61. The chances of arc interruption in subsequent current zeros
(a) increase in case of ABCB but decrease in OCB.
(b) decrease in case of ABCB but increase in OCB.
(c) decrease in both cases.
(d) increase in both cases.
62. In a minimum oil circuit breaker the oil is used
(a) to act as circuit breaking medium only.
(b) for circuit breaking and providing insulation.
(c) for providing insulation only.
(d) for none of the above purposes.
63. The air-blast circuit breakers for 400 kV system are designed to operate in
(a) 0.1 s
(b) 0.5 s
(c) 50 ms
(d) 100 ms
64. The minimum oil circuit breaker has less volume of oil because
(a) the oil between the breaker contacts has greater strength.
(b) there is insulation between the breaker contacts.
(c) solid insulation is provided for insulating the contacts from the earth.
(d) none of the above.
65. Air used in air blast circuit breaker must
(a) be ionized.
(b) be free from moisture.
(c) have least CO2.
(d) have oil mist.
66. In air-blast circuit breaker resistance switching is used to
(a) reduce the magnitude of fault current.
(b) control the CB operating time.
(c) damp out the fast transient.
(d) change the fault current power factor.
67. SF6 gas has excellent heat transfer properties because of its
(a) low gaseous viscosity.
(b) high dielectric strength.
(c) higher molecular weight.
(d) both (a) and (b).
(e) both (a) and (c).
68. SF6 circuit breakers have the advantages of
(a) very much reduced electrical clearance, reduced moisture problem and minimum current chopping problem.
(b) noiseless operation, less arcing time resulting in less contact erosion.
(c) no reduction in dielectric strength of SF6.
(d) performance independent of ambient conditions.
(e) all of the above.
69. SF6 circuit breakers have the drawback(s) of
(a) sealing problem of gas.
(b) ingress of moisture in the gas system is dangerous.
(c) deterioration of SF6 with time.
(d) both (a) and (b).
70. Which of the following statements is not correct?
(a) SF6 is non-toxic and noninflammable gas.
(b) SF6 has very high dielectric strength roughly 24 times of that of air.
(c) SF6 is yellow in color.
(d) SF6 is about 100 times more effective than air in are extinction.
(e) SF6 has density 5 times that of air at 20°C.
71. The single most important property that makes SF6 a very efficient medium for circuit breaking is
(a) it is non-toxic and noninflammable.
(b) it has high dielectric constant.
(c) it has high breakdown strength.
(d) it is highly electronegative in character.
72. During arc extinction SF6 gas gets
(a) decomposed into SF4 and SF2.
(b) decomposed into S and F ions
(c) reduced to SF2.
73. SF6 gas is transported in
(a) air cylinders.
(b) gas cylinders.
(c) liquid form in cylinders.
(d) solid form.
74. The current chopping tendency is minimized by using SF6 gas at relatively
(a) low pressure and high viscosity.
(b) low pressure and low viscosity.
(c) high pressure and low viscosity.
(d) high pressure and high viscosity.
75. To limit current chopping in vacuum circuit breakers, the contact material employed should have the properties of
(a) low conductivity and high vapor pressure.
(b) low conductivity and low vapor pressure.
(c) high conductivity and high vapor pressure.
(d) high conductivity and low vapor pressure.
76. A thermal protection switch provides protection against
(c) short circuit.
77. For remote operation, the circuit breaker must be equipped with
(a) inverse time trip.
(b) shunt trip.
(c) time delay trip.
(d) all of these.
78. Which of the following circuit breakers is generally used in railway electrification ?
(a) Air-blast circuit breaker.
(b) Minimum oil circuit breaker.
(c) Bulk oil circuit breaker.
(d) SF6 circuit breaker.
79. What is the preferred type of CB to be installed in extra high voltage ac system ?
(a) Bulk oil type CB
(b) Air-blast CB
(c) Vacuum CB
(d) Sulphur hexafluoride (SF6) CB
80. Keeping in view the cost and overall effectiveness, the following circuit breaker is best suited for capacitor bank switching