Buchholz relay

Most large oil-filled transformers contain a Buchholz relay to detect abnormalities within the transformer, any abnormalities may trigger an alarm or send a trip signal.

In the field of electric power distribution and transmission, a Buchholz relay, also called a gas relay or a sudden pressure relay, is a safety device mounted on some oil-filled power transformers and reactors, equipped with an external overhead oil reservoir called a conservator. The Buchholz Relay is used on conservator type oil preservation systems as a protective device sensitive to events which occurs during dielectric failure inside the equipment.

When an electric arc or overheating develops inside the coils, gas is generated. The relay has two different detection modes. On a slow accumulation of gas, due perhaps to slight overload, gas accumulates in the top of the relay and forces the oil level down. A float operated switch in the relay is used to initiate an alarm signal. This same switch will also operate on low oil level, such as a slow oil leak. If an arc forms, gas accumulation is rapid, and oil flows rapidly into the conservator. This flow of oil operates a switch attached to a vane located in the path of the moving oil. This switch normally will operate a circuit breaker to shut down (isolate) the apparatus before the fault causes additional damage. Buchholz relays have a test port to allow accumulated gas to be withdrawn for testing. Flammable gas found in the relay indicates some internal fault such as overheating or arcing, whereas air found in the relay may only indicate low oil level or a leak. Buchholz relays have been applied to large power transformers at least since the 1940's.

The relay was first developed by Max Buchholz in 1921.

Names like beechwood relay or beech relay are a sign of a botched translation from German manuals.

External links

• Buchholz relay technical specifications from Electromotoren und Gerätebau Barleben GmbH Contains a detailed description (in English) of the Buchholz detection principles and mechanisms

• Koncar A.k.a Rade Koncar , buchholz relays , for power and distribution transformers.

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• Buchholz Relay