HVDCT MCQ COLLECTION

The HVDC converter

Does not consume reactive power

Consumes as much reactive power as real power

Consumes 50% of the real power

Ans. C

A back to back HVDC link can be advantageous compared to AC primarily because

It is cheaper

Of stability considerations

Of controlled power glow

Ans. C

A 12-pulse bridge is preferred in HVDC because

It eliminates certain harmonics

It results in better power factor

Series connection of converters on D.C. side is better

Ans. A

Fault on a two terminal DC link is removed by

Breakers on DC side

Breakers on AC side

Current control of converters

Ans. C

TRANSMISSION LINE

1. The surge impedance of a 110 kV, 3-phase transmission line is 440 ohms. The surge impedance
loading of the line is

a. 3 (110) 2/440 MW

b. (110) 2/440 MW

c. (110) 2/ 3110) 2 MW
Ans.: (b)

2.The capacitance and inductance per unit length of a 3-phase line, operating at 110 kV are .01
microfarad and 2.5 mH. The surge impedance of the line is

(a) 50 ohms

(b) 500 ohms

© 250 ohms

Ans: (b)

3. A long transmission line is energized at then sending end and is kept open circuited at the receiving
end. The magnitudes of the sending end voltage Vs and of the receiving end voltage Vr satisfy the
following relationship

a. Vs =Vr

b. Vs is greater than Vr

c. Vs is less than Vr

Ans: ©

4. Voltage regulation of a short transmission line is

a. always positive

b. always negative

c. either positive, negative, or zero

Ans: ©

5. The capacitance of an overhead line increases with

i. increase in mutual geometric mean distance

ii. increase in height of conductors above ground

a. Both are true

b. Both are false

c. Only (i) is correct

Ans: (b)
6. Shunt compensation for long EHV lines is primarily resorted to

a. improve voltage profile

b. improve stability

c. reduce fault currents

Ans: (a)

7. Series compensation is primarily resorted to

d. improve voltage profile

e. improve stability

f. reduce fault currents

Ans: (b)

8. Fair weather corona loss may be computed using the empirical formula given by Peterson. According
to Peterson’s formula corona loss is proportional to

(a) f and V2

(b) f 2 and V

a. f and V

where f and V are the system frequency and voltage respectively.

Ans: (a)

9. Bundled conductors are used in EHV lines primarily for

a. reducing cost of the line

b. reducing corona loss and radio interference

c. increasing stability limit.

Ans: (b)

10. There are 20 discs in the string of insulators of a 3-phase 400 kV transmission line. String efficiency is
80 %. The maximum voltage across any disc is
a. 25 kV

b. 25/ 3 kV

c. 25 3 kV

Ans: (b)

11. Two or three sheds or petticoats are provided in pin-type insulators in order to increase

a. creepage resistance

b. spark-over voltage(S.O.V)

c. puncture voltage

Ans: (a)

12. Pin -type insulators are use up to

a. 11 kV

b. 33kV

c. 132kV

Ans: (b)

13. Insulators used for transmission line at the dead -end tower are

a. suspension type

b. shackle type

c. strain type

Ans: ©

14. Economic studies have shown that D.C. transmission is cheaper than a. c transmission for lengths

a. a. below 300 km

b. b. beyond 600 km

c. c. beyond 1200 km

Ans. B
15.Transmission voltages in the range 230 kV-765 kV are known as

a. a. High voltage

b. b. Extra High Voltage

c. c. Ultra High Voltage

Ans. B

16. Which one of the following statements is false?

As the transmission voltage increases,

a. a. Corona loss decreases

b. b. Conductor copper loss decreases

c. c. Cost of insulators, transformers, switches & circuit breakers increases

Ans. C

17. The internal inductance of a solid conductor of radius r and carrying a current I is equal to

a. a. 0.5 I * 10-7 H/m

b. b. 0.5 I * 10-7 exp(-1/4)*r H/m

c. c. 0.5 * 10-7 H/m

Ans. C

18. Which one of the following statements is not true?

a. a. The GMD method of finding inductance does not apply to ACSR conductors

b. b. Current density in ACSR conductors is uniform

c. c. The GMD between two circular areas, each of different diameters, is equal to the distance
between their centres.

Ans. B

19. Expanded ACSR conductors are used

a. a. To increase the tensile strength of the line

c. c. To reduce I2R loss

Ans. B

20. A conductor with 19 strands, each of same diameter and each having an inductance of L Henries
is used for a transmission line. The total inductance of the conductor will be

a. a. L/19

b. b. L/361

c. c. 19L

Ans. A

21. The line to neutral capacitance of single -phase line with conductors of radius 1cm and spaced
1m apart is equal to

a. a. 10-9/72 F/m

b. b. 10-9/36pF/m

c. c. 2 p210-7 F/m

Ans .a

22. In a double-circuit line with hexagonal spacing ,

a. a. The phases are balanced, but the conductors of each individual phase are not balanced.

b. b. The conductors of each individual phase are balanced , but the phases are not balanced

c. c. The phases, and the conductors of each individual phase are both balanced

Ans. C

23. Which one of the following statements is true?

b. Skin effect at 50 Hz is negligible whatever the diameter of the conductor.

c. Skin effect at 50 Hz is negligible for the smaller diameter conductors but becomes appreciable for
the larger conductor conductor.

