High Voltage Engineering MCQs

1. What is the breakdown voltage of air at sea level?
A) 10 kV/cm
B) 20 kV/cm
C) 30 kV/cm
D) 40 kV/cm
Answer: A) 10 kV/cm

2. Corona discharge occurs when:
A) Insulation material fails
B) Electric field strength exceeds a critical value
C) Voltage is too low to ionize air
D) Conductors are too far apart
Answer: B) Electric field strength exceeds a critical value

3. The purpose of grading rings in a high voltage cable is to:
A) Improve mechanical strength
B) Reduce corona loss
C) Reduce electrical stress at the conductor surface
D) Enhance insulation resistance
Answer: C) Reduce electrical stress at the conductor surface

4. Which material is commonly used as an insulating gas in high voltage applications?
A) Nitrogen
B) Oxygen
C) Sulfur hexafluoride (SF6)
D) Carbon dioxide
Answer: C) Sulfur hexafluoride (SF6)

5. The breakdown in a gas occurs when:
A) Electrons escape from atoms
B) Electric field is greater than the dielectric strength
C) Ionization energy exceeds the energy of incident electrons
D) All of the above
Answer: D) All of the above

6. Which of the following factors does NOT affect the breakdown voltage of a gas?
A) Pressure
B) Temperature
C) Frequency
D) Current
Answer: D) Current

7. The phenomenon of corona discharge is most likely to occur when:
A) Conductors are closely spaced
B) Conductors are far apart
C) Voltage is low
D) Air humidity is high
Answer: A) Conductors are closely spaced

8. In a Van de Graaff generator, the voltage generated depends on:
A) Size of the generator
B) Type of insulation used
C) Radius of the metal sphere
D) All of the above
Answer: C) Radius of the metal sphere

9. Partial discharge in cables is an indication of:
A) Overload condition
B) Insulation failure
C) Short circuit
D) Ground fault
Answer: B) Insulation failure

10. Which technique is used to measure very high voltages accurately?
A) Voltage dividers
B) Digital multimeters
C) Capacitive voltage transformers
D) Wheatstone bridges
Answer: A) Voltage dividers

11. The breakdown voltage of solid insulation is affected by:
A) Moisture content
B) Temperature
C) Voltage stress
D) All of the above
Answer: D) All of the above

12. The purpose of surge arresters in a high voltage system is to protect against:
A) Overvoltage
B) Overcurrent
C) Undervoltage
D) Undercurrent
Answer: A) Overvoltage

13. Which material is commonly used as a dielectric in high voltage capacitors?
A) Air
B) Paper
C) Mica
D) Oil
Answer: D) Oil

14. The breakdown strength of a dielectric material is measured in:
A) Ohms
B) Amps
C) Volts per meter
D) Farads
Answer: C) Volts per meter

15. The main cause of corona loss in high voltage transmission lines is:
A) Insufficient conductor spacing
B) High humidity
C) Impurities in the insulating material
D) High conductor temperature
Answer: A) Insufficient conductor spacing

16. Which of the following is a fundamental requirement for good insulation in high voltage systems?
A) Low dielectric constant
B) High dielectric strength
C) Low resistivity
D) High thermal conductivity
Answer: B) High dielectric strength

17. The insulation resistance of a high voltage cable is measured in:
A) Ohms
B) Megohms
C) Farads
D) Amperes
Answer: B) Megohms

18. A corona ring is used to:
A) Protect against lightning strikes
B) Reduce corona loss
C) Improve conductor flexibility
D) Increase conductor diameter
Answer: B) Reduce corona loss

19. Which method is used to extinguish the arc in a high voltage circuit breaker?
A) Increase the voltage
B) Reduce the current
C) Increase the current
D) Reduce the voltage
Answer: D) Reduce the voltage

20. Which parameter is critical in determining the safe operating voltage of a high voltage insulator?
A) Diameter
B) Length
C) Leakage current
D) Creepage distance
Answer: D) Creepage distance

21. Which type of insulator is commonly used in high voltage transmission lines?
A) Glass
B) Porcelain
C) Rubber
D) PVC
Answer: B) Porcelain

22. Which material is often used as a filler in high voltage cables to improve insulation properties?
A) Aluminum
B) Copper
C) Lead
D) Steel
Answer: C) Lead

23. The main advantage of gas-insulated substations (GIS) over conventional substations is:
A) Lower cost
B) Smaller footprint
C) Higher reliability
D) Higher efficiency
Answer: B) Smaller footprint

24. Which type of transformer is used to increase the voltage for long-distance transmission in high voltage systems?
A) Step-up transformer
B) Step-down transformer
C) Isolation transformer
D) Auto-transformer
Answer: A) Step-up transformer

25. What is the approximate breakdown voltage of dry air at atmospheric pressure?
A) 3 kV/cm
B) 10 kV/cm
C) 30 kV/cm
D) 100 kV/cm
Answer: B) 10 kV/cm

