HVDC Transmission — MCQs – EE

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

2. The main advantage of HVDC over HVAC for long distances is:
(A) Lower transmission losses
(B) Lower initial cost always
(C) Simpler insulation
(D) No need for converters

3. HVDC is preferred for:
(A) Long-distance bulk power transmission and interconnecting asynchronous grids
(B) Short-distance residential distribution
(C) Low-voltage industrial supply
(D) Only for reactive power compensation

4. The converter in HVDC systems is used to:
(A) Convert AC to DC (rectifier) and DC to AC (inverter)
(B) Increase AC voltage
(C) Store energy
(D) Filter harmonics only

5. Line-commutated converters (LCC) in HVDC use:
(A) Thyristors
(B) IGBTs
(C) Diodes only
(D) SCRs for AC only

6. Voltage-source converters (VSC) in HVDC use:
(A) IGBTs
(B) Thyristors
(C) Diodes only
(D) SCRs for AC only

7. The main disadvantage of LCC-HVDC is:
(A) Requirement of strong AC system for commutation
(B) High cost for long distances
(C) Low efficiency
(D) Poor voltage regulation

8. VSC-HVDC allows:
(A) Independent control of active and reactive power
(B) Only active power transfer
(C) Only DC current control
(D) No reactive power support

9. The typical DC voltage level for HVDC transmission is:
(A) ±200 kV to ±800 kV
(B) 11 kV to 33 kV
(C) 132 kV to 220 kV
(D) 50 kV only

10. The main components of an HVDC system are:
(A) Converters, DC transmission line, filters, and smoothing reactors
(B) Transformers only
(C) Capacitor banks only
(D) Generators only

11. Smoothing reactors in HVDC lines are used to:
(A) Reduce DC current ripple
(B) Increase AC voltage
(C) Reduce reactive power
(D) Improve harmonics only

12. Filters in HVDC systems are used to:
(A) Suppress AC side harmonics
(B) Store energy
(C) Control DC voltage
(D) Increase line voltage

13. HVDC is particularly advantageous for undersea cables because:
(A) Capacitive charging current in AC cables is eliminated
(B) It reduces active power
(C) It increases reactive power
(D) AC voltage can’t be applied

14. Monopolar HVDC has:
(A) Single conductor with return path through earth or metallic return
(B) Two conductors with equal voltage
(C) Three-phase AC system
(D) No DC voltage

15. Bipolar HVDC has:
(A) Two conductors with opposite polarity
(B) One conductor with earth return only
(C) Three-phase AC line
(D) Single conductor with no return

16. Advantages of HVDC include:
(A) Lower losses, asynchronous interconnection, and better controllability
(B) Lower cost always
(C) No need for converters
(D) Simpler design for short lines

17. Disadvantages of HVDC include:
(A) High initial cost of converters and complex control
(B) High losses in long lines
(C) Voltage regulation issues only
(D) Poor reliability

18. DC line reactors are used to:
(A) Limit fault currents in HVDC systems
(B) Correct power factor
(C) Improve AC voltage only
(D) Reduce frequency deviation

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

20. HVDC control systems allow:
(A) Fast control of active and reactive power, and system stability improvement
(B) Only frequency control
(C) Only voltage regulation
(D) Only harmonic filtering

21. Multi-terminal HVDC systems are:
(A) Systems with more than two converter stations connected to a common DC network
(B) Two-terminal HVDC systems only
(C) Only monopolar systems
(D) Only for AC distribution

22. HVDC faults are more critical than AC faults because:
(A) DC current doesn’t naturally pass through zero
(B) Voltage is lower
(C) Frequency changes rapidly
(D) Harmonics are zero

23. Earth return is used in HVDC monopolar systems to:
(A) Reduce the number of conductors required
(B) Increase DC voltage
(C) Reduce AC voltage
(D) Improve harmonic performance only

24. HVDC transmission is more economical than HVAC for:
(A) Distances greater than 500–600 km for overhead lines and 50 km for submarine cables
(B) Short distances below 50 km
(C) Only low-voltage lines
(D) Only residential distribution

25. Converters in HVDC systems are typically connected to AC lines via:
(A) Transformers
(B) Capacitors only
(C) Reactors only
(D) Direct lines with no isolation

26. Commutation failure in HVDC LCC systems occurs due to:
(A) Weak AC voltage at the rectifier
(B) Strong DC current only
(C) Excessive line capacitance only
(D) No AC voltage at inverter

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

28. HVDC for asynchronous interconnection allows:
(A) Power exchange between grids with different frequencies
(B) Only synchronous grids
(C) AC frequency stabilization only
(D) Reactive power exchange only

29. Advantages of bipolar HVDC over monopolar include:
(A) Higher reliability, reduced earth current, and balanced voltage
(B) Lower initial cost only
(C) No converter needed
(D) Shorter line distance only

30. The main purpose of HVDC transmission is to:
(A) Efficiently transmit large amounts of power over long distances and interconnect asynchronous networks
(B) Supply residential loads only
(C) Replace transformers only
(D) Correct power factor only