Multiple Choice Questions of High Voltage Engineering
1. One of the main functions of personal protective grounds is to provide a _______ impedance path for a short circuit.
A) High
B) Low
C) Smooth
D) Adequate
1. (B)
2. A Safety Electrical One Line Diagram should be used to ______________ all sources of electrical energy.
A) Identify
B) Castigate
C) Evaluate
D) Modify
2. (A)
3. Work performed on an electrical system within reaching distance of energized components is________work.
A) Energized
B) Essential
C) Safe
D) Unavoidable
3. (A)
4. The Prohibited Approach Boundary is considered the same as making_____________.
A) Insulation
B) Confluence
C) Contact
D) Pastry
4. (C)
5. The minimum allowable work space around electrical equipment is ________ inches deep.
A) 36
B) 48
C) 24
D) 30
5. (D)
6. The secondary of a current transformer must never be ____________ while energized.
A) Grounded
B) Opened
C) Examined
D) Shortened
6. (B)
7. Which is the “Can’t Let Go” range of current flow?
A) 3-9 ma
B) 9-25 ma
C) 25-60 ma
D) 1-3 ma
7. (B)
8. The testing of a volt meter after a voltage test on voltage above______.
A) 120v
B) 208v
C) 277v
D) 600v
8. (D)
9. One of the three generally recognized hazards of electrical work is____.
A) Arc Flash
B) Cuts
C) Falls
D) Concussion
9. (A)
10. Gloves used for electrical protection must be electrically tested every…
A) 3 months
B) 6 months
C) 12 months
D) Never
10. (B)
11. Corona effect can be identified by
(A) Bushy sparks
(B) Faint violet glow
(C) Red light
(D) Arcing between conductors and earth.
11. (B)
12. The phenomenon of corona is generally accompanied by
(A) A bang
(B) A hissing sound
(C) Magnetic hum
(D) all of the above.
12. (B)
14. In Van de Graaff generators output voltage is controlled by
(A) Controlling the corona source voltage
(B) Controlling the belt speed
(C) Controlling the lower spray point
(D) Any of the above.
14. (A)
15. A Tesla coil is a
(A) Cascaded transformer
(B) Coreless transformer
(C) High frequency resonant transformer
(D) Low impedance transformer.
15. (C)
16. Switching surge is
(A) high voltage dc
(B) High voltage ac
(C) Short duration transient voltage
(D) Hyperbolically dying voltage.
16. (C)
17. Moles bridge is used to measure
(A) Properties of dielectric at dc
(B) Dispersion in insulation
(C) High frequency high voltages
(D) Modulation ratio frequencies.
17. (B)
18. Insulators for high voltage applications are tested for
(A) Power frequency tests
(B) Impulse tests
(C) Both (A) and (B) above
(D) None of the above.
18. (C)
19. Impulse testing of transformers is done to determine the ability of
(A) Bushings to withstand vibrations
(B) Insulation to withstand transient voltages
(C) Windings to withstand voltage fluctuations
(D) all of the above.
19. (B)
20. Transformers contribute to radio interference due to
(A) corona discharges in air
(B) Internal or partial discharges in insulation
(C) Sparking
(D) Any of the above.
20. (D)
21. As compared to air the relative dielectric strength of sulphur hexafluoride is nearly
(A) 1.5 times
(B) 2.5 times
(C) 4.0 times
(D) 5.0 times.
21. (B)
22. The electrical breakdown strength of insulating materials depends on
(A) nature of applied voltage
(B) imperfections in dielectric material
(C) pressure, temperature and humidity
(D) all of the above.
22. (D)
23. Which of the following gas has been used as insulating medium in electrical appliances ?
(A) Nitrogen
(B) Carbon dioxide
(C) Sulphur hexafluoride
(D) Freon.
23. (C)
24. Vacuum insulation is used in all of the following EXCEPT
(A) Particle accelerators
(B) EHT of color TV
(C) Field emission tubes
(D) X-rays.
