) not-self starting✔
(b) self-starting
(c) essentially self-starting
(d) none of the above

101. The standard full-load power factor ratings for synchronous motors are
(a) zero or 0.8 leading
(b) unity or 0.8 lagging
(c) unity or 0.8 leading✔
(d) unity or zero

MCQ on synchronous motor 61-80

61. Slip rings are usually made of
(a) carbon or graphite
(b) brass or steel✔
(c) silver or gold
(d) copper or aluminium

62. An over excited synchronous motor is used for
(a) fluctuating loads
(b) variable speed loads
(c) low torque loads
(d) power factor corrections✔

63. When the voltage applied to a synchronous motor is increased, which of the following will reduce ?
(a) Stator flux
(b) Pull in torque
(c) Both (a) and (b)
(d) None of the above✔

64. The efficiency of a properly designed synchronous motor will usually fall in range
(a) 60 to 70%
(6) 75 to 80%
(c) 85 to 95%✔
(d) 99 to 99.5%

65. To limit the operating temperature an electrical machine should have proper
(a) voltage rating
(b) current rating✔
(c) power factor
(d) speed

66. Slip-rings in a synchronous motor carry
(a) direct current✔
(b) alternating current
(c) no current
(d) all of the above

67. A synchronous machine with large air gap has
(a) a higher value of stability limit
(6) a small value of inherent regulation
(c) a higher synchronizing power which makes the machine less sensitive to load variations
(d) all of the above✔

68. The armature current of the synchronous motor has higher values for
(a) high excitation only
(b) low excitation only
(c) both (a) and (b)✔
(d) none of the above

69. In a synchronous motor running with fixed excitation, when the load is increased three times, its torque angle becomes approximately
(a) one-third
(b) twice
(c) thrice✔
(d) six times

70. The angle between the rotating stator flux and rotor poles is called _____ angle.
(a) torque✔
(b) obtuse
(c) synchronizing
(d) power factor

71. Which of the following methods is used to start a synchronous motor ?
(a) Damper winding
(b) Star-delta starter
(c) Damper winding in conjunction with star-delta starter✔
(d) Resistance starter in the armature circuit

72. When the rotor speed, in a synchronous machine, becomes more than the synchronous speed during hunting, the damper bars develop
(a) inductor motor torque
(b) induction generator torque✔
(c) synchronous motor torque
(d) d.c. motor toque

73. An important advantage of a synchronous motor over wound round induction motor is that
(a) its power factor may be varied at will✔
(b) its speed is independent of supply frequency
(c) its speed may be controlled more easily
(d) none of the above

74. The mechanical displacement of the rotor with respect to the stator, in polyphase multipolar synchronous motors running at full load, is of the order of
(a) zero degree
(b) two degrees
(c) five degrees✔
(d) ten degrees

75. Power factor of a synchronous motor is unity when
(a) the armature current is maximum
(b) the armature current is minimum✔
(c) the armature current is zero
(d) none of the above

76. Change of D.C. excitation of a synchronous motor changes
(a) applied voltage of the motor
(b) motor speed
(c) power factor of power drawn by the motor✔
(d) any of the above

77. While starting a synchronous motor by induction motor action, field winding is usually
(a) connected to D.C. supply
(b) short-circuited by low resistance✔
(c) kept open-circuited
(d) none of the above

78. A synchronous motor running with normal excitation adjusts to load increases essentially by increase in
(a) back e.m.f.
(b) armature current✔
(c) power factor
(d) torque angle

79. A synchronous motor has better power factor as compared to that of an equivalent induction motor. This is mainly because
(a) synchronous motor has no slip
(b) stator supply is not required to produce magnetic field✔
(c) mechanical load on the rotor remains constant
(d) synchronous motor has large airgap

80. A synchronous motor working at leading power factor can be used as
(a) voltage booster
(b) phase advancer✔
(c) noise generator
(d) mechanical synchronizer

MCQ on synchronous motor 41-60

41. If in a synchronous motor, driving mechanical load and drawing current at lagging power factor from constant voltage supply, its field excitation is increased, then its power factor
(a) become more
(b) become less✔
(c) remain constant
(d) none of the above

42. A synchronous motor installed at the receiving end substation operates with such an excitation that it takes power at lagging power factor. Now if the applied voltage of the synchronous motor goes down, the power factor of the synchronous motor will
(a) remain same
(b) go down
(c) improve✔
(d) none of the above

