Electrical Interview Questions Set- 4
(a) 30°
(b) 60°
(c) 90°
(d) 180°
Ans: c
2. 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
Ans: d
3. 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
Ans: b
4. Synchronsizingpower of a synchronous machine is
(a) direcly proportional to the synchronous reactance
(6) inversely proportional to the synchronous reactance
(a) equal to the synchronous reactance
(d) none of the above
Ans: b
5. Synchronous motors are
(a) not-self starting
(b) self-starting
(c) essentially self-starting
(d) none of the above
Ans: a
6. 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
Ans: c
7. 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
Ans: b
8. 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
Ans: b
9. A synchronous motor working at leading power factor can be used as
(a) voltage booster
(b) phase advancer
(c) noise generator
(d) mechanical synchronizer
Ans: b
10. Slip rings are usually made of
(a) carbon or graphite
(b) brass or steel
(c) silver or gold
(d) copper or aluminium
Ans: b
11. An over excited synchronous motor is used for
(a) fluctuating loads
(b) variable speed loads
(c) low torque loads
(d) power factor corrections
Ans: d
12. 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
Ans: d
13. 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%
Ans: c
14. To limit the operating temperature an electrical machine should have proper
(a) voltage rating
(b) current rating
(c) power factor
(d) speed
Ans: b
15. Slip-rings in a synchronous motor carry
(a) direct current
(b) alternating current
(c) no current
(d) all of the above
Ans: a
16. 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
Ans: d
17. 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
Ans: c
18. 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
(e) nine times
Ans: c
19. The angle between the rotating stator flux and rotor poles is called _____ angle.
(a) torque
(b) obtuse
(c) synchronizing
(d) power factor
Ans: a
20. 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
Ans: c
21. 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
(e) none of the above
Ans: b
22. 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
Ans: a
23. 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
Ans: c
24. 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
Ans: b
25. 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
(e) all of the above
Ans: c
26. 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
Ans: b
27. 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
Ans: d
28. 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
Ans: b
29. 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
Ans: c
30. 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 faces
(d) reHetance motor torque due to saliency of the rotor
(e) all of the above methods
Ans: e
31. 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
Ans: d
32. 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.
Ans: a
33. 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
Ans: b
34. 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
Ans: b
35. 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
Ans: a
36. 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.
Ans: b
37. 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
(e) none of the above
Ans: d
38. 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
Ans: a
39. 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
Ans: b
40. 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
Ans: d
41. 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
Ans: c
42. 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
43. The maximum speed variation in a 3-phase synchronous motor is
(a) 10 per cent
(b) 6 per cent
(c) 4 per cent
(d) 2. per cent
(e) zero
Ans: e
44. 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
Ans: d
45. 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
Ans: d
46. 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
Ans: c
47. 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
Ans: a
48. In a synchronous motor, damper windings are provided on
(a) stator frame
(b) rotor shaft
(c) pole faces
(d) none of the above
Ans: c
49. 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
Ans: a
50. The effect of increasing the load on a synchronous motor running with normal
excitation is to
(a) decrease both armature current and power factor
(6) decrease armature current but increase power factor
(c) increase armature current but decrease power factor
(d) increase both its armature current and power factor
Ans: c
51. 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
Ans: d
52. The ratio of starting torque to running torque in a synchronous motor is
(a) zero
(b) one
(c) two
(d) infinity
Ans: a
53. 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
Ans: b
54. 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
(e) none of the above
Ans: b
55. 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
Ans: a
56. 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
Ans: c
57. Hunting in a synchronous motor cannot be due to
(a) windage friction
(b) variable load
(c) variable frequency
(d) variable supply voltage
Ans: a
58. 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.