Ans. C

24. Which one of the following statements is true?

a. Resistance of a conductor decreases and the internal inductance increases as the frequency is
increased

b. Resistance and internal inductance of a conductor both increase with increase of frequency

c. Resistance of a conductor increases and the internal inductance decreases as the frequency is
increased

Ans. C

25. The surge impedance of a double-circuit power transmission line is

a. 40 ohms

b. 200 ohms

c. 400 ohms

d. 800 ohms

Ans. B

26. The surge impedance of a telephone line is

a. 50 ohms
b. 75 ohms

c. 200 ohms

d. 400 ohms

Ans. B

27. Bundle conductors are preferred in EHV transmission lines because

a. It is easy to fabricate thin conductors and combine them to make a bundle

b. Inductance of the line is reduced, and the corona loss, and radio & TV interference is minimized.

c. Tower height is reduced and hence transmission cost is low.

Ans. B

28. Inductive interference between power & communication lines can be minimized by

a. a. Increasing the spacing of power line conductors

b. b. Transposing power line conductors

c. c. Transposing communication line conductors

d. d. Either b or c.

Ans. D

29. The percentage regulation of an overhead transmission line can be zero when the load power
factor is

a. a. Lagging

b. b. Unity

c. c. Leading
Ans. C

18. 29. Which one of the following statements is true?

a. a. Skin effect increases the resistance of a conductor ,but proximity effect decreases the
resistance

b. b. Both skin effect and proximity effect increase the resistance of a conductor

c. c. Both skin effect and proximity effect increase the internal inductance of a conductor

Ans. B

19. 30. A transmission line having parameters A1, B1, C1, D1 is in parallel with another having
parameters A2, B2, C2, D2. The overall “ A “ parameter of the combination is

a. a. A1A2 +B1C2

b. b. (A1B2 +A2B1)/(B1+B2)

c. c. C1+C2 + (A1-A2)(D2-D1)/(B1+B2)

Ans. B

18. 31. Disruptive critical voltage is

a. a. Equal to

b. b. Greater than

c. c. Less than

visual critical voltage for corona on an overhead line.

19. 32. Corona loss

a. a. Increases

b. b. Decreases

c. c. Does not change

the switching voltage on a transmission line.

Ans. B

20. 33. Handling of the telephone receiver may become dangerous due to

a. a. Electromagnetic induction

b. b. Electrostatic induction

c. c. Both electromagnetic and electrostatic induction

from a power line.

Ans. B

21. 34. Mutual inductance between a three -phase power line and a telephone line due to third
harmonic current in the power line is

a. a. The algebraic sum of mutual inductances from individual phase wires

b. b. The arithmetic sum of mutual inductances from individual phase wires

c. c. Zero

Ans. B

22. 35. Dielectric strength of mechanically sound porcelain is

b. b. 22 kV/cm

c. c. 65 kV/cm

d. d. 100 kV/cm

Ans. C

23. 36. Dielectric strength of glass is

a. a. 22 kV/cm

b. b. 60-66 kV/cm

c. c. 140 kV/cm

d. d. 240 kV/cm

Ans. C

24. 37. Which one of the following statements is true?

a. a. For 11 kV insulators, the ratio of wet spark-over voltage to working voltage is 8.3

b. b. For 66 kV insulators, the ratio of dry spark-over voltage to working voltage is 8.3

c. c. For 11 kV insulators, the ratio of dry spark-over voltage to working voltage is 8.3

Ans. C

25. 38. Which one of the following statements is true?

a. a. Flash-over tests are performed on all insulators

c. c. Design tests are done on ½ percent of insulators supplied

Ans. None of the above

26. 39. Which one of the following statements is true?

a. a. The spark-over voltage is less than the puncture voltage

b. b. The spark-over voltage is greater than the puncture voltage

c. c. The spark-over voltage is equal to the puncture voltage

Ans. A

27. 40. Which one of the following statements is true?

The sheds of an insulator should be shaped

a. a. To conform to the electrostatic tube of force and the body should be shaped to conform to
the equipotential surfaces

b. b. To conform to the equipotential surfaces and the body should be shaped to conform to the
electrostatic tubes of force

c. c. To conform to the equipotential surfaces and so also the body

Ans. B

28. 41. In a suspension insulator, the mechanical stresses on the conductor are

a. a. Increased

b. b. Reduced

c. c. The same
Ans. B

29. 42. The string efficiency of the insulator can be increased by

a. a. Increasing the number of strings in the insulator

b. b. Increasing the ratio , capacitance to earth/capacitance per insulator

c. c. By the correct grading of various capacitances

d. d. Decreasing the number of strings

Ans. C

30. 43. String efficiency of insulators for wet flash-over is

a. a. Less

b. b. More

c. c. The same

as that for dry flash-over

Ans. B

31. 44. The potential across insulator discs can be equalized by having

a. a. The same capacitance for each unit

b. b. The highest capacitance for the lowest unit and decreasing progressively the capacitance of
other units

c. c. The lowest capacitance for the lowest unit and increasing progressively the capacitance of
other units

Ans. B
32. 45. Grading ring serves the purpose of

a. a. Equalizing the voltage distribution across discs

b. b. An arcing shield

c. c. Both equalizing the voltage distribution and acting as an arcing shield

Ans. C

Taken from http://onlinemcqtest.blogspot.com/