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.
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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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