11. The concept of electrically short, medium and long line is primarily based on the
a) nominal voltage of the line
b) physical length of the line
c) wavelength of the line
d) power transmitted over the line
ans. b
12. For a fixed value of complex power flow in a transmission line having a sending end voltage V, the real power loss will be proportional to
a) V
b) V square
c) 1/V square
d) 1/V
ans. b
13. A transmission line has equal voltages at the two ends , maintained constant by two sources. A third source is to be provided to maintain constant voltage (equal to end voltages) at either the mid point of the line or at 755 of the distance from the sending end. Then the maximum power transfer capabilities of the line in the original case and the other two cases respectively will be in the following ratios
a) 1:1:1
b) 1:2:1/0.75
c) 1:2:4
d) 1:4:16
ans. a
14. A single phase transmission line and a telephone line are both symmetrically strung one below the other , in horizontal configurations , on a common tower. The shortest and longest distances between the phase and the telephone conductors are 2.5 m and 3 m respectively. The voltage(volt/km) induced in the telephone circuit , due to 50 Hz current of 100 amps in the power circuit is
a) 4.81
b) 3.56
c) 2.29
d) 1.27
ans. d
15. A long wire composed of a smooth round conductor runs above and parallel to the ground( assumed to be large conducting plane) . A high voltage exists between the conductor and the ground. The maximum electric stress occurs at
a) the upper surface of the conductor
b) the lower surface of the conductor
c) the ground surface
d) midway between the conductor and ground
ans. b
16. The total reactance and total susceptance of a lossless overhead EHV line, operating at 50Hz , are given by 0.045 and 1.2 pu respectively. If the velocity of wave propagation is 3x10^5 km/s, then the approximate length of the line is
a) 122 km
b) 172 km
c) 222 km
d) 272 km
ans. b
17. 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. The the percentage ratio of line length to wavelength will be given by
a) 24.24 %
b) 12.12 %
c) 19.05 %
d) 6.06 %
ans. d
18. A surge of 20 kV magnitude travels along a lossless cable towards its junction with two identical lossless overhead transmission lines. The inductance and the capacitance of the cable are 0.4 mH and 0.5 microF per km. The inductance and capacitance of the overhead transmission lines are 1.5 mH and 0.015 microF per km. The magnitude of the voltage at the junction due to surge is
a) 36.72 kV
b) 18.36 kV
c) 6.07 kV
d) 33.93 kV
ans. a
19. Serier capacitive compensation in EHV transmission lines is used to
a) reduce the line loading
b) improve the stability of the system
c) reduce the voltage profile
d) improve the protection of the line
ans. b
20. At an industrial substation with a 4 MW load, a capacitor of 2 MVAR is installed to maintain the load power factor at 0.97 lagging. If the capacitor goes out of service , the load power factor becomes
a) 0.85
b) 1.00
c) 0.80 lag
d) 0.90 lag
ans. c
a) nominal voltage of the line
b) physical length of the line
c) wavelength of the line
d) power transmitted over the line
ans. b
12. For a fixed value of complex power flow in a transmission line having a sending end voltage V, the real power loss will be proportional to
a) V
b) V square
c) 1/V square
d) 1/V
ans. b
13. A transmission line has equal voltages at the two ends , maintained constant by two sources. A third source is to be provided to maintain constant voltage (equal to end voltages) at either the mid point of the line or at 755 of the distance from the sending end. Then the maximum power transfer capabilities of the line in the original case and the other two cases respectively will be in the following ratios
a) 1:1:1
b) 1:2:1/0.75
c) 1:2:4
d) 1:4:16
ans. a
14. A single phase transmission line and a telephone line are both symmetrically strung one below the other , in horizontal configurations , on a common tower. The shortest and longest distances between the phase and the telephone conductors are 2.5 m and 3 m respectively. The voltage(volt/km) induced in the telephone circuit , due to 50 Hz current of 100 amps in the power circuit is
a) 4.81
b) 3.56
c) 2.29
d) 1.27
ans. d
15. A long wire composed of a smooth round conductor runs above and parallel to the ground( assumed to be large conducting plane) . A high voltage exists between the conductor and the ground. The maximum electric stress occurs at
a) the upper surface of the conductor
b) the lower surface of the conductor
c) the ground surface
d) midway between the conductor and ground
ans. b
16. The total reactance and total susceptance of a lossless overhead EHV line, operating at 50Hz , are given by 0.045 and 1.2 pu respectively. If the velocity of wave propagation is 3x10^5 km/s, then the approximate length of the line is
a) 122 km
b) 172 km
c) 222 km
d) 272 km
ans. b
17. 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. The the percentage ratio of line length to wavelength will be given by
a) 24.24 %
b) 12.12 %
c) 19.05 %
d) 6.06 %
ans. d
18. A surge of 20 kV magnitude travels along a lossless cable towards its junction with two identical lossless overhead transmission lines. The inductance and the capacitance of the cable are 0.4 mH and 0.5 microF per km. The inductance and capacitance of the overhead transmission lines are 1.5 mH and 0.015 microF per km. The magnitude of the voltage at the junction due to surge is
a) 36.72 kV
b) 18.36 kV
c) 6.07 kV
d) 33.93 kV
ans. a
19. Serier capacitive compensation in EHV transmission lines is used to
a) reduce the line loading
b) improve the stability of the system
c) reduce the voltage profile
d) improve the protection of the line
ans. b
20. At an industrial substation with a 4 MW load, a capacitor of 2 MVAR is installed to maintain the load power factor at 0.97 lagging. If the capacitor goes out of service , the load power factor becomes
a) 0.85
b) 1.00
c) 0.80 lag
d) 0.90 lag
ans. c
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