43. While starting a salient pole synchronous motor by induction motor action and connecting field discharge resistance across field, starting and accelerting torque is produced by
(a) induction motor torque in field winding
(b) induction motor torque in damper winding
(c) eddy current and hysteresis torque in pole
(d) all of the above methods✔

45. Armature of a synchronous machine is
(a) of reducing number of slip rings on the rotor
(b) armature is associated with large power as compared to the field circuits
(c) of difficulty of providing high voltage insulation on rotor
(d) all of the above reasons✔

46. If excitation of a synchronous motor running with a constant load is decreased from its normal value, ignoring effects of armature reaction, it leads to
(a) increase in both armature current and power factor angle✔
(b) increase in back e.m.f. but decrease in armature current
(c) increase in both armature current and power factor which is lagging
(d) increase in torque angle but decrease in back e.m.f.

47. When a 3-phase synchronous generator is supplying a zero power factor lagging load, the armature field affects the main field in the following way
(a) augments it directly
(b) directly opposes it✔
(c) cross-magnetises it
(d) none of the above

48. Stability of a synchronous machine
(a) decreases with increase in its excitation
(b) increases with increase in its excitation✔
(c) remains unaffected with increase in excitation
(d) any of the above

49. The power factor of a synchronous motor is better than that of induction motor because
(a) stator supply is relieved of responsibility of producing magnetic field✔
(b) mechanical load on the motor can be adjusted
(c) synchronous motor runs at synchronous speed
(d) synchronous motor has large air gap

50. If in a synchronous motor, driving a given mechanical load and drawing current at a leading power factor from constant voltage supply its field excitation is increased, its power factor
(a) will become more
(b) will become less✔
(c) will remain unchanged
(d) none of the above.

51. A synchronous motor is running with normal excitation. When the load is increased, the armature current drawn by it increases because
(a) speed of the motor is reduced
(b) power factor is decreased
(c) Eb (back e.m.f.) becomes less than V (applied voltage)
(d) Er (net resultant voltage) in armature is increased✔

52. If one-phase of a 3-phase synchronous motor is short-circuited, motor
(a) will refuse to start✔
(b) will overheat in spots
(c) will not come upto speed
(d) will fail to pull into step

53. If the field circuit of an unloaded salientpole synchronous motor gets suddenly open-circuited, then
(a) it runs at a slower speed
(b) the motor stops✔
(c) it continues to run at the same speed
(d) it runs at a very high speed

54. In which of the following motors the stator and rotor fields rotate simultaneously ?
(a) D.C. motor
(b) Reluctance motor
(c) Universal motor
(d) Synchronous motor✔
(e) Induction motor

55. The speed of a synchronous motor
(a) increases as the load increases
(b) decreases as the load decreases
(c) always remains constant✔
(d) none of the above

56. A rotory converter can also be run as a
(a) d.c. shunt motor
(b) d.c. series motor
(c) d.c. compound motor
(d) induction motor
(e) synchronous motor
Ans: e

57. The maximum speed variation in a 3-phase synchronous motor is
(a) 10 per cent
(b) 6 per cent
(c) 4 per cent
(d) zero✔

58. Which of the following resistances can be measured by conducting insulation resistance test on a synchronous motor ?
(a) Phase to phase winding resistance
(b) Stator winding to earthed frame
(c) Rotor winding to earthed shaft
(d) All of the above✔

59. Due to which of the following reasons a synchronous motor fails to pull into synchronism after applying D.C. field current ?
(a) High field current
(b) Low short circuit ratio
(c) High core losses
(d) Low field current✔

60. Which of the following motors will be used in electric clocks ?
(a) D.C. shunt motor
(b) D.C. series motor
(c) A.C. induction motor
(d) A.C. synchronous motor✔

MCQ on synchronous motor 21-40

21. In a synchronous motor, the maximum power developed depends on all of the following except
(a) rotor excitation
(b) maximum value of coupling angle
(c) direction of rotation✔
(d) supply voltage

22. In a 3-phase synchronous motor, the negative phase sequence exists when the motor is
(a) supplied with unbalanced voltage✔
(b) under-loaded
(c) over-loaded
(d) none of the above

23. In a synchronous motor, damper windings are provided on
(a) stator frame
(b) rotor shaft
(c) pole faces✔
(d) none of the above

24. The induced e.m.f. in a synchronous motor working on leading power factor will be
(a) more than the supply voltage✔
(b) less than the supply voltage
(c) equal to the supply voltage

