EE8017 - HVDC - Unit 4

ChettinadTech Dept of EEE
Department of Electrical and Electronics Engineering

EE8017- High Voltage Direct Current Transmission
Unit IV - MCQ Bank
1. Match the following:
Controllers Functions
1) AC Controller i) AC to DC
2) Rectifier ii) Fixed Amplitude of AC into Variable Amplitude of AC
3) Inverter iii) DC to AC
Option:
a) 1)-ii), 2)-i), 3)-iii)
b) 1)-i), 2)-ii), 3)-iii)
c) 1)-iii), 2)-ii), 3)-i)
Answer: a) 1)-ii), 2)-i), 3)-iii)
2. ______________ is an AC controller which varies the applied voltage applied to the Inductor
a) TCSC
b) TCPST
c) TCR
d) STATCOM
Answer: c) TCR
3. Which Controller output voltage will be in quadrature with line current Independently
a) SSSC
b) TCSC
c) SVC
d) STATCOM
Answer: a) SSSC
EE8017- High Voltage Direct Current Transmission Page 1

4. Power transfer through AC systems depends on

a) sending and receiving end voltages
b) phase angle difference between sending end and receiving end voltages
c) reactance of the line
d) all of the above
Answer: d) All of the above
5. Power transfer in DC line depends on

a) sending and receiving end voltages
b) number of pulses in the rectifier
c) line resistance
d) none of the above
Answer: a) sending and receiving end voltages
6. Advantage of DC link for power transfer is

a) easy controllability of power
b) more economical
c) it is an asynchronous tie
d) less insulation requirement
Answer: a) easy controllability of power
7. Control of power in DC link is necessary because

a) current order setting needs to be done
b) power can be reversed
c) current sensitive to voltage changes and may damage the converters
d) all of the above
Answer: c) current sensitive to voltage changes and may damage the converters
8. With increase in delay angle α

a) p.f. is reduced
b) DC voltage decreases
c) both (a) and (b)

d) kVAR requirement decreases
Answer: c) both (a) and (b)
9. For inversion or inverter operation

a) α ≤ 90°
b) α > 90°
c) 90° < α < 180°
d) 180° < α < 270°
Answer: c) 90° < a < 180°
10. For stable operation of DC systems

a) CC and CEA control is adopted
b) α control, CC and CEA is adopted
c) only CEA control is adopted
d) only CC control is adopted
Answer: b) α control, CC and CEA is adopted
11. Extinction angle У is optimised so that

a) DC current is kept minimum
b) kVAR requirement is minimum
c) DC output voltage is minimum
d) all of the above
Answer: b) kVAR requirement is minimum
12. Characteristic of a converter is the relation between

a) AC voltage and Id
b) DC output voltage and Id
c) DC power and Id
d) α and Id
Answer: b) DC output voltage and Id
13. The common control done in converters is

a) rectifier as both voltage and current controller
b) inverter as both voltage and current controller
c) inverter as current controller
d) rectifier as voltage controller and inverter as current controller
Answer: d) rectifier as voltage controller and inverter as current controller
14. Power reversal in DC link is done

a) operating rectifier (α) close to 180° and inverter (У) close to zero
b) operating both (α) and (У) near 90°
c) operating α at 90° and У close to zero
d) operating У close to 90° and α near zero
Answer: a) operating rectifier (α) close to 180° and inverter (У) close to zero
15. In case of IPC cosine control, DC output voltage is proportional to

a) control voltage
b) DC current
c) cos–1 of phase angle on AC side
d) overlap angle µ
Answer: a) control voltage
16. Main drawback of CEA control is

a) it cannot offer stable operation in weak AC links
b) more reactive kVAR are needed
c) control is uneconomical
d) generates harmonics
Answer: a) it cannot offer stable operation in weak AC links
17. Firing angle control in modern HV converters is

a) IFC
b) EPC
c) IPC
d) both (a) and (b)
Answer: d) both (a) and (b)
18. In HVDC link with CC control

a) power loss is more
b) short circuit current is limited
c) both (a) and (b)
d) none of the above
Answer: c) both (a) and (b)
19. Commutation failure usually occurs in

a) rectifiers
b) inverters
c) both inverters and rectifiers
d) controllers
Answer: a) rectifiers
20. In order bring the voltage of operation to the normal voltage level as the power varies,
control done is
a) α control
b) transformer tap changing
c) У control
d) both α and У control
Answer: b) transformer tap changing
21. technology is often used as a synchronous voltage source

a) Current Source Converter
b) Voltage Source Converter
c) Both a) and b)
d) None
Answer: b) Voltage Source Converter
22. Which of the following are power flow control method?

