Directional induction type over current relay is used for protection of

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This question was previously asked in

WBPSC JE Electrical 2018 (Held on 18th Feb 2018) Official Paper

Answer 1

Directional overcurrent relay

A directional overcurrent relay is used for the protection of ring main distribution lines.
Ring main distribution lines are the lines that exist in an interconnected system with two or more sources.
In such a system, the directional overcurrent relays are usually connected with a trip of an incoming line breaker for fault current flow that can flow back to the source.
Directional overcurrent relays respond to excessive current flow in a particular direction in the power system.

Construction of the direction induction type of overcurrent relay

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The relay typically consists of two elements. One is a directional element, which determines the direction of current flow with respect to a voltage reference.
And the other element is non-directional which detects the fault current and isolates the system from the fault.
The driving torque is produced due to the interaction between the directional and the non-directional element of the relay.