25. The effect of increasing the load on a synchronous motor running with normal excitation is to
(a) decrease both armature current and power factor
(b) decrease armature current but increase power factor
(c) increase armature current but decrease power factor✔
(d) increase both its armature current and power factor

26. The net armature voltage of a synchronous motor is equal to the
(a) vector sum of Eb and V
(b) arithmetic sum of Eb and V
(c) arithmetic difference of Eb and V✔
(d) vector difference of Eh and V

27. The ratio of starting torque to running torque in a synchronous motor is
(a) zero✔
(b) one
(c) two
(d) infinity

28. In a synchronous motor, the magnitude of stator back e.m.f. Eb depends on
(a) load on the motor
(b) d.c. excitation only✔
(c) both the speed and rotor flux
(d) none of the above

29. A 3-phase synchronous motor is running clockwise. If the direction of its field current is reversed
(a) the motor will stop
(b) the motor continue to run in the same direction✔
(c) the winding of the motor will burn
(d) the motor will run in the reverse direction

30. The magnitude of field flux in a 3-phase synchronous motor
(a) remains constant at all loads✔
(b) varies with speed
(c) varies with the load
(d) varies with power factor

31. The torque angle, in a synchronous motor, is the angle between
(a) the supply voltage and the back e.m.f.
(b) magnetising current and back e.m.f.
(c) the rotating stator flux and rotor poles✔
(d) none of the above

32. Hunting in a synchronous motor cannot be due to
(a) windage friction✔
(b) variable load
(c) variable frequency
(d) variable supply voltage

33. By which of the following methods the constant speed of a synchronous motor can be changed to new fixed value ?
(a) By changing the supply frequency✔
(b) By interchanging any two phases
(c) By changing the applied voltage
(d) By changing the load.

34. In a synchronous motor, V-curves represent relation between
(a) armature current and field current✔
(b) power factor and speed
(c) field current and speed
(d) field current and power factor

35. In a 3-phase, 4-pole, 50 Hz synchronous motor, the frequency, pole number and load torque all are halved. The motor speed will be
(a) 3000 r.p.m.
(b) 1500 r.p.m.✔
(c) 750 r.p.m.
(d) none of the above

36. A synchronous motor connected to infinite bus-bars has at constant full load, 100% excitation and unity power factor. On changing the excitation only, the armature current will have
(a) no change of power factor
(b) lagging power factor with over-excitation
(c) leading power factor with under-excitation
(d) leading power factor with over-excitation✔

37. Which of the following motors is non-self starting ?
(a) D.C. series motor
(b) synchronous motor✔
(c) Squirrel cage induction motor
(d) Wound round induction motor

38. In a synchronous motor it the back e.m.f. generated in the armature at noload is approximately equal to the applied voltage, then
(a) the motor is said to be fully loaded
(b) the torque generated is maximum
(c) the excitation is said to be zero per cent
(d) the excitation is said to be hundred per cent✔

39.In a synchronous motor, the damping winding is generally used to
(a) prevent hunting and provide the starting torque✔
(b) reduce the eddy currents
(c) provide starting torque only
(d) reduce noise level
(e) none of the above

40. If the field of a synchronous motor is underexcited, the power factor will be
(a) zero
(b) unity
(c) lagging✔
(d) leading

MCQ synchronous motor 1-20

1. The maximum constant load torque under which a synchronous motor will pull into synchronism at rated rotor supply voltage and frequency is known as
(a) pull-up torque
(b) pull-in torque✔
(c) pull-out torque
(d) none of the above

2. A synchronous machine with low value of short-circuit ratio has
(a) lower stability limit✔
(6) high stability limit
(c) good speed regulation
(d) good voltage regulation
(e) none of the above

3. The construction of a synchronous motor resembles
(a) a series motor
(b) an induction motor
(c) an alternator✔
(d) a rotary converter

4. If the field winding of an unloaded salient pole synchronous motor is open circuited, the motor will
(a) stop✔
(b) run as induction motor
(c) function as static condenser
(d) burn with dense smoke

5. For power factor correction, synchronous motors operate at
(a) no-load and greatly over-excited fields✔
(b) no-load and under-excited fields
(c) normal load with minimum excitation
(d) normal load with zero excitation

6. The maximum torque which a synchronous motor will develop at rest for any angular position of the rotor, at rated stator supply voltage and frequency, is known as
(a) locked-rotor torque✔
(b) synchronous torque
(c) pull up torque
(d) reluctance torque

