Buchholz relay is

Question

Buchholz relay is

Examoogle · Accepted Answer

gas actuated device

Explanation: A Buchholz relay is a gas-actuated protective device installed in oil-immersed transformers to provide protection against internal faults. It is mounted in the pipe connecting the main transformer tank and the conservator tank.

Working Principle: During an internal fault, the arc produces heat, which decomposes the transformer oil into various gases like hydrogen, methane, and carbon monoxide. These gases collect in the upper part of the relay housing, displacing the oil and causing a float to tilt, which closes a contact to trigger an alarm or trip the circuit breaker.

Key Formulas: $V_{gas} \propto I^2_{fault} \cdot t$ — The volume of gas produced is roughly proportional to the square of the fault current and the duration of the arc.

Key Points: Used exclusively for oil-immersed transformers.; Capable of detecting both incipient (slow-developing) and severe internal faults.; Installed between the transformer tank and the conservator.; Operates in two stages: alarm for low-level gas and tripping for high-pressure gas surges.

Advantages: Detects incipient faults before they become catastrophic.; Simple and reliable operation.; Independent of electrical parameters like voltage or current magnitude.

Disadvantages: Cannot detect faults outside the main tank.; Risk of false operation due to mechanical vibration or oil replenishment.; Limited to oil-filled transformers only.

Applications: Oil-immersed power transformers.; Distribution transformers with a conservator tank.

Additional Info: Option A is incorrect because voltage sensitivity relates to relays like Over-voltage/Under-voltage relays.. Option B is incorrect because current sensitivity relates to Over-current or Differential relays.. The Buchholz relay is purely mechanical/physical (gas pressure) in its activation method.

Answer: D is correct — The Buchholz relay is a gas-actuated protective device specifically designed to detect internal faults in oil-immersed transformers.

Exam Tip: Always remember that Buchholz relays are NOT used for dry-type transformers, only for those with oil cooling/insulation systems.

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