Buchholz Relay

 

What is Buchholz Relay?

A Buchholz relay is a safety device mounted on (some) oil-filled power transformers and reactors, equipped with an external overhead oil reservoir called a “conservator”. Buchholz relays are used as a protective device, as they are sensitive to the effects of dielectric failure that can occur inside the equipment they protect. Buchholz relays are a type of gas detection relay.

Buchholz relays have two main elements. The upper element consists of a float. The float is attached to a hinge in such a way that it can move up and down depending upon the oil level in the Buchholz relay container

A mercury switch is fixed on the float. The alignment of the mercury switch hence depends upon the position of the float.

The lower element consists of a baffle plate and a mercury switch. This plate is fitted on a hinge just in front of the inlet (main tank side) of the Buchholz relay in a transformer in such a way that when oil enters in the relay from that inlet in high pressure the alignment of the baffle plate along with the mercury switch attached to it, will change.

Buchholz relay


In addition to these main elements, a Buchholz relay has gas release pockets on top. The electrical leads from both mercury switches are taken out through a molded terminal block.

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