Ans: a
59. 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
Ans: a
60. 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
Ans: b
61. A synchronous motor connected to infinite bus-bars has at constant full load, 100%
excitation and unity power fac
tor. 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
Ans: d
62. 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
Ans: b
63. 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
Ans: d
64. 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
Ans: a
65. If the field of a synchronous motor is underexcited, the power factor will be
(a) zero
(b) unity
(c) lagging
(d) leading
Ans: c
66. The back e.m.f. in the stator of a synchronous motor depends on
(a) number of poles
(b) flux density
(c) rotor speed
(d) rotor excitation
(e) none of the above
Ans: d
67. 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
Ans: d
68. 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
Ans: c
69. 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
Ans: a
70. 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
Ans: a
71. 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
(e) None of the above
Ans: d
72. 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
Ans: c
73. 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
Ans: b
74. 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
Ans: a
75. The construction of a synchronous motor resembles
(a) a series motor
(b) an induction motor
(c) an alternator
(d) a rotary converter
Ans: c
76. 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
Ans: a
77. 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
Ans: a
78. 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
Ans: a
79. 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
Ans: a
80. 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
Ans: b
81. 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
Ans: a
82. 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
Ans: c
83. 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°)
(e) none of the above
Ans: d
84. 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
Ans: c
85. A synchronous motor develops maximum power when load angle is
(a) 45°
(b) 60°
(c) 90°
(d) 120°
Ans: c
86. 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
Ans: a
87. By which of the following systems electric power may be transmitted ?
(a) Overhead system
(b) Underground system
(c) Both (a) and (b)
(d) None of the above
Ans: c
88. are the conductors, which connect the consumer's terminals to the distribution
(a) Distributors
(b) Service mains
(c) Feeders
(d) None of the above
Ans: b
89. The underground system cannot be operated above
(a) 440 V
(b) 11 kV
(c) 33 kV
(d) 66 kV
Ans: d
90. Overhead system can be designed for operation upto
(a) 11 kV
(b) 33 kV
(c) 66 kV
(d) 400 kV
Ans: c
91. If variable part of annual cost on account of interest and depreciation on the capital
outlay is equal to the
annual cost of electrical energy wasted in the conductors, the total annual cost will be
minimum and the corresponding size of conductor will be most economical. This statement
is known as
(a) Kelvin's law
(b) Ohm's law
(c) Kirchhoffs law
(d) Faraday's law
(e) none of the above
Ans: a
92. The wooden poles well impregnated with creosite oil or any preservative compound
have life
(a) from 2 to 5 years
(b) 10 to 15 years
(c) 25 to 30 years
(d) 60 to 70 years
Ans: c
93. Which of the following materials is not used for transmission and distribution of
electrical power ?
(a) Copper
(b) Aluminium
(c) Steel
(d) Tungsten
Ans: d
94. Galvanised steel wire is generally used as
(a) stay wire
(b) earth wire
(c) structural components
(d) all of the above
Ans: d
95. The usual spans with R.C.C. poles are
(a) 40—50 metres
(b) 60—100 metres
(c) 80—100 metres
(d) 300—500 metres
Ans: c
96. The corona is considerably affected by which of the following ?
(a) Size of the conductor
(b) Shape of the conductor
(c) Surface condition of the conductor
(d) All of the above
Ans: d
97. Which of the following are the constants of the transmission lines ?
(a) Resistance
(b) Inductance
(c) Capacitance
(d) All of the above
Ans: d
98. 310 km line is considered as
(a) a long line
(b) a medium line
(c) a short line
(d) any of the above
Ans: a
99. The phenomenon qf rise in voltage at the receiving end of the open-circuited or lightly
loaded line is called the
(a) Seeback effect
(b) Ferranti effect
(c) Raman effect
(d) none of the above
Ans: b
100. The square root of the ratio of line impedance and shunt admittance is called the
(a) surge impedance of the line
(b) conductance of the line
(c) regulation of the line
(d) none of the above
Ans: a
101. Which of the following is the demerit of a 'constant voltage transmission system' ?
(a) Increase of short-circuit current of the system
(b) Availability of steady voltage at all loads at the line terminals
(c) Possibility of better protection for the line due to possible use of higher terminal
reactances
(d) Improvement of power factor at times of moderate and heavy loads
(e) Possibility of carrying increased power for a given conductor size in case of long- distance heavy power
