# Power systems MCQs Gate Preparation Power Transmission Generation-4

76.If the excitation of the synchronous generator fails, it acts as a
a) synchronous motor
b) synchronous generator
c)induction motor
d)induction generator

77.A power system network with the capacity at 100 MVA has a source impedance at 10% at a point. The fault at that point is
a)10 MVA b)30 MVA
c)3000 MVA d)1000MVA

78.Four identical alternators each rated for 20 MVA,11 KV having a sub-transient reactance of 16% are working in parallel. The short-circuit level at the bus bars is
a)500 MVA b)400 MVA
c)125 MVA d)80 MVA

79.When a line-to-ground fault occurs, the current in the phase is 100 Althea zero sequence current in this case will be
a) zero b)33.3 A
c)66.6 A d)100 A

80.Zero sequence currents can flow from a line into a transformer bank if the windings are in
a) ground star/delta
b) delta/star
c)star/grounded star
d)delta/delta

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81.In a power system with negligible resistance, the fault current at a point is 8.00 p.u.the series reactance to be included at the fault point to limit the short-circuit current to 5.00 p.u. is
a)3.000 p.u. b)0.200 p.u
c)0.125 p.u d)0.075 p.u

82. Capacitance-voltage transformer (CVT)is used to
a)improve the power factor of the transmission
b)reduce losses in a transmission line
c)connect instruments on the LT side
d)reduce the incidence of overvoltage surges on the transmission
Answer: improve the power factor of the transmission

83.What is the percentage increase of bus bar voltage required to compensate for the reactance drop, when the feeder having a reactance of 5% carries a full load current at a pf. 0.8 lagging?
a)5% b)1.2%
c)1.8% d)3%

84.A transformer is rated at 11 kV/0.4 kV 500kVa,5% reactance. What is the short circuit MVA of the transformer when connected to an infinite bus?
a)20 MVA b)10 MVA
c)15 MVA d)5 MVA

### Video Tutorial About Differential relay:

85.Resistance switching in normally employed in
a) all breakers
b) bulk oil barkers
c)minimum oil barkers
d)air blast circuit breakers

86.Reactance relay is normally preferred for production against
a) earth faults b) phase faults
c)open-circuit faults d) none of these

87.The use of high-speed circuit-breakers
a) reduces the short circuit current
b) improves system stability
c)decreases system stability
d)increases the short circuit current

88.In the protection of transformers, harmonic restraint is used to guard against
a) magnetizing inrush current
b) unbalanced operation
c)lightning
d)switching overvoltages

89.The unit protection scheme provides
a) primary protection
b) back up protection
c)simultaneous protection
d)remote protection

90. In a 400 kV power network, 360 kV is recorded at 400 kV bus. The reactive power absorbed by a shunt reactor for 50 Mar, 400 kV connected at the bus is
a)61.73 MVAr b)55.56MVAr
c)45.0 MVAr d)40.5 MVAr

Learn More:   7 Purpose of NGR Neutral Grounding Resistor Transformer & Generator

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Electrical Machines Objective Type Questions Gate Preparation-2 Transformer

91.The operation of the relay which is most affected due to arc resistance is
a) mho relay
b) reactance relay
c)impedance relay
d)all are equally affected

92.A 100/5 A bar primary current transformer supplies an O/C relay set at 25% pick up and it has a burden of 5 VA. The secondary voltage is
a)1 volt b)1.25 volts
c)2.5 volts d)4 volts

93.The plug setting of a negative sequence relay is 0.2 A. The current transformer ratio is 5:1. The minimum value of line to line fault current for the operation of the relay is
a)1 A b)1/1.732 A
c)1.732 A d)0.2/1.732 A

94.Mho relay is normally used for the protection of
a) long transmission lines
b) medium length lines
c)short length lines
d)no length criterion

95.The impedance value of generator is 0.2 pp. on a base value of 11kV, 50 MVA. The impedance value for a base value of 22 kV, 150 MVA is
a)0.15 pu. b)0.2 pu.
c)0.3 pu. d)2.4 pu.

96.The ratio of reset to pick up current for an induction cup relay is approximately
a)0.99 b)1.0
c)0.75 d) none of these

97.A reactance relay is
a) voltage restrained directional relay
b) directional restrained over-current relay
c)voltage restrained over-current relay
d)none of these

98.For protection of parallel feeders from one end, the relays required are
a) non-directional relays at the source end and directional relays at the load end
b) non-directional relays at both the ends
c)directional relays at the source end and non-directional at the load end
d)directional relays at both the ends
Answer: non-directional relays at the source end and directional relays at the load end

99.For the same rupturing capacity, the actual current to be interrupted by an HRC fuse is
a) much less than any circuit breaker
b) much more than any circuit breaker
c)equal to the circuit breaker
d)none of these
Answer: much less than any circuit breaker

100.To limit current chopping in vacuum circuit breakers, the contact material used has
a) high vapour pressure and low conductivity properties
b) high vapour pressure and high conductivity properties
c)low vapour pressure and high conductivity properties
d)low vapour pressure and low conductivity properties
Answer: low vapour pressure and low conductivity properties