7. Exciters of synchronous machines are
(a) d.c. shunt machines✔
(b) d.c. series machines
(c) d.c. compound machines
(d) any of the above

8. The coupling angle or load angle of synchronous motor is defined as the angle between the
(a) rotor and stator teeth
(b) rotor and the stator poles of opposite polarity✔
(c) rotor and the stator poles of the same polarity
(d) none of the above

9. If the synchronous motor, properly synchronised to the supply is running on no load and is having negligible loss
then
(a) the stator current will be zero✔
(b) the stator current will be very small
(c) the stator current will be very high
(d) the back e.m.f. will be more than the supply voltage
(e) none of the above

10 The armature current of the synchronous motor
(a) has large values for low excitation i niy
(b) has large values for high excitation only
(c) has large values for low and high excitation✔
(d) any of the above

11. The maximum power developed in a synchronous motor will depend on
(a) the rotor excitation only
(b) the supply voltage only
(c) the rotor excitation and supply volt-age both
(d) the rotor excitation, supply voltage and maximum value of coupling angle (90°)✔

12. A synchronous motor which works on a leading power factor and does not drive a mechanical load is called as
(a) static condenser
(b) condenser
(c) synchronous condenser✔
(d) none of the above

13. A synchronous motor develops maximum power when load angle is
(a) 45°
(b) 60°
(c) 90°✔
(d) 120°

14. In a synchronous motor, the breakdown torque is
(a) directly proportional to applied voltage✔
(b) directly proportional to the square of the applied voltage
(c) inversely proportional to applied voltage
(d) none of the above

15. The maximum value of torque that a synchronous motor can develop without losing its synchronism, is known as
(a) slip torque
(b) pull-out torque
(c) breaking torque
(d) synchronising torque✔

16. In a synchronous motor, the armature current has large values for
(a) high excitation only
(b) low excitation only
(c) both high and low excitation✔
(d) none of the above

17. Which of the following losses, in a synchronous motor, does not vary with load?
(a) Windage loss✔
(b) Copper losses
(c) Any of the above
(d) None of the above

18. The size of a synchronous motor decreases with the increase in
(a) flux density✔
(b) horse power rating
(c) speed
(d) all of the above

19. Which of the following losses is not dissipated by the stator core surface in a synchronous motor ?
(a) Eddy current losses in the conductors
(b) Iron losses in the stator
(c) Copper losses in the slot portion of the conductors
(d) Windage losses✔

20. The duration of sudden snort-circuit test on a synchronous motor is usually about
(a) one hour
(b) one minute
(c) one second✔
(d) none of the above

MCQ on DC grnerator 81-100

81. A 220 V D.C. generator is run at full speed without any excitation. The open circuit voltage will be
(a) zero
(b) about 2 V✔
(c) about 50 V
(d) 220 V

82. In a separately excited generator supplying rated load the armature reaction ,
(a) is always present✔
(b) is always absent
(c) may be sometimes present
(d) none of the above

83. If residual magnetism is present in a D.C. generator, the induced e.m.f. at zero speed will be
(a) zero✔
(b) small
(c) the same as rated voltage
(d) high

84. Armature reaction in a generator results in
(a) demagnetisation of leading pole tip and magnetisation of trailing pole tip✔
(b) demagnetisation of trailing pole tip and magnetisation of leading pole tip
(c) damagnetising the center of all poles
(d) magnetising the center of all poles

85. Following energized winding of a D.C. machine should not be opened as it would produce high inductive voltage which may be dangerous to personnel and may cause its own insulation failure.
(a) Series field
(b) Compensating field
(c) Inter pole field✔
(d) Shunt field

86. Wave winding is composed of
(a) any even number of conductors
(b) any odd number of conductors
(c) that even number which is exact multiple of poles + 2✔
(d) that even number which is exact multiple of poles

87. The critical resistance of the D.C. generator is the resistance of
(a) field✔
(b) brushes
(c) armature
(d) load

88. When two D.C. series generators are running in parallel, an equilizer bar is used
(a) to increase the speed and hence generated e.m.f.
(b) to increase the series flux
(c) so that two similar machines will pass approximately equal currents to the load✔
(d) to reduce the combined effect of ar-mature reaction of both machines

