- The HVDC converter
- Does not consume reactive power
- Consumes as much reactive power as real power
- Consumes 50% of the real power
- A back to back HVDC link can be advantageous compared to AC primarily because
- It is cheaper
- Of stability considerations
- Of controlled power glow
- 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
- Fault on a two terminal DC link is removed by
- Breakers on DC side
- Breakers on AC side
- Current control of converters
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
(c) 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: (c)
4. Voltage
regulation of a short transmission line is
a.
always positive
b.
always negative
c.
either positive, negative, or
zero
Ans: (c)
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: (c)
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
b.
b.
To reduce corona loss
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?
a.
Skin effect at 50 Hz is
negligible for larger diameter conductors but becomes appreciable for smaller
conductor.
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