a) Fundamental frequency control
b) Pulse width modulation
c) Both a) and b)
Answer: c) Both a) and b)
23. If capacitor is interfaced with the ac supply through an ac controller, then a _________ must be
added to limit the inrush current
a) Series Capacitor
b) Series Inductor
c) Shunt capacitor
d) Shunt Inductor
Answer: b) series Inductor
24. ______________ is an ac controller which varies the voltage applied to the inductor.
a) TCSC
b) TCR
c) TCPST
Answer: b) TCR
25. ________________ is an ac controller which provides continuously controllable lagging VARs and
line voltage dependent.
a) TCSC
b) TCR
c) TCPST
Answer: b) TCR

26. ________________ is an ac controller to continue adjust the apparent reactance inserted in series
with the line
a) TCSC
b) TCR
c) TCPST
Answer: a) TCSC
27. ______________ is an ac controller which allows the control of the load angle between two buses
in a transmission line
a) TCSC
b) TCR
c) TCPST
Answer: c) TCPST
28. ______________ is varied by injection in series of a controlled amount of voltage in quadrature

with the line phase shift
a) Current Phase Shift
b) Voltage Phase Shift
Answer: b) Voltage Phase Shift
29. The use of ______________ switching device allows gating the switches more than one cycle
a) Force Commuted
b) Self-Commutated
Answer: b) Self-Commutated
30) The DC side harmonics increases significantly as delay angle move towards _____________
a) 300
b) 600
c) 900
d) 1200
Answer: c) 900
31) Thyristor rectifier act as an ____________ load

a) Inductive
b) Capacitor
Answer: a) Inductive
32) In the case of Thyristor Rectifier the power factor is ____________ for all operating conditions
a) Lagging
b) Leading
c) Unity
Answer: a) Lagging
33) For a delay angle of _________ the converter operates as a reactive power compensator
a) 300
b) 600
c) 900
d) 1200
Answer: c) 900
34) Lagging reactive power limitation is removed when thyristor replace by __________
a) Force Commuted Device
b) Self-Commutated Device
Answer: b) Self-Commutated Device
35) device allows implementation of PWM Pattern

a) Capacitive Reactive Compensator
b) Self-Commutated Device
c) Both a) and b)
Answer: c) Both a) and b)

35) In the PWM method

a) external commutating capacitors are required
b) more average output voltage can be obtained
c) lower order harmonics are minimized
d) higher order harmonics are minimized
Answer: c)
36) Which of the following is not a PWM technique?

a) Single-pulse width modulation
b) Multiple-pulse width modulation
c) Triangular-pulse width modulation
d) Sinusoidal-pulse width modulation
Answer: c)
37) In pulse width modulation

a) the output voltage is modulated
b) the input voltage is modulated
c) the gating pulses are modulated
d) none of the mentioned
Answer: c)
38) What are the effects of trouble caused by harmonics?

A. Harmonics
B. Voltage collapse
C. Over heating
D. Decrease magnetic loss
Answer: C. Over heating
39. The index THD can be calculated for

A. Current
B. Voltage
C. Current and voltage

D. Current or voltage
Answer: D. Current or voltage
40. What are the means to reduce harmonics?

A. Using filter and increasing the pulse number
B. Decreasing the pulse number
C. Using filter only
D. None of the above
Answer: A. Using filter and increasing the pulse number
41. What are the sources of harmonics?

A. Arcing devices and electronics and medical test equipment
B. Phase controllers and AC regulators
C. All of the above
Answer: A. Arcing devices and electronics and medical test equipment
42. What is the use of tap changing transformer in HVDC systems?