89. Which of the following generating machine will offer constant voltage on all loads ?
(a) Self-excited generator
(b) Separately excited generator
(c) Level compounded generator .✔
(d) All of the above

90. Which of the following generators will be preferred if they are required to be run in parallel ?
(a) Shunt generators✔
(b) Series generators
(c) Compound generators
(d) None of the above

91. Two generators are running in parallel. One of the generators may run as motor for which of the following reasons ?
(a) The direction of that generator is reversed
(b) The speed of that generator is increased
(c) The field of that generator is weakened
(d) That generator takes large share of loads✔

92. A D.C. generator works on the principle of
(a) Lenz’s law
(b) Ohm’s law
(c) Faraday’s law of electromagnetic induction✔
(d) none of the above

93. A series generator can self-excite
(a) only if the load current is zero
(b) only if the load current is not zero✔
(c) irrespective of the value of load current
(d) none of the above

94. A shunt generator can self-excite
(a) only if the resistance of the field circuit is less than critical value✔
(b) only if the resistance of the field circuit is greater than critical value
(c) irrespective of the value of the resistance in the field circuit

95. The terminal voltage of a series generator is 150 V when the load current is 5 A. If the load current is increased to 10 A, the terminal voltage will be
(a) 150 V
(b) less than 150 V
(c) greater than 150 V✔
(d) none of the above

96. The open circuit voltage of a compound generator is 250 V. At full load the terminal voltage
(a) will be less than 250 V
(b) will always be 250 V
(c) may be greater or less than 250 V✔
(d) none of the above

97. Two D.C. shunt generators, each with armature resistance of 0.02 ohm and field resistance of 50 ohm run in parallel and supply a total current of 1000 amperes to the load circuit. If their e.m.fs. are 270 V and 265 V, their bus bar voltage will be
(a) 270 V
(b) 267.5 V✔
(c) 265 V
(d) 257.4 V

98. The essential condition for parallel operation of two D.C. generators is that they have ‘
(a) same kW rating
(b) the same operation r.p.m.
(c) the same drooping voltage characteristics✔
(d) same percentage regulation
ohmic drop – armature reaction
(d) magnetisation characteristic = external characteristic
99. With a D.C. generator which of the following regulation is preferred ?
(a) 100% regulation
(b) infinite regulation
(c) 50% regulation
(d) 1% regulation✔
100. Which generator would you prefer for feeding long D.C. transmission lines ?
(a) Series generator
(b) Shunt generator
(c) Over compound generator✔
(d) Flat compound generator

MCQ on DC generator 61-80

61. Armature coil is short circuited by brushes when it lies
(a) along neutral axis✔
(b) along field axis
(c) in any of the above positions
(d) in none of the above positions

62. A cumulatively compounded long shunt generator when operating as a motor would be
(a) cumulatively compounded long shunt
(b) differentially compounded long shunt✔
(c) cumulatively compounded short shunt
(d) differentially compounded short shunt

63. To avoid formation of grooves in the commutator of a D.C. machine
(a) the brushes of opposite polarity should track each other✔
(b) the brushes of same polarity should track each other
(c) brush position has no effect on the commutator grooving

64. The following constitute short-circuit in the armature winding.
(a) Insulation failure between two commutator bars
(b) Insulation failure between two turns of a coil
(c) Two of more turns of the same coil getting grounded
(d) All of the above✔

65. The rapid wear of brushes takes place due to
(a) abrasion from dust
(b) excessive spring pressure
(c) rough commutator bars
(d) all of the above factors✔

66. Number of tappings for each equilizer ring is equal to
(a) number of pole pairs✔
(b) number of poles
(c) number of parallel paths
(d) number of commutator segments

67. A D.C. generator can be considered as
(a) rectifier
(b) primemover
(c) rotating amplifier✔
(d) power pump

68. In any rotating machine that part which houses the conductors and in which e.m.f. induced is to be utilised is called
(a) rotor
(b) stator
(c) field
(d) armature✔

69. In a D.C. machine stray loss is the sum of
(a) total copper loss and mechanical loss
(b) armature copper loss and iron loss
(c) shunt field copper loss and mechanical loss
(d) iron loss and mechanical loss✔

70. Lap winding is composed of
(a) any even number of conductors✔
(b) any odd number of conductors
(c) that even number which is exact multiple of poles + 2
(d) that even number which is exact multiple of poles

71. In a D.C. generator in case the resistance of the field winding is increased, then output voltage will
(a) increase
(b) decrease✔
(c) remain unaffected
(d) fluctuate heavily

