Importance of Buchholz Relay for Transformer in Power Safety

What Is a Buchholz Relay for Transformer?

A Buchholz relay is a gas‑ and oil‑operated protection device installed in the pipe that connects the main transformer tank to the conservator (expansion) tank in oil‑immersed transformers. It detects abnormal conditions inside the transformer—such as insulation breakdown, winding faults, hot spots, core heating, and rapid oil movement caused by severe internal arcing—before catastrophic failure occurs. When gases produced by fault energy accumulate in the relay chamber, or when a surge of oil flows rapidly during a major fault, the relay triggers an alarm and/or trips the transformer circuit breaker.

Where It’s Installed

The relay is mounted in the oil pipe between the main tank and the conservator so it can sense both gas collection (slow‑developing faults) and sudden oil flow (serious internal faults). Proper mounting angle and oil level are critical for sensitivity.

How a Buchholz Relay Works: Two‑Stage Protection

Most Buchholz relays contain two floats (or a float + vane) and mercury switch / micro switch mechanisms:

1. Gas Accumulation Stage – Alarm:

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