transmission
Ans: a
102. Low voltage cables are meant for use up to
(a)l.lkV
(b)3.3kV
(c)6.6kV
(d)llkV
Ans: e
103. The operating voltage of high voltage cables is upto
(a)l.lkV
(b)3.3kV
(c)6.6kV
(d)llkV
Ans: d
104. The operating voltage of supertension cables is upto
(a) 3.3 kV
(b) 6.6 kV
(c) 11 kV
(d) 33 kV
Ans: d
105. The operating voltage of extra high tension cables is upto
(a) 6.6 kV
(b) 11 kV
(c) 33 kV
(d) 66 kV
(e) 132 kV
Ans: d
106. Which of the following methods is used for laying of underground cables ?
(a) Direct laying
(b) Draw-in-system
(c) Solid system
(d) All of the above
Ans: d
107. Which of the following is the source of heat generation in the cables ?
(a) Dielectric losses in cable insulation
(b) losses in the conductor
(c) Losses in the metallic sheathings and armourings
(d) All of the above
Ans:
108. Due to which of the following reasons the cables should not be operated too hot ?
(a) The oil may loose its viscosity and it may start drawing off from higher levels
(b) Expansion of the oil may cause the sheath to burst
(c) Unequal expansion may create voids in the insulation which will lead to ionization
(d) The thermal instability may rise due to the rapid increase of dielectric losses with
temperature
(e) All of the above
Ans: e
109. Which of the following D.C. distribution system is the simplest and lowest in first cost
?
(a) Radial system
(b) Ring system
(c) Inter-connected system
(d) None of the above
Ans: a
110. A booster is a
(a) series wound generator
(b) shunt wound generator
(c) synchronous generator
(d) none of the above
Ans: a
111. Besides a method of trial and error, which of the following methods is employed for
solution of network problems
in interconnected system ?
(a) Circulating current method
(b) Thevenin's theorem
(c) Superposition of currents
(d) Direct application of Kirehhoffs laws
(e) All of the above
Ans: e
112. Which of the following faults is most likely to occur in cables ?
(a) Cross or short-circuit fault
(b) Open circuit fault
(c) Breakdown of cable insulation
(d) All of the above
Ans: d
113. The cause of damage to the lead sheath of a cable is
(a) crystallisation of the lead through vibration
(b) chemical action on the lead when buried in the earth
(c) mechanical damage
(d) all of the above
Ans: d
114. The voltage of the single phase supply to residential consumers is
(a) 110 V
(b) 210 V
(c) 230 V
(d) 400 V
Ans: c
115. Most of the high voltage transmission lines in India are
(a) underground
(b) overhead
(c) either of the above
(d) none of the above
Ans: b
116. The distributors for residential areas are
(a) single phase
(b) three-phase three wire
(c) three-phase four wire
(d) none of the above
Ans: c
117. The conductors of the overhead lines are
(a) solid
(b) stranded
(c) both solid and stranded
(d) none of the above
Ans: b
118. High voltage transmission lines use
(a) suspension insulators
(b) pin insulators
(c) both (a) and (b)
(d) none of the above
Ans: a
119. Multicore cables generally use
(a) square conductors
(b) circular conductors
(c) rectangular conductors
(d) sector-shaped conductors
(e) none of the above
Ans: d
120. Distribution lines in India generally use
(a) wooden poles
(b) R.C.C. poles
(c) steel towers
(d) none of the above
Ans: b
121. The material commonly used for insulation in high voltage cables is
(a) lead
(b) paper
(c) rubber
(d) none of the above
Ans: b
122. The loads on distributors systems are generally
(a) balanced
(b) unbalanced
(c) either of the above
(d) none of the above
Ans: b
123. The power factor of industrial loads is generally
(a) unity
(b) lagging
(c) leading
(d) zero
Ans: b
124. Overhead lines generally use
(a) copper conductors
(b) all aluminium conductors
(c) A.C.S.R. conductors
(d) none of these
Ans: c
125. In transmission lines the cross-arms are made of
(a) copper
(b) wood
(c) R.C.C.
(d) steel
Ans: d
126. The material generally used for armour of high voltage cables is
(a) aluminium
(b) steel
(c) brass
(d) copper
Ans: b
127. Transmission line insulators are made of
(a) glass
(b) porcelain
(c) iron
(d) P.V.C.
