On what basis is the insulation level of a 400 kV EHV overhead transmission line is decided?
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Answer & Explanation
Correct AnswerD. Switching overvoltage
Quick Explanation
At EHV levels such as 400 kV, switching surges become the dominant overvoltage for insulation coordination because their magnitudes relative to operating voltage and longer wavefronts can govern required clearances. Hence the insulation level is primarily decided by switching overvoltage: option D.
Formula / Key Relation
EHV insulation coordination is commonly governed by switching impulse withstand
Detailed Explanation
Correct Answer
D — Switching overvoltage
Concept and Reasoning
At EHV levels such as 400 kV, switching surges become the dominant overvoltage for insulation coordination because their magnitudes relative to operating voltage and longer wavefronts can govern required clearances. Hence the insulation level is primarily decided by switching overvoltage: option D.
Calculation / Key Relation
EHV insulation coordination is commonly governed by switching impulse withstand
Exam Takeaway
For EHV, think switching surge; for lower levels lightning often dominates.
Common Mistake
Do not assume lightning overvoltage governs insulation at every voltage class.
Quick Trick
For EHV, think switching surge; for lower levels lightning often dominates.
Common Mistake
Do not assume lightning overvoltage governs insulation at every voltage class.
Exam Tip
For EHV, think switching surge; for lower levels lightning often dominates.
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