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SarkariResultOutAdditional Assistant Engineer (Electrical) · 2026

Previous Year Question

In the context of transformer protection, which of the following protection schemes is precisely designed to distinguish earth faults within the transformer windings, mainly in the star-connected primary side?
  1. Overcurrent Protection
  2. Overvoltage Protection
  3. Differential Protection
  4. Restricted Earth Fault (REF) Protection

Correct answer: D

Explanation

REF protection is a sensitive unit protection for earth faults within the defined zone of a star-connected winding and its neutral CT arrangement. It is more sensitive to internal earth faults than ordinary overcurrent protection.

Step-by-step solution

Restricted Earth Fault Protection explanatory diagram

Correct Answer

D — Restricted Earth Fault (REF) Protection

Explanation

REF protection is a sensitive unit protection for earth faults within the defined zone of a star-connected winding and its neutral CT arrangement. It is more sensitive to internal earth faults than ordinary overcurrent protection.

Key Concept

Restricted Earth Fault Protection

Exam Point

REF = sensitive earth-fault protection inside a restricted transformer zone.

Exam tip

REF = sensitive earth-fault protection inside a restricted transformer zone.

Quick method

REF = sensitive earth-fault protection inside a restricted transformer zone.