Ans: b
128. The material commonly used for sheaths of underground cables is
(a) lead
(b) rubber
(c) copper
(d) iron
Ans: a
129. The minimum clearance between the ground and a 220 kV line is about
(a) 4.3 m
(b) 5.5 m
(c) 7.0 m
(d) 10.5 m
Ans: c
130. The spacing between phase conductors of a 220 kV line is approximately equal to
(a) 2 m
(b) 3.5 m
(c) 6 m
(d) 8.5 m
Ans: c
131. Large industrial consumers are supplied electrical energy at
(a) 400 V
(b) 11 kV
(c) 66 kV
(d) 400 kV
Ans: c
132. In a D.C. 3-wire distribution system, balancer fields are cross-connected in order to
(a) boost the generated voltage
(b) balance loads on both sides of the neutral
(c) make both machine^ run as unloaded motors
(d) equalize voltages on the positive and negative outers
Ans: d
133. In a D.C. 3-wire distributor using balancers and having unequal loads on the two sides
(a) both balancers run as generators
(b) both balancers run as motors
(c) balancer connected to lightly- loaded side runs as a motor
(d) balancer connected to heavily- loaded side runs as a motor
Ans: c
134. Transmitted power remaining the same, if supply voltage of a D.C. 2-wire feeder is
increased 100 percent, saving in copper is
(a) 25 percent
(b) 50 percent
(c) 75 percent
(d) 100 percent
Ans: b
135. A uniformly-loaded D.C. distributor is fed at both ends with equal voltages. As
compared to a similar distributor fed at one end only, the drop at the middle point is
(a) one-fourth
(b) one-third
(c) one-half
(d) twice
(e) none of the above
Ans: a
136. As compared to a 2-wire D.C. distributor, a 3-wire distributor with same maximum
voltage to earth uses only
(a) 31.25 percent of copper
(b) 33.3 percent of copper
(c) 66.7 percent of copper
(d) 125 percent of copper
Ans: a
137. Which of the following is usually not the generating voltage ?
(a) 6.6 kV
(b) 8.8 kV
(c) 11 kV
(d) 13.2 kV
Ans: b
138. For an overhead line, the surge impedance is taken as
(a) 20-30 ohms
(b) 70—80 ohms
(c) 100—200 ohms
(d) 500—1000 ohms
(e) none of the above
Ans: c
139. The presence of ozone due to corona is harmful because it
(a) reduces power factor
(b) corrodes the material
(c) gives odour
(d) transfer energy to the ground
(e) none of the above
Ans: b
140. A feeder, in a transmission system, feeds power to
(a) distributors
(b) generating stations
(c) service mains
(d) all of the above
Ans: a
141. The power transmitted will be maximum when
(a) corona losses are minimum
(b) reactance is high
(c) sending end voltage is more
(d) receiving end voltage is more
Ans: c
142. A 3-phase 4 wire system is commonly used on
(a) primary transmission
(b) secondary transmission
(c) primary distribution
(d) secondary distribution
Ans: d
143. Which of the following materials is used for overhead transmission lines ?
(a) Steel cored aluminium
(b) Galvanised steel
(c) Cadmium copper
(d) Any of the above
Ans: d
144. Which of the following is not a constituent for making porcelain insulators ?
(a) Quartz
(b) Kaolin
(c) Felspar
(d) Silica
Ans: d
145. There is a greater possibility of occurence of corona during
(a) dry weather
(b) winter
(c) summer heat
(d) humid weather
(e) none of the above
Ans: d
146. Which of the following relays is used on long transmission lines ?
(a) Impedance relay
(b) Mho's relay
(c) Reactance relay
(d) None of the above
Ans: b
147. The steel used in steel cored conductors is usually
(a) alloy steel
(b) stainless steel
(c) mild steel
(d) high speed steel
(e) all of the above
Ans: c
148. Which of the following distribution systems is more reliable ?
(a) Radial system
(b) Tree system
(c) Ring main system
(d) All are equally reliable
Ans: c
149. Which of the following characteristics should the line supports for transmission lines
possess ?
