Q1. The main function of an insulator in an overhead transmission line is to:
A) Prevent leakage current
B) Provide mechanical support
C) Separate conductors from towers
D) Both B and C
Ans: D
Q2. The potential distribution along a string of suspension insulators is:
A) Uniform
B) Non-uniform
C) Linear
D) Exponential
Ans: B
Q3. The non-uniform voltage distribution in a string of suspension insulators is due to:
A) Capacitance between metal fittings and earth
B) Mutual capacitance between discs
C) Leakage resistance
D) All of the above
Ans: D
Q4. String efficiency increases when:
A) Line voltage increases
B) Number of discs decreases
C) Capacitance to earth is reduced
D) Capacitance between discs increases
Ans: D
Q5. String efficiency is defined as:
A) Ratio of voltage across top unit to total voltage
B) Ratio of total voltage to voltage across bottom unit × 100%
C) Ratio of total voltage to number of units
D) None
Ans: B
Q6. In a string of suspension insulators, the disc nearest to the line has:
A) Lowest voltage
B) Highest voltage
C) Equal voltage
D) Zero voltage
Ans: B
Q7. The use of grading rings helps in:
A) Equalizing potential distribution
B) Improving corona performance
C) Increasing string efficiency
D) All of the above
Ans: D
Q8. The string efficiency of a 3-disc string is generally around:
A) 100%
B) 90–95%
C) 60–70%
D) 40–50%
Ans: B
Q9. The capacitance between metal parts and earth is called:
A) Mutual capacitance
B) Shunt capacitance
C) Capacitance to earth
D) Series capacitance
Ans: C
Q10. A suspension insulator string has 4 discs; the bottom unit fails. The string voltage will:
A) Increase
B) Decrease
C) Remain same
D) None
Ans: A
Q11. Pin type insulators are generally used for voltages up to:
A) 11 kV
B) 33 kV
C) 66 kV
D) 132 kV
Ans: B
Q12. Beyond 33 kV, pin-type insulators are replaced by:
A) Strain type
B) Suspension type
C) Shackle type
D) Post type
Ans: B
Q13. The dielectric strength of porcelain is approximately:
A) 10 kV/mm
B) 30 kV/mm
C) 50 kV/mm
D) 5 kV/mm
Ans: B
Q14. The electric field in an insulator disc is maximum at:
A) Line end
B) Tower end
C) Middle
D) Uniform throughout
Ans: A
Q15. Which material is NOT used as an insulator?
A) Porcelain
B) Glass
C) Aluminium oxide
D) Copper
Ans: D
Q16. Shackle insulators are used in:
A) Overhead transmission lines
B) Distribution lines
C) Substations
D) Underground cables
Ans: B
Q17. The leakage distance of an insulator is the distance measured:
A) Along the shortest air path
B) Along the surface of the insulator
C) Between pin and conductor
D) None
Ans: B
Q18. The purpose of a creepage distance is to:
A) Prevent flashover under wet conditions
B) Increase mechanical strength
C) Decrease corona
D) All of the above
Ans: A
Q19. When an insulator string is cleaned or washed, its string efficiency:
A) Increases
B) Decreases
C) Unchanged
D) None
Ans: A
Q20. A voltage grading ring is placed:
A) Near the line end
B) Near the tower end
C) In the middle
D) Anywhere
Ans: A
Q21. The capacitance of each disc unit in a string is about:
A) 10–15 pF
B) 50–100 pF
C) 500 pF
D) 1 µF
Ans: B
Q22. Which insulator type can be used both as a strain and a suspension insulator?
A) Shackle
B) Disc
C) Pin
D) Post
Ans: B
Q23. In polluted environments, which insulator material is preferred?
A) Porcelain
B) Glass
C) Polymer (composite)
D) Wood
Ans: C
Q24. The corona discharge around insulators can cause:
A) Radio interference
B) Audible noise
C) Power loss
D) All
Ans: D
Q25. The potential distribution along the string can be made uniform by:
A) Grading rings
B) Capacitance control
C) Both A & B
D) None
Ans: C
Q26. The electric field intensity at the surface of a conductor depends on:
A) Shape
B) Size
C) Potential
D) All
Ans: D
Q27. The electric field around a conductor is highest at:
A) Sharp points
B) Flat surfaces
C) Uniform cross-sections
D) Cylindrical surfaces
Ans: A
Q28. The field intensity at a point due to a line charge varies as:
A) 1/r
B) 1/r²
C) r
D) Constant
Ans: A
Q29. The dielectric strength of air is about:
A) 3 kV/mm
B) 30 kV/mm
C) 10 kV/mm
D) 0.3 kV/mm
Ans: A
Q30. Electric stress control in cables and insulators is done using:
A) Grading
B) Shielding
C) Both
D) None
Ans: C
Q31. Potential distribution along suspension string becomes more uniform when:
A) Number of discs increases
B) Number of discs decreases
C) Capacitance to earth reduces
D) None
Ans: C
Q32. If string efficiency is 100%, then potential distribution is:
A) Uniform
B) Uneven
C) Exponential
D) None
Ans: A
Q33. Composite insulators are made of:
A) Epoxy resin core with silicone rubber sheath
B) Porcelain only
C) Glass only
D) Metal with ceramic coating
Ans: A
Q34. The main disadvantage of glass insulators is:
A) Brittleness
B) High cost
C) Low transparency
D) High weight
Ans: A
Q35. The height of pin-type insulators increases with:
A) Voltage
B) Frequency
C) Temperature
D) None
Ans: A
Q36. In an insulator, the dielectric loss depends on:
A) Frequency
B) Temperature
C) Both A and B
D) None
Ans: C
Q37. The leakage current over an insulator surface increases with:
A) Humidity
B) Pollution
C) Both
D) None
Ans: C
Q38. The main cause of flashover in polluted areas is:
A) Surface conductivity
B) Voltage variation
C) Wind
D) None
Ans: A
Q39. The capacitance grading method is used in:
A) Cable insulation
B) Transformer winding
C) Insulator strings
D) Both A and C
Ans: D
Q40. The ratio of maximum to average electric field intensity is called:
A) Field utilization factor
B) Efficiency factor
C) Voltage ratio
D) Power factor
Ans: A
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