A. Increase power factor obtained in ac side
B. Decrease power factor obtained in dc side
C. Increase power factor obtained in dc side
D. Decrease power factor obtained in ac side
Answer: A. Increase power factor obtained in ac side
43. The harmonics contained in the current waveform is given by

a. (np+1)
b. (np-1)
c. (np±1)
d. None of the above
Answer: C. (np±1)
44. Which of the following is not the feature of converter control?

a. Current order setting can be quickly and reliably changed depending on the requirement
b. Power reversal can be done easily and quickly
c. The stability margin is moderate
Answer: C. The stability margin is moderate
45. Smoothing reactor is used on DC side to ______________ DC current

a. Increase
b. Decrease
c. Smooth
Answer: C. Smooth
46. When the three phase system is not grounded and if single line to ground fault occurs, the
voltage of the other two healthy phases will
a. Increases
b. Decreases
c. Remains unaffected
Answer: A. Increases
47. For an EHV equipment for maintenance first it should be isolated and connected to ground
because
a. To provide low impedance
b. To discharge the charging capacitance to ground
c. Protection for operating personnel
d. Both B and C
Answer: D. Both B and C

48. The major components of a HVDC transmission system are ____________

a. Converter transformer
b. Converter station
c. Smoothing reactor
d. Dc filter
Answer: B. Converter station
49. Smoothing reactor reduce the possibility of in inverter

a. Voltage
b. Current
c. Commutation failure
Answer: C. Commutation failure
50. The smoothing reactor is connected in _____________ with the converters

a. Series
b. Parallel
c. Both A and B
Answer: A. Series
51. ____________ decrease the harmonic voltages and currents in the DC line
A. Smoothing reactor
B. AC filter
C. DC filter
Answer: A. Smoothing reactor
52. The smoothing reactor is connected before

a. AC filter
b. DC filter
c. Reactor

Answer: B. DC filter
53. A 12 pulse converter is obtained by series connection of two bridges with

a. 60 deg phase displacement between two source voltages
b. 30 deg phase displacement between two source voltages
c. 120 deg phase displacement between two source voltages
d. 90 deg phase displacement between two source voltages
Correct Answer: B. 30 deg phase displacement between two source voltages

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ChettinadTech Dept of EEE

Department of Electrical and Electronics Engineering

EE8017- High Voltage Direct Current Transmission Page 1

4. Power transfer through AC systems depends on

5. Power transfer in DC line depends on

6. Advantage of DC link for power transfer is

7. Control of power in DC link is necessary because

8. With increase in delay angle α

c) both (a) and (b)

9. For inversion or inverter operation

10. For stable operation of DC systems

11. Extinction angle У is optimised so that

12. Characteristic of a converter is the relation between

13. The common control done in converters is

14. Power reversal in DC link is done

15. In case of IPC cosine control, DC output voltage is proportional to

16. Main drawback of CEA control is

17. Firing angle control in modern HV converters is

18. In HVDC link with CC control

19. Commutation failure usually occurs in

21. technology is often used as a synchronous voltage source

22. Which of the following are power flow control method?

EE8017- High Voltage Direct Current Transmission Page 6

28. ______________ is varied by injection in series of a controlled amount of voltage in quadrature

31) Thyristor rectifier act as an ____________ load

35) device allows implementation of PWM Pattern

EE8017- High Voltage Direct Current Transmission Page 8

35) In the PWM method

36) Which of the following is not a PWM technique?

37) In pulse width modulation

38) What are the effects of trouble caused by harmonics?

39. The index THD can be calculated for

C. Current and voltage

40. What are the means to reduce harmonics?

41. What are the sources of harmonics?

42. What is the use of tap changing transformer in HVDC systems?

43. The harmonics contained in the current waveform is given by

44. Which of the following is not the feature of converter control?

45. Smoothing reactor is used on DC side to ______________ DC current

EE8017- High Voltage Direct Current Transmission Page 11

48. The major components of a HVDC transmission system are ____________

49. Smoothing reactor reduce the possibility of in inverter

50. The smoothing reactor is connected in _____________ with the converters

52. The smoothing reactor is connected before

d. None of the above

53. A 12 pulse converter is obtained by series connection of two bridges with

EE8017- High Voltage Direct Current Transmission Page 13

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