(a) Low cost
(b) High mechanical strength
(c) Longer life
(d) All of the above
Ans: d
150. Transmission voltage of llkV is normally used for distances upto
(a) 20—25 km
(b) 40—50 km
(c) 60—70 km
(d) 80—100 km
Ans: a
151. Which of the following regulations is considered best?
(a) 50%
(b) 20%
(c) 10%
(d) 2%
Ans: d
152. Skin effect is proportional to
(a) (conductor diameter)
(b) (conductor diameter)
(c) (conductor diameter)
(d) (conductor diameter)
(e) none of the above
Ans: c
153. A conductor, due to sag between two supports, takes the form of
(a) semi-circle
(b) triangle
(c) ellipse
(d) catenary
Ans: d
154. In AC.S.R. conductors, the insulation between aluminium and steel conductors is
(a) insulin
(b) bitumen
(c) varnish
(d) no insulation is required
Ans: d
155. Which of the followingbus-bar schemes has the lowest cost ?
(a) Ring bus-bar scheme
(b) Single bus-bar scheme
(c) Breaker and a half scheme
(d) Main and transfer scheme
Ans: b
156. Owing to skin effect
(a) current flows through the half cross-section of the conductor
(b) portion of the conductor near the surface carries more current and core of the
conductor carries less current
(c) portion of the conductor near the surface carries less current and core of the conductor
carries more current
(d) any of the above
(e) none of the above
Ans: b
157. By which of the following methods string efficiency can be improved ?
(a) Using a guard ring
(b) Grading the insulator
(c) Using long cross arm
(d) Any of the above
(e) None of the above
Ans: d
158. In aluminium conductors, steelcore is provided to
(a) compensate for skin effect
(b) neutralise proximity effect
(c) reduce line inductance
(d) increase the tensile strength
Ans: d
159. By which of the following a bus-bar is rated ?
(a) Current only
(b) Current and voltage
(c) Current, voltage and frequency
(d) Current, voltage, frequency and short time current
Ans: d
160. A circuit is disconnected by isolators when
(a) line is energized
(b) there is no current in the line
(c) line is on full load
(d) circuit breaker is not open
Ans: b
161. For which of the following equipment current rating is not necessary ?
(a) Circuit breakers
(b) Isolators
(c) Load break switch
(d) Circuit breakers and load break switches
Ans: b
162. In a substation the following equipment is not installed
(a) exciters
(b) series capacitors
(c) shunt reactors
(d) voltatre transformers
Ans: a
163. jCorona usually occurs when the electrostatic stress in air around the conductor
exceeds
(a) 6.6 kV (r.m.s. value)/cm
(b) 11 kV (r.m.s. value)/cm
(c) 22 kV (maximum value)/cm
(d) 30 kV (maximum v^lue)/cm
Ans: d
164. The voltage drop, for constant voltage transmission is compensated by installing
(a) inductors
(b) capacitors
(c) synchronous motors
(d) all of above
(e) none of the above
Ans: c
165. The use of strain type insulators is made where the conductors are
(a) dead ended
(b) at intermediate anchor towers
(c) any of the above
(d) none of the above
Ans: c
166. The current drawn by the line due to corona losses is
(a) non-sinusoidal
(b) sinusoidal
(c) triangular
(d) square
Ans: a
167. Pin type insulators are generally not used for voltages beyond
(a) 1 kV
(b) 11 kV
(c) 22 kV
(d) 33 kV
Ans: d
168. Aluminium has a specific gravity of
(a) 1.5
(b) 2.7
(c) 4.2
(d) 7.8
Ans: b
169. For transmission of power over a distance of 200 km, the transmission voltage should
be
(a) 132 kV
(b) 66 kV
(c) 33 kV
(d) 11 kV
Ans: a
170. For aluminium, as compared to copper, all the following factors have higher values
except
(a) specific volume
(6) electrical conductivity
(c) co-efficient of linear expansion
(d) resistance per unit length for same cross-section
Ans: b
171. Which of the following equipment, for regulating the voltage in distribution feeder,
will be most economical ?
