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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