24. (B)
25. Liquids are generally used as insulating materials up to voltage stresses of about
(A) 100 MV/cm
(B) 50 MV/cm
(C) 50 kV/cm
(D) 500 V/cm.
25. (C)
26. Electro-mechanical breakdown of solid insulating materials occurs due to
(A) Magnetic bum
(B) Vibrations
(C) Mechanical stresses produced by the electrical field
(D) Electrical stresses produced by the voltage fluctuations.
26. (C)
27. Surge voltage originate in power systems due to
(A) Lightning
(B) Switching operations
(C) Faults
(D) Any of the above.
27. (D)
28. All of the following are the preferred properties of a dielectric gas EXCEPT
(A) High dielectric strength
(B) Physiological inertness
(C) Low atomic number
(D) Good heat transfer.
28. (C)
29. Corona results in
(A) Improvement in power factor
(B) Increased capacitive reactance of transmission lines
(C) Radio interference
(D) Better regulation.
29. (C)
30. Which of the following technique/method is-used for the measurements of ac high frequency voltages ?
(A) Peak voltmeter
(B) Series resistance micro ammeter
(C) Resistance potential divider
(D) Any of the above.
30. (A)
31. Which of the following method or technique can be used for the measurement of high dc voltages?
(A) Generating voltmeter
(B) Electrostatic voltmeter
(C) Peak voltmeter
(D) Any of the above.
31. (A)
32. All of the following methods/techniques can be used for the measurement of high ac voltages EXCEPT
(A) Potential dividers
(B) Potential transformers
(C) Electrostatic voltmeters
(D) Half effect generators.
32. (D)
33. Surge diverters are
(A) non-linear resistors in series with spark gaps which act as fast switches
(B) arc quenching devices
(C) shunt reactors to limit the voltage rise due to Ferranti effect
(D) over-voltages of power frequency harmonics.
33. (A)
34. Impulse voltages are characterized by
(A) polarity
(B) peak value
(C) time of half the peak value
(D) all of the above.
34. (D)
35. The essential condition for the Paschen's law to be valid is that
(A) Voltage must be dc
(B) Voltage must be ac
(C) Temperature must be constant
(D) Humidity must be low.
35. (C)
36. The breakdown voltage in gases depends on
(A) distance between the electrodes
(B) relative air density
(C) humidity
(D) all of the above.
36. (D)
37. At unvarying temperature breakdown voltage in a uniform field is a function of the product of gas pressure and distance between the electrodes. The above statement is known as
(A) Electron avalanche
(B) Thermal stability principle
(C) Paschen's law
(D) Breakdown voltage law.
37. (C)
38. Large capacity generators are manufactured to generate power at
(A) 440 V
(B) 6.3 to 10.5 kV
(C) 132 kV to 220 kV
(D) 400 kV.
38. (B)
39. Which soil has the least specific resistance?
(A) Land
(B) Loamy soil
(C) Clay
(D) Peat.
39. (D)
40. Which soil has the maximum specific resistance?
(A) Black cotton soil
(B) Sand
(C) Peat
(D) Loamy soil.
40. (B)
41. In sphere gaps, the sphere are made of
(A) aluminum
(B) Brass
(C) Bronze
(D) Any of the above.
41. (D)
42. In 'plasma' state a gas
(A) Loses electrical conductivity
(B) Conducts electricity
(C) Becomes perfect insulator
(D) Attracts moisture.
42. (B)
43. Which of the following statement about corona is incorrect?
(A) Corona gives rise to radio interference
(B) Corona results in loss of power in transmission
(C) Corona discharge can be observed as red luminescence
(D) Corona is always accompanied by a hissing noise
43. (C)
44. A circuit breaker is
(A) power factor correcting device
(B) a device to neutralize the effect of transients
(C) a waveform correcting device
(D) a current interrupting device.
44. (D)
45. The function of protective relay in a circuit breaker is
(A) to each any stray voltages
(B) to close the contacts when the actuating quantity reaches a certain predetermined value
(C) to limit arcing current during the operation of circuit breaker
(D) to provide additional safety in the operation of circuit breaker.
