11. In an inverse definite minimum time, electromagnetic type over-current relay , the minimum time feature is achieved because of
a) Saturation of the magnetic circuit
b) proper mechanical design.
c) appropriate time-delay element
d) electromagnetic damping.
ans.a
12. In a biased differential relay the bias is defined as a ratio of
a) number of turns of restraining and operating coil.
b) operating coil current and restraining coil current.
c) fault current and operating coil current.
d) fault current and restraining coil current.
ans. b
13. A 75 MVA , 10 kV synchronous generator has Xd=0.4 pu.The Xd value (in pu) to a base of 100 MVA ,11 kV is
a) 0.578
b) 0.279
c) 0.412
d) 0.44
and d
14. The plug setting of a negative sequence relay is 0.2 A. The current transformer ratio 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
ans. a
15. The neutral of 10 MVA , 11kV alternator is earthed through a resistance of 5 ohms. The earth fault relay is set to operate at 0.75 A. The CT's have a ratio of 1000/5. What percentage of the alternator winding is protected?
a) 85 %
b) 88.2 %
c) 15 %
d) 11.8 %
ans. b
16. For the protection f transformers, harmonic restraint is used to guard against
a) magnetizing inrush current
b) unbalanced operation
c) lighting
d) switching over voltage
ans. a
17. Voltage phasors at the two terminals of a transmission line of length 70 km have a magnitude of 1.0 per unit but are 180 degrees out of phase. Assuming that the maximum load current in the line is 1/5th of minimum 3-phase fault current. Which one of the following transmission line protection schemes will NOT pick up for this condition?
a) Distance protection using mho relays with zone-1 set 80% of the line impedance.
b) Directional over current protection set to pick up at 1.25 times the maximum load current.
c) Pilot relaying system with directional comparison scheme.
d) Pilot relaying system with segregated phase comparison.
ans. a
18. In a 3-step distance protection , the reach of the three zones of the relay at the beginning of the first line typically extends into
a) 100% of the first line, 50 % of the second line and 20% of the third line.
b) 80 %of the first line, 50 % of the second line and 20% of the third line.
c) 80% of the first line, 50 % of the second line and 10% of the third line.
d) 50% of the first line, 50 % of the second line and 20% of the third line.
ans. b
19. An extra high voltage transmission line of length 300 km can be approximated by a lossless line having propagation constant beta =0.00127 radians per km. Then the percentage ratio of line length to wavelenth will be given by
a) 24.24%
b) 12.12 %
c) 19.05 %
d) 6.06%
ans. d
20. An overheade line having a surge impedance of 400 ohm is connected in series with an underground cable having a surge impedance of 100 ohm. If a surge of 50 kV travels from the line end towards the line-cable junctions, the value of the transmitted voltage wave at the junction is
a) 30 kV
b) 20 kV
c) 80 kV
d) -30 kV
ans. b
a) Saturation of the magnetic circuit
b) proper mechanical design.
c) appropriate time-delay element
d) electromagnetic damping.
ans.a
12. In a biased differential relay the bias is defined as a ratio of
a) number of turns of restraining and operating coil.
b) operating coil current and restraining coil current.
c) fault current and operating coil current.
d) fault current and restraining coil current.
ans. b
13. A 75 MVA , 10 kV synchronous generator has Xd=0.4 pu.The Xd value (in pu) to a base of 100 MVA ,11 kV is
a) 0.578
b) 0.279
c) 0.412
d) 0.44
and d
14. The plug setting of a negative sequence relay is 0.2 A. The current transformer ratio 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
ans. a
15. The neutral of 10 MVA , 11kV alternator is earthed through a resistance of 5 ohms. The earth fault relay is set to operate at 0.75 A. The CT's have a ratio of 1000/5. What percentage of the alternator winding is protected?
a) 85 %
b) 88.2 %
c) 15 %
d) 11.8 %
ans. b
16. For the protection f transformers, harmonic restraint is used to guard against
a) magnetizing inrush current
b) unbalanced operation
c) lighting
d) switching over voltage
ans. a
17. Voltage phasors at the two terminals of a transmission line of length 70 km have a magnitude of 1.0 per unit but are 180 degrees out of phase. Assuming that the maximum load current in the line is 1/5th of minimum 3-phase fault current. Which one of the following transmission line protection schemes will NOT pick up for this condition?
a) Distance protection using mho relays with zone-1 set 80% of the line impedance.
b) Directional over current protection set to pick up at 1.25 times the maximum load current.
c) Pilot relaying system with directional comparison scheme.
d) Pilot relaying system with segregated phase comparison.
ans. a
18. In a 3-step distance protection , the reach of the three zones of the relay at the beginning of the first line typically extends into
a) 100% of the first line, 50 % of the second line and 20% of the third line.
b) 80 %of the first line, 50 % of the second line and 20% of the third line.
c) 80% of the first line, 50 % of the second line and 10% of the third line.
d) 50% of the first line, 50 % of the second line and 20% of the third line.
ans. b
19. An extra high voltage transmission line of length 300 km can be approximated by a lossless line having propagation constant beta =0.00127 radians per km. Then the percentage ratio of line length to wavelenth will be given by
a) 24.24%
b) 12.12 %
c) 19.05 %
d) 6.06%
ans. d
20. An overheade line having a surge impedance of 400 ohm is connected in series with an underground cable having a surge impedance of 100 ohm. If a surge of 50 kV travels from the line end towards the line-cable junctions, the value of the transmitted voltage wave at the junction is
a) 30 kV
b) 20 kV
c) 80 kV
d) -30 kV
ans. b
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