(a) Static condenser
(b) Synchronous condenser
(c) Tap changing transformer
(d) Booster transformer
Ans: d
172. In a tap changing transformer, the tappings are provided on
(a) primary winding
(b) secondary winding
(c) high voltage winding
(d) any of the above
Ans: b
173. Constant voltage transmission entails the following disadvantage
(a) large conductor area is required for same power transmission
(b) short-circuit current of the system is increased
(c) either of the above
(d) none of the above
Ans: b
174. On which of the following factors skin effect depends ?
(a) Frequency of the current
(b) Size of the conductor
(c) Resistivity of the conductor material
(d) All of the above
Ans: d
175. The effect of corona can be detected by
(a) presence of zone detected by odour
(b) hissing sound
(c) faint luminous glow of bluish colour
(d) all of the above
Ans: d
176. For transmission of power over a distance of 500 km, the transmission voltage should
be in the range
(a) 150 to 220 kV
(b) 100 to 120 kV
(c) 60 to 100 kV
(d) 20 to 50 kV
Ans: a
177. In the analysis of which of the following lines shunt capacitance is neglected ?
(a) Short transmission lines
(b) Medium transmission lines
(c) Long transmission lines
(d) Medium as well as long transmission lines
Ans: a
178. When the interconnector between two stations has large reactance
(a) the transfer of power will take place with voltage fluctuation and noise
(b) the transfer of power will take place with least loss
(c) the stations will fall out of step because of large angular displacement between the
stations
(d) none of the above
Ans: c
179. The frequency of voltage generated, in case of generators, can be increased by
(a) using reactors
(b) increasing the load
(c) adjusting the governor
(d) reducing the terminal voltage
(e) none of the above
Ans: c
180. When an alternator connected to the bus-bar is shut down the bus-bar voltage will
(a) fall
(b) rise
(c) remain unchanged
(d) none of the above
Ans: c
181. The angular displacement between two interconnected stations is mainly due to
(a) armature reactance of both alternators
(b) reactance of the interconnector
(c) synchronous reactance of both the alternators
(d) all of the above
Ans: a
182. Electro-mechanical voltage regulators are generally used in
(a) reactors
(b) generators
(c) transformers
(d) all of the above
Ans: b
183. Series capacitors on transmission lines are of little use when the load VAR
requirement is
(a) large
(b) small
(b) fluctuating
(d) any of the above
Ans: b
184. The voltage regulation in magnetic amplifier type voltage regulator is effected by
(a) electromagnetic induction
(b) varying the resistance
(c) varying the reactance
(d) variable transformer
Ans: c
185. When a conductor carries more current on the surface as compared to core, it is due
to
(a) permeability variation
(b) corona
(c) skin effect
(d) unsymmetrical fault
(e) none of the above
Ans: c
186. The following system is not generally used
(a) 1-phase 3 wire
(b) 1-phase 4 wire
(c) 3-phase 3 wire
(d) 3-phase 4 wire
Ans: a
187. The skin effect of a conductor will reduce as the
(a) resistivity of conductor material increases
(b) permeability of conductor material increases
(c) diameter increases
(d) frequency increases
Ans: a
188. When a live conductor of public electric supply breaks down and touches the earth
which of the following will happen ?
(a) Current will flow to earth
(b) Supply voltage will drop
(c) Supply voltage will increase
(d) No current will flow in the conductor
(e) None of the above
Ans: a
189. The insulating material for a cable should have
(a) low cost
(b) high dielectric strength
(c) high mechanical strength
(d) all of the above
Ans: d
190. Which of the following protects a cable against mechanical injury ?
(a) Bedding
(b) Sheath
(c) Armouring
(d) None of the above
Ans: c
191. Which of the following insulation is used in cables ?
(a) Varnished cambric
(b) Rubber
(c) Paper
(d) Any of the above
Ans: d
192. Empire tape is
(a) varnished cambric
(b) vulcanised rubber
(c) impregnated paper
(d) none of the above
Ans: a
193. The thickness of the layer of insulation on the conductor, in cables, depends upon
(a) reactive power
(b) power factor
(c) voltage
(d) current carrying capacity
Ans: c
195. The bedding on a cable consists of
(a) hessian cloth
(b) jute
(c) any of the above
(d) none of the above
Ans: c
196. The insulating material for cables should
(a) be acid proof
(b) be non-inflammable
(c) be non-hygroscopic
(d) have all above properties
Ans: d
197. In a cable immediately above metallic sheath _____ is provided.
(a) earthing connection
(b) bedding
(c) armouring
(d) none of the above
Ans: b
198. The current carrying capacity of cables in D.C. is more thanthat in A.C. mainly due to
(a) absence of harmonics
(b) non-existence of any stability limit
(c) smaller dielectric loss
(d) absence of ripples
(e) none of the above
Ans: c
200. In case of three core flexible cable the colour of the neutral is
(a) blue
(b) black
(c) brown
(d) none of the above
Ans: a
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