72. An exciter for a turbo generator is a
(a) separately excited generator
(b) shunt generator✔
(c) series generator
(d) compound generator

73. In case of a flat compounded generator
(a) voltage generated is less than the rated voltage
(b) generated voltage is proportional to the load on the generator
(c) voltage remains constant irrespective of the load✔
(d) speed varies in proportion to the load on the generator

74. Which of the following generator will have negligible terminal voltage while running on no-load ?
(a) Series generator✔
(b) Shunt generator
(c) Compound generator
(d) Separately excited generator

75. Which of the following D.C. generators will be in a position to build up without any residual magnetism in the poles ?
(a) Series generator
(b) Shunt generator
(c) Compound generator
(d) None of the above✔

76. In over compounded generator, full load terminal voltage is
(a) almost zero
(b) less than no load terminal voltage
(c) more than no load terminal voltage✔
(d) equal to no-load terminal voltage

77. In a level compounded D.C. generator, full load terminal voltage is
(a) negligibly low
(b) equal to no-load terminal voltage✔
(c) more than no-load terminal voltage
(d) less than no-load terminal voltage

78. The terminal voltage of a D.C. shunt generator drops on load because of all of the following reasons except
(a) armature reaction
(b) armature resistance drop
(c) field weakening due to armature reaction and armature
(d) commutation✔

79. In a D.C. generator
(a) external resistance = internal char-acteristic – armature reaction
(b) internal characteristic = magnetisation characteristic – ohmic drop
(c) external characteristic = magnetisation characteristic – ohmic drop – armature reaction✔
(d) magnetisation characteristic = external characteristic

80. A sinusoidal voltage of 5 Hz is applied to the field of a shunt generator. The armature voltage wave
(a) will be zero
(b) will be of 5 Hz✔
(c) will be of 5 xiVHz
(d) will be of v Hz 5

MCQ on DC generator 41-60

41. In D.C. generators, current to the external circuit from armature is given through
(a) commutator✔
(b) solid connection
(c) slip rings
(d) none of above

42. Brushes of D.C. machines are made of
(a) carbon✔
(b) soft copper
(c) hard copper
(d) all of above

43. If B is the flux density, I the length of conductor and v the velocity of conductor, then induced e.m.f. is given by
(a)Blv✔
(b)Blv2
(c)Bl2v
(d)Bl2v2

44. In case of a 4-pole D.C. generator provided with a two layer lap winding with sixteen coils, the pole pitch will be
(a) 4
(b) 8✔
(c) 16
(d) 32

45. The material for commutator brushes is generally
(a) mica
(b) copper
(c) cast iron
(d) carbon✔

46. The insulating material used between the commutator segments is normally
(a) graphite
(b) paper
(c) mica✔
(d) insulating varnish

47. In D.C. generators, the brushes on commutator remain in contact with conductors which
(a) lie under south pole
(b) lie under north pole
(c) lie under interpolar region✔
(d) are farthest from the poles

48. If brushes of a D.C. generator are moved in order to bring these brushes in magnetic neutral axis, there will be
(a) demagnetisation only
(b) cross magnetisation as well as mag¬netisation
(c) crossmagnetisation as well as demagnetising✔
(d) cross magnetisation only

49. Armature reaction of an unsaturated D.C. machine is
(a) crossmagnetising✔
(b) demagnetising
(c) magnetising
(d) none of above

50. D.C. generators are connected to the busbars or disconnected from them only under the floating condition
(a) to avoid sudden loading of the primemover
(b) to avoid mechanicaljerk to the shaft
(c) to avoid burning of switch contacts
(d) all above✔

51. Eddy currents are induced in the pole shoes of a D.C. machine due to
(a) oscillating magnetic field
(b) pulsating magnetic flux
(c) relative rotation between field and armature✔
(d) all above

52. In a D.C. machine, short-circuited field coil will result in
(a) odour of barning insulation
(b) unbalanced magnetic pull producing vibrations
(c) reduction of generated voltage for which excitation has to be increased to maintain the voltage
(d) all above✔

53. Equilizer rings are required in case armature is
(a) wave wound
(b) lap wound✔
(c) delta wound
(d) duplex wound

54. Welding generator will have
(a) lap winding✔
(b) wave winding
(c) delta winding
(d) duplex wave winding

55. In case of D.C. machine winding, number of commutator segments is equal to
(a) number of armature coils✔
(b) number of armature coil sides
(c) number of armature conductors
(d) number of armature turns