45. (B)
46. Low voltage circuit breakers have rated voltage of less than
(A) 220 V
(B) 400V
(C) 1000 V
(D) 10,000 V.
46. (C)
47. The fault clearing time of a circuit breaker is usually
(A) few minutes
(B) few seconds
(C) one second
(D) few cycles of supply voltage.
47. (D)
48. The medium employed for extinction of arc in air circuit breaker is
(A) SF6
(B) Oil
(C) Air
(D) Water.
48. (C)
49. Which of the following circuit breakers is preferred for EHT application
(A) Air blast circuit breakers
(B) Minimum oil circuit breakers
(C) Bulk oil circuit breakers
(D) SF6 oil circuit breakers.
49. (D)
50. For high voltage, ac circuit breakers, the rated short circuit current is passed for
(A) 0.01 sec
(B) 0.1 sec
(C) 3 seconds
(D) 30 seconds.
50. (C)
51. Which of the following is not a type of the contactor for circuit breakers ?
(A) Electro-magnetic
(B) Electro-pneumatic
(C) Pneumatic
(D) Vacuum.
51. (D)
52. Interrupting medium in a contactor may be
(A) air
(B) oil
(C) SF6 gas
(D) any of the above.
52. (D)
53. In air blast circuit breakers, the pressure of air is of the order of
(A) 100 mm Hg
(B) 1 kg/cm2
(C) 20 to 30 kg/cm2
(D) 200 to 300 kg/cm2 .
53. (C)
54. SF6 gas is
(A) sulphur fluoride
(B) sulphur difluoride
(C) sulphur hexafluorine
(D) sulphur hexafluoride.
54. (D)
55. SF6 gas
(A) is yellow in color
(B) has pungent odor
(C) is highly toxic
(D) is non-inflammable.
55. (D)
56. SF6 gas
(A) is lighter than hydrogen
(B) is lighter than air
(C) has density 2-times as compared to that of air
(D) has density 5 limes as compared to that of air.
56. (D)
57. The pressure of SF6 gas in circuit breakers is of the order of
(A) 100 mm Hg
(B) 1 kg/cm2
(C) 3 to 5 kg/cm2
(D) 30 to 50 kg/cm2.
57. (C)
58. While selecting a gas for circuit breaker, the property of gas that should be considered is
(A) high dielectric strength
(B) non-inflammability
(C) non-toxicity
(D) all of the above.
58. (D)
59. Out of the following circuit breakers, which one has the lowest voltage range ?
(A) Air-break circuit breaker
(B) Tank type oil circuit breaker
(C) Air-blast circuit breaker
(D) SF6 circuit breaker.
59. (A)
60. Which of the following circuit breaker can be installed on 400 kV line
(A) Tank type oil circuit breaker
(B) Miniature circuit breaker
(C) Vacuum circuit breaker
(D) Air blast circuit breaker.
60. (D)
61. In a vacuum circuit breaker, the vacuum is of the order of
(A) 10mm Hg
(B)10-2mmHg
(C) l0-6 mmHg
(D)10-9mmHg.
61. (D)
62. In modem EHV circuit breakers, the operating time between instant of receiving trip signal and final contact separation is, of the order of
(A) 0.001 sec
(B) 0.015 sec
(C) 0.003 sec
(D) 0.03 sec.
62. (D)
63. In a HRC fuse the time between cut-off and final current zero, is known as
(A) total operating time
(B) arcing time
(C) pre-arcing time
(D) any of the above.
63. (B)
64. Fusing factor for a HRC fuse is
(A) Minimum fusing current / Current rating
(B) Minimum fusing current / Minimum rupturing time
(C) Maximum fusing current / Minimum fusing current
(D) Minimum fusing current / Prospective current of circuit.
64. (A)
65. Which of the following circuit breakers does not use pneumatic operating mechanism?
(A) Air blast circuit breaker
(B) SF6 blast circuit breaker
(C) Air break circuit breaker
(D) Bulk-oil circuit breaker.
