Zero-Sequence Reference and Phase Voltage

Correct Answer

A — Both Assertion and Reason are true and Reason is the correct explanation of Assertion.

Concept and Reasoning

For an L-L fault there is no zero-sequence current, so the zero-sequence network is not fixed by current flow. At open-circuited generator terminals this can leave the common zero-sequence voltage reference indeterminate even though line-to-line voltages remain uniquely determined. Hence both assertion and reason are true and the reason explains the assertion: option A.

Calculation / Key Relation

L-L fault: I0=0

line voltages are independent of common zero-sequence voltage shift

Exam Takeaway

A common phase-voltage shift cancels in line-to-line voltages.

Common Mistake

Do not infer that indeterminate phase reference makes line voltage indeterminate.