Previous Year Question
Correct answer: B
Explanation
In a three-wire system, two properly connected phase overcurrent relays are sufficient to detect any inter-phase fault because any line-to-line fault involves at least one of the two monitored phase-current combinations. Therefore option B is correct.
Formula
Step-by-step solution
Correct Answer
B — Two
Concept and Reasoning
In a three-wire system, two properly connected phase overcurrent relays are sufficient to detect any inter-phase fault because any line-to-line fault involves at least one of the two monitored phase-current combinations. Therefore option B is correct.
Calculation / Key Relation
Minimum phase-fault OC elements in a 3-wire system: 2
Exam Takeaway
Two phase relays can cover all inter-phase faults in a three-wire system.
Common Mistake
Do not assume one relay per phase is always the minimum required arrangement.
Common mistake
Do not assume one relay per phase is always the minimum required arrangement.
Exam tip
Two phase relays can cover all inter-phase faults in a three-wire system.
Quick method
Two phase relays can cover all inter-phase faults in a three-wire system.