26. Which device is used to measure the magnitude and polarity of DC voltages in high voltage systems?
A) Electrostatic voltmeter
B) Digital multimeter
C) Oscilloscope
D) Wattmeter
Answer: A) Electrostatic voltmeter

27. The term “breakdown voltage” refers to the voltage at which:
A) Current becomes zero
B) Conductor melts
C) Insulation fails and current starts to flow
D) Dielectric constant becomes infinite
Answer: C) Insulation fails and current starts to flow

28. Which phenomenon is responsible for power loss in high voltage transmission lines due to ionization of air?
A) Dielectric breakdown
B) Corona discharge
C) Electromagnetic interference
D) Capacitive coupling
Answer: B) Corona discharge

29. Which property of a material determines how well it resists the flow of electric current?
A) Permittivity
B) Conductivity
C) Susceptibility
D) Impedance
Answer: B) Conductivity

30. What is the primary function of surge capacitors in a high voltage system?
A) Store electrical energy
B) Smooth voltage fluctuations
C) Protect against lightning surges
D) Regulate power factor
Answer: C) Protect against lightning surges

31. Which type of material is preferred for high voltage cables to minimize losses?
A) Copper
B) Aluminum
C) Silver
D) Gold
Answer: A) Copper

32. The breakdown voltage of a gas decreases with:
A) Decrease in temperature
B) Increase in pressure
C) Decrease in humidity
D) Increase in frequency
Answer: D) Increase in frequency

33. Which parameter is crucial in determining the efficiency of corona rings?
A) Shape
B) Material
C) Size
D) Color
Answer: C) Size

34. What is the primary purpose of a bushing in a high voltage transformer?
A) Insulation
B) Cooling
C) Voltage regulation
D) Noise reduction
Answer: A) Insulation

35. The insulation of underground cables is commonly protected with:
A) PVC sheath
B) Rubber sheath
C) Lead sheath
D) Aluminum sheath
Answer: C) Lead sheath

36. The phenomenon of flashover occurs when:
A) Voltage exceeds the dielectric strength of air
B) Insulation fails catastrophically
C) Electric field strength is too low to ionize air
D) Conductor temperature exceeds critical limit
Answer: A) Voltage exceeds the dielectric strength of air

37. Which technique is used to measure the dielectric constant of insulating materials?
A) Impulse testing
B) Tan delta measurement
C) Breakdown testing
D) Capacitance measurement
Answer: D) Capacitance measurement

38. Which device is used to detect and locate faults in high voltage cables?
A) Wattmeter
B) Megger
C) Oscilloscope
D) Multifunction tester
Answer: B) Megger

39. The power loss in a high voltage transmission line due to corona effect depends primarily on:
A) Voltage level
B) Current flow
C) Frequency of operation
D) Distance between conductors
Answer: A) Voltage level

40. The breakdown voltage of liquid dielectrics is generally higher than that of gases because:
A) Liquids have lower permittivity
B) Liquids can absorb more heat
C) Liquids can self-heal
D) Liquids have higher molecular density
Answer: D) Liquids have higher molecular density

41. Which parameter is critical in determining the withstand voltage of insulators in high voltage systems?
A) Surface area
B) Conductivity
C) Creepage distance
D) Temperature coefficient
Answer: C) Creepage distance

42. Which type of insulator is commonly used in high voltage bushings?
A) Pin type
B) Suspension type
C) Shackle type
D) Solid core type
Answer: A) Pin type

43. Which material is commonly used as an arc quenching medium in high voltage circuit breakers?
A) Air
B) Oil
C) Water
D) SF6 gas
Answer: D) SF6 gas

44. The breakdown strength of a solid insulator is primarily dependent on:
A) Temperature
B) Pressure
C) Voltage gradient
D) Moisture content
Answer: C) Voltage gradient

45. Which phenomenon is undesirable in high voltage systems due to its potential to cause radio interference?
A) Breakdown
B) Corona discharge
C) Flashover
D) Arcing
Answer: B) Corona discharge

46. Which technique is used to test the insulation strength of high voltage cables over a long period?
A) Impulse testing
B) Tan delta testing
C) Partial discharge measurement
D) Aging test
Answer: D) Aging test

47. Which material is commonly used as an insulating varnish in high voltage applications?
A) Epoxy
B) Silicone
C) Polyethylene
D) PVC
Answer: A) Epoxy

48. The breakdown voltage of a gas increases with:
A) Decrease in pressure
B) Decrease in temperature
C) Increase in humidity
D) Increase in electrode gap
Answer: B) Decrease in temperature

49. Which property of a material is crucial for determining its suitability as an insulator?
A) Thermal conductivity
B) Permeability
C) Permittivity
D) Perfusion
Answer: C) Permittivity

50. What is the purpose of a surge diverter in high voltage systems?
A) Prevent overcurrent
B) Regulate voltage
C) Protect equipment from lightning surges
D) Improve power factor
Answer: C) Protect equipment from lightning surges

High Voltage Engineering MCQs

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