65. (D)
66. The contact resistance of a circuit breaker is. of the order of
(A) 20 micro ohms ± 10
(B) 20milli ohms ± 10
(C) 20 ohms ± 10
(D) 200 ohms ± 10.
66. (A)
67. The insulation resistance of high voltage circuit breaker is
(A) 1k Ohm (B) 10 k Ohm (C) 20 Mega ohms (D) 2000 Mega ohm.
67. (D)
68. There is definite objection to use of which of the following medium for extinguishing the arc in case of a circuit breaker ?
(A) Air
(B) SF6 gas
(C) Vacuum
(D) Water.
68. (D)
69. In a circuit breaker if the insulation resistance between phase terminal and earthed frame is less than the specified limit, the probable cause could be
(A) moisture
(B) dirty insulation surface
(C) carbon or copper particles sticking to the internal surface
(D) any of the above.
69. (D)
70. If a circuit breaker does not operate on electrical compound, the probable reason could be
(A) spring defective (B) trip circuit open (C) trip latch defective (D) any of the above.
70. (D)
71. The normal frequency rms voltage that appears across the breaker poles after final arc extinction has occurred, is
(A) recovery voltage (B) re striking voltage (C) supply voltage (D) peak voltage.
71. (A)
72. The transient voltage that appears across the contacts at the instant of arc extinction is called
(A) recovery voltage (B) re striking voltage (C) supply voltage (D) peak voltage.
72. (B)
73. In a circuit breaker the active recovery voltage depends upon
(A) power factor (B) armature reaction (C) circuit conditions (D) all of the above.
73. (D)
74. The following figure shows the voltage waveform across the pole of a circuit breaker; In this voltage R represents
(A) System voltage (B) Re striking voltage (C) Recovery voltage (D) Extinction of arc.
74. (B)
75. In the above figure, D represents
(A) Recovery voltage
(B) Re striking voltage
(C) System voltage
(D) Extinction of arc.
75. (A)
76. Best protection is provided by HRC fuses in case of
(A) Open circuits
(B) Short circuits
(C) Overloads
(D) None of the above.
76. (B)
77. For motor circuit breakers, the time of closing the cycle is
(A) 0.001 sec
(B) 0.01 sec
(C) 0.10 sec
(D) 0.003 sec.
77. (D)
78. A relay used for protection of motors against overload is
(A) Impedance relay
(B) Electromagnetic attraction type
(C) Thermal relay
(D) Buchholz's relay.
78. (C)
79. Which curve in the figure represents inverse time characteristics ?
(A) Curve A
(B) Curve B
(C) Curve C
(D) Curve D.
79. (A)
80. Fuse protection is used for current ratings up to
(A) 10 A
(B) 20 A
(C) 50 A
(D) 100 A.
80. (D)
81. The fuse current in amperes is related with fuse wire diameter D as
(A) I ∞ I/D
(B) I ∞ D
(C) I ∞ D3/2
(D) I ∞ D2.
81. (C)
82. The acting contacts for a circuit breakers are made of
(A) Stainless steel
(B) Hard pressed carbon
(C) Porcelain
(D) Copper tungsten alloy.
82. (D)
83. Ionization in a circuit breaker is not facilitated by
(A) High temperature of surrounding medium
(B) material of contacts
(C) increase of field strength
(D) increase of mean free path.
83. (B)
84. Which circuit breaker is generally used in railway traction ?
(A) SF6 gas circuit breaker
(B) Air break circuit breaker
(C) Vacuum circuit breaker
(D) Minimum oil circuit breaker.
84. (B)
85. A fuse wire should have
(A) Low specific resistance and high melting point
(B) Low specific resistance and low melting point
(C) High specific resistance and high melting point
(D) High specific resistance and low melting point.
85. (D)
86. Fuse wire, protection, system is usually not used beyond
(A) 10 A
(B) 25 A
(C) 50 A
(D)100A.
