Basic Concepts of HVDC — MCQs – EE

1. HVDC stands for:
(A) High Voltage Direct Current
(B) High Voltage Distribution Circuit
(C) Hybrid Voltage Direct Control
(D) High Voltage Double Conversion

2. The main purpose of HVDC is to:
(A) Transmit bulk power over long distances efficiently
(B) Reduce load power factor only
(C) Increase system frequency
(D) Supply low-voltage residential loads

3. The typical applications of HVDC include:
(A) Long-distance transmission and interconnection of asynchronous AC grids
(B) Short-distance residential distribution
(C) Low-voltage industrial power
(D) Harmonic filtering only

4. HVDC transmission uses:
(A) Direct current (DC) instead of alternating current (AC)
(B) Only AC current
(C) Only low-frequency AC
(D) Only single-phase AC

5. A converter station in HVDC systems is used to:
(A) Convert AC to DC and DC to AC
(B) Increase AC voltage only
(C) Store energy
(D) Correct power factor only

6. HVDC systems are classified into:
(A) Monopolar and bipolar systems
(B) Single-phase and three-phase AC only
(C) Step-up and step-down AC systems
(D) Reactive and active systems

7. In a monopolar HVDC system, the return path is usually:
(A) Through earth or metallic return
(B) Through a second conductor only
(C) Not required
(D) Through AC line only

8. Bipolar HVDC has:
(A) Two conductors with equal and opposite voltages
(B) One conductor with earth return
(C) Three-phase AC only
(D) Single conductor with no return

9. Line-commutated converters (LCC) use:
(A) Thyristors for rectification and inversion
(B) IGBTs only
(C) Diodes only
(D) SCRs for AC only

10. Voltage-source converters (VSC) use:
(A) IGBTs for fast switching and independent control
(B) Thyristors only
(C) Diodes only
(D) SCRs for AC only

11. HVDC is economical compared to HVAC for:
(A) Long-distance transmission and submarine cables
(B) Short-distance lines below 50 km
(C) Residential distribution only
(D) Low-voltage distribution only

12. Smoothing reactors in HVDC lines are used to:
(A) Reduce DC current ripple
(B) Correct voltage sag
(C) Store energy
(D) Improve AC frequency

13. Filters in HVDC systems are used to:
(A) Eliminate AC-side harmonics generated by converters
(B) Store energy
(C) Correct DC voltage only
(D) Increase AC voltage only

14. HVDC is preferred for undersea cables because:
(A) AC charging current is eliminated
(B) AC voltage is lower
(C) AC frequency can’t be controlled
(D) DC current is safer

15. HVDC monopolar system typically has:
(A) One main conductor and earth or metallic return
(B) Two conductors only
(C) Three-phase AC system
(D) Two AC lines and one DC line

16. HVDC bipolar system typically provides:
(A) Higher reliability and reduced earth current
(B) Lower DC voltage
(C) Higher AC losses
(D) Poor controllability

17. HVDC converters are connected to AC systems using:
(A) Transformers
(B) Capacitors only
(C) Inductors only
(D) Direct AC line only

18. HVDC control allows:
(A) Fast regulation of active and reactive power
(B) Only AC voltage control
(C) Frequency stabilization only
(D) Harmonic mitigation only

19. HVDC faults are more critical than AC faults because:
(A) DC current does not naturally pass through zero
(B) Voltage is lower
(C) Frequency changes rapidly
(D) Harmonics are eliminated

20. HVDC lines are usually:
(A) Overhead or underground/submarine
(B) Only overhead
(C) Only submarine
(D) Single-phase AC lines

21. HVDC is useful for interconnecting asynchronous AC grids because:
(A) Frequency differences between grids are tolerated
(B) Only voltage is regulated
(C) AC losses are reduced
(D) Load power factor is corrected

22. Advantages of HVDC transmission include:
(A) Lower losses, controllable power flow, and asynchronous interconnection
(B) Cheaper initial cost always
(C) Simple control
(D) Easy short-distance distribution

23. Disadvantages of HVDC transmission include:
(A) High converter cost and complex control
(B) High losses in long lines
(C) Poor reliability
(D) Short-distance lines are inefficient only

24. HVDC line reactors are used to:
(A) Limit fault currents and reduce ripple
(B) Correct voltage sags
(C) Store energy
(D) Improve AC frequency

25. HVDC multi-terminal systems connect:
(A) More than two converter stations in a common DC network
(B) Only two stations
(C) Only monopolar lines
(D) Only AC systems

26. Commutation failure in LCC-HVDC occurs due to:
(A) Weak AC voltage at the rectifier
(B) Strong DC voltage
(C) High transformer impedance
(D) Load imbalance only

27. VSC-HVDC systems can support:
(A) Black start of AC networks
(B) Only DC voltage
(C) Only AC voltage
(D) Only reactive power

28. Harmonics in HVDC systems are generated primarily by:
(A) Converters
(B) Transmission lines
(C) Transformers only
(D) Capacitors only

29. HVDC submarine cables are preferred over AC because:
(A) Capacitive charging current in AC is avoided
(B) DC voltage is lower
(C) AC frequency can’t be controlled
(D) AC losses are eliminated only for short distances

30. The main goal of HVDC transmission is to:
(A) Efficiently transmit large amounts of power over long distances and interconnect asynchronous AC grids
(B) Reduce reactive power only
(C) Supply residential loads only
(D) Correct frequency only