56. For a D.C. machines laboratory following type of D.C. supply will be suitable
(a) rotary converter
(b) mercury are rectifier
(c) induction motor D.C. generator set✔
(d) synchronous motor D.C. generator set

57. The function of pole shoes in the case of D.C. machine is
(a) to reduce the reluctance of the mag¬netic path
(b) to spread out the flux to achieve uniform flux density
(c) to support the field coil
(d) to discharge all the above functions✔

58. In the case of lap winding resultant pitch is
(a) multiplication of front and back pitches
(b) division of front pitch by back pitch
(c) sum of front and back pitches
(d) difference of front and back pitches✔

59. A D.C. welding generator has
(a) lap winding✔
(b) wave moving
(c) duplex winding
(d) any of the above

60. To achieve sparkless commutation brushes of a D.C. generator are rockedm ahead so as to bring them
(a) just ahead of magnetic neutral axis✔
(b) in magnetic neutral axis
(c) just behind the magnetic neutral axis

MCQ on DC generator 21-40

21. Which of the following statement about D.C. generators is false ?
(a) Compensating winding in a D.C. machine helps in commutation
(b) In a D. C. generator interpoles winding is connected in series with the armature winding
(c) Back pitch and front pitch are both odd and approximately equal to the pole pitch
(d) Equilizing bus bars are used with parallel running of D.C. shunt generators✔

22. The demagnetising component of armature reaction in a D.C. generator
(a) reduces generator e.m.f.✔
(b) increases armature speed
(c) reduces interpoles flux density
(d) results in sparking trouble

23. Magnetic field in a D.C. generator is produced by
(a) electromagnets✔
(b) permanent magnets
(c) both (a) and (b)
(d) none of the above

24. The number of brushes in a commutator depends on
(a) speed of armature
(b) type of winding
(c) voltage
(d) amount of current to be collected✔

25. Compensating windings are used in D.C. generators
(a) mainly to reduce the eddy currents by providing local short-circuits
(b) to provide path for the circulation of cooling air
(c) to neutralise the cross-magnetising effect of the armature reaction✔
(d) none of the above

26. Which of the following components of a D.C, generator plays vital role for providing direct current of a D.C. generator ?
(a) Dummy coils
(b) Commutator✔
(c) Eye bolt
(d) Equilizer rings

27. In a D.C. generator the ripples in the direct e.m.f. generated are reduced by
(a) using conductor of annealed copper
(b) using commutator with large number of segments
(c) using carbon brushes of superior quality✔
(d) using equiliser rings

28. In D.C. generators, lap winding is used for
(a) high voltage, high current
(b) low voltage, high current✔
(c) high voltage, low current
(d) low voltage, low current

29. Two generators A and B have 6-poles each. Generator A has wave wound armature while generator B has lap wound armature. The ratio of the induced e.m.f. is generator A and B will be
(a) 2 : 3
(b) 3 : 1✔
(c) 3 : 2
(d) 1 : 3

30. The voltage drop for which of the following types of brush can be expected to be least ?
(a) Graphite brushes
(b) Carbon brushes
(c) Metal graphite brushes✔
(d) None of the above

31. The e.m.f. generated by a shunt wound D.C. generator is E. Now while pole flux remains constant, if the speed of the generator is doubled, the e.m.f. generated will be
(a) E/2
(b) 2E✔
(c) slightly less than E
(d) E

32. In a D.C. generator the actual flux distribution depends upon
(a) size of air gap
(b) shape of the pole shoe
(c) clearance between tips of the ad¬jacent pole shoes
(d) all of the above✔

33. The armature core of a D.C. generator is usually made of
(a) silicon steel✔
(b) copper
(c) non-ferrous material
(d) cast-iron

34. Satisfactory commutation of D.C. machines requires
(a) brushes should be of proper grade and size
(b) brushes should smoothly run in the holders
(c) smooth, concentric commutator properly undercut
(d) all of the above✔

35. Open circuited armature coil of a D.C. machine is
(a) identified by the scarring of the commutator segment to which open circuited coil is connected
(b) indicated by a spark completely around the commutator
(c) both (a) and (b)✔
(d) none of the above

36. For the parallel operation of two or more D.C. compound generators, we should ensure that
(a) voltage of the incoming generator should be same as that of bus bar
(b) polarity of incoming generator should be same as that of bus bar
(c) all the series fields should be run in parallel by means of equilizer connection
(d) series fields of all generators should be either on positive side or negative side of the armature✔