86. (D)
87. For extra high voltage lines which circuit breaker is preferred
(A) Bulk oil circuit breaker
(B) Vacuum circuit breaker
(C) SF6 gas circuit breaker
(D) Minimum oil circuit breaker.
87. (C)
88. The number of cycles in which a high speed circuit breaker can complete its operation is
(A) 3 to 8
(B) 10 to 18
(C) 20 to 30
(D) 40 to 50.
88. (A)
89. When D is the diameter of fuse wire, the fusing current will be proportional to
(A) 1/D
(B) 1/D2
(C) D3/2
(D) D1/2
89. (C)
90. A material best suited for manufacturing of fuse wire is
(A) Aluminium
(B) Silver
(C) Lead
(D) Copper.
90. (B)
91. In a circuit breaker the current which exists at the instant of contact separation is known as
(A) Re striking current (B) Surge current (C) breaking current (D) Recovery current.
91. (C)
92. A Merz-price protection is suitable for
(A) Transformers (B) Alternators (C) Feeders (D) Transmission lines.
92. (B)
93. 'Kick fuse' has
(A) square law characteristics (B) linear characteristics (C) inverse characteristics.
93. (C)
94. Air blast circuit breakers for 400 kV. Power system are designed to operate in
(A) 50 micro seconds (B) 50 milli seconds (C) 500 milli seconds (D) 50 seconds.
94. (B)
95. Breaking capacity of a circuit breaker is usually expressed in terms of
(A) Amperes (B) Volts (C) MW (D) MVA.
95. (D)
96. Sulphur hexafluoride is a
(A) Conductor of electricity (B) Semi-conductor (C) Inactive gas (D) Dielectric.
96. (D)
97. The contact resistance is least affected by
(A) The mechanical force applied
(B) The shape of the contact faces
(C) the amount of surface contamination
(D) The ambient temperature.
97. (D)
98. The arc voltage produced in ac circuit breaker is
(A) leading the arc current by 90°
(B) lagging the arc current by 90°
(C) In phase with the arc current
(D) In phase opposition to the arc current.
98. (C)
Questions 99 to 102 refer to the following figure :
99. Various forms of contacts are shown in the figure above. Point contact is (are) represented by
(A) A only
(B) A and B only
(C) A, B and C only
(D) A, B, C and D.
99. (B)
100. Which contact surface provides line contact only?
(A) A
(B) B
(C) C
(D) D.
100. (C)
101. Which form of contact are widely used in switchgear particle ?
(A) A and B only
(B) A and C only
(C) C and D only
(D) B, C and D only.
101. (C)
102. For the various types of contacts Shown, for the same force, F, the contact resistance will be least in case of
(A) A
(B) B
(C) C
(D) D.
102. (A)
103. As the force on contact is increased, the contact resistance will
(A) Increase linearly
(B) Increase exponentially
(C) Remain unaltered
(D) Decrease.
103. (D)
104. The heat produced at the contact point, due to passage of current, will least depend on
(A) Contact resistance
(B) Time during which the current flows
(C) Current flowing
(D) Temperature of the surrounding medium.
104. (D)
105. For the contact and their material, which of the following should have low value
(A) Contact resistance (B) Thermal capacity (C) Thermal conductivity (D) All of the above.
105. (A)
106. Minimum arcing voltage will be least in case of
(A) Carbon (B) Graphite (C) Tungsten (D) Silver.
106. (D)
107. Minimum arcing voltage for platinum is 16 V. It can be therefore concluded that when the voltage is below 16 V
(A) it will not be possible to interrupt the circuit
(B) it will not be possible to pass the current
(C) it will be possible to interrupt any value of current without arcing
(D) it will be possible to interrupt any value of current without bringing contact closer to one another.
107. (C)
108. Oil immersion of contacts is the method of
(A) arc dispersion (B) arc prevention (C) de ionization (D) none of the above.
108. (A)
109. Which of the following is not the method of arc dispersion ?
(A) Oil immersion of contacts (B) Magnetic blow out of arc (C) Use of rectifiers (D) De ionization of arc path.
109. (C)
