Which of the following relay is used for the protection of feeder

SOLUTION

Differential relay:

• Differential relay operation depends on the phase difference of two or more electrical quantities.
• It works on the principle of comparison between the phase angle and the magnitude of the same electrical quantities.
• The differential relay is used for the protection of the feeder, large busbars, etc.

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Distance relay:

• Distance relay is widely used for the protection of high-voltage AC transmission line and distribution lines.
• Distance protection schemes are commonly employed for providing the primary or main protection and backup protection for AC transmission line and distribution line against three-phase faults, phase-to-phase faults, and phase-to-ground faults.

Under frequency relay:

• Under frequency relay is used to protect the alternator when the frequency drops below the operating frequency.
• It is a backup protection for over fluxing (V/F) protection.
• Under frequency occurs due to turbine low speed, grid frequency fluctuation, etc.
• The generator can tolerate moderate under frequency operation provided voltage is within an acceptable limit.

Buchholz relay:

• Buchholz relay protects the transformer from internal faults.
• It is the gas actuated relay.
• The Buchholz relay is placed between the main tank and the conservator.
• Buchholz relay is used in the transformer having a rating higher than 500KVA.
• It is not used in a small transformer because of economic considerations.