37. In a D.C. generator the number of mechanical degrees and electrical degrees will be the same when
(a) r.p.m. is more than 300
(b) r.p.m. is less than 300
(c) number of poles is 4
(d) number of poles is 2✔

38. Permeance is the reciprocal of
(a) flux density
(b) reluctance✔
(c) ampere-turns
(d) resistance

39. The e.m.f. generated in a D.C. generator is directly proportional to
(a) flux/pole
(b) speed of armature✔
(c) number of poles
(d) all of the above

40. In D.C. generators on no-load, the air gap flux distribution in space is
(a) sinusoidal
(b) triangular
(c) pulsating
(d) flat topped✔

MCQ on DC generator 1-20

1. Laminations of core are generally made of
(a) case iron
(b) carbon
(c) silicon steel✔
(d) stainless steel

2. Which of the following could be lamina-proximately the thickness of laminations of a D.C. machine ?
(a) 0.005 mm
(b) 0.05 mm
(c) 0.5 m✔
(d) 5 m

3. The armature of D.C. generator is laminated to
(a) reduce the bulk
(b) provide the bulk
(c) insulate the core
(d) reduce eddy current loss✔

4. The resistance of armature winding depends on
(a) length of conductor
(b) cross-sectional area of the conductor
(c) number of conductors
(d) all of the above✔

5. The field coils of D.C. generator are usually made of
(a) mica
(b) copper✔
(c) cast iron
(d) carbon

6. The commutator segments are connected to the armature conductors by means of
(a) copper lugs✔
(b) resistance wires
(c) insulation pads
(d) brazing

7. In a commutator
(a) copper is harder than mica
(b) mica and copper are equally hard
(c) mica is harder than copper✔
(d) none of the above

8. In D.C. generators the pole shoes are fastened to the pole core by
(a) rivets
(b) counter sunk screws✔
(c) brazing
(d) welding

9. According to Fleming’s right-hand rule for finding the direction of induced e.m.f., when middle finger points in the direction of induced e.m.f., forefinger will point in the direction of
(a) motion of conductor
(b) lines of force✔
(c) either of the above
(d) none of the above

10. Fleming’s right-hand rule regarding direction of induced e.m.f., correlates
(a) magnetic flux, direction of current flow and resultant force
(b) magnetic flux, direction of motion and the direction of e.m.f. induced✔
(c) magnetic field strength, induced voltage and current
(d) magnetic flux, direction of force and direction of motion of conductor

11. While applying Fleming’s right-hand rule to And the direction of induced e.m.f., the thumb points towards
(a) direction of induced e.m.f.
(b) direction of flux
(c) direction of motion of the conductor if forefinger points in the direction of generated e.m.f.
(d) direction of motion of conductor, if✔ forefinger points along the lines of flux

12. The bearings used to support the rotor shafts are generally
(a) ball bearings✔
(b) bush bearings
(c) magnetic bearmgs
(d) needle bearings

13. In D.C. generators, the cause of rapid brush wear may be
(a) severe sparking
(b) rough commutator surface
(c) imperfect contact
(d) any of the above✔

14. In lap winding, the number of brushes is always
(a) double the number of poles
(b) same as the number of poles✔
(c) half the number of poles
(d) two

15. For a D.C. generator when the number of poles and the number of armature conductors is fixed, then which winding will give the higher e.m.f. ?
(a) Lap winding
(b) Wave winding✔
(c) Either of (a) and (b) above
(d) Depends on other features of design

16. In a four-pole D.C. machine
(a) all the four poles are north poles
(b) alternate poles are north and south✔
(c) all the four poles are south poles
(d) two north poles follow two south poles

17. Copper brushes in D.C. machine are used
(a) where low voltage and high currents are involved✔
(b) where high voltage and small cur-rents are involved
(c) in both of the above cases
(d) in none of the above cases

18. A separately excited generator as compared to a self-excited generator
(a) is amenable to better voltage control
(b) is more stable
(c) has exciting current independent of load current
(d) has all above features✔

19. In case of D.C. machines, mechanical losses are primary function of
(a) current
(b) voltage
(c) speed✔
(d) none of above

20. Iron losses in a D.C. machine are independent of variations in
(a) speed
(b) load✔
(c) voltage
(d) speed and voltage