Question

A protection system engineer is planning to provide complete protection for a 3-phase transmission line. He can achieve this by:

• A. Three phase fault relays and three earth fault relays
• B. Three phase fault relays and two earth fault relays
• C. Two phase fault relays and two earth fault relays
• D. Two phase fault relays and one earth fault relay

Hint:

To fully protect a 3-phase transmission line, you need both phase fault relays and earth fault relays for complete fault detection.

Answer 1

The Correct Option is D

To provide complete protection for a 3-phase transmission line, the protection system engineer should use:
- Two phase fault relays to protect the line against phase faults, and
- One earth fault relay to protect against ground faults.
This combination ensures that both phase-to-phase and phase-to-ground faults are adequately detected and protected against.
Thus, the correct answer is Two phase fault relays and one earth fault relay.