Buchholz relay

The Buchholz relay, also called Buchholz relay is an electrical protective device in the oil-insulated power transformers. It was developed in 1921 by the engineer Max Buchholz. The Buchholz relay indicates errors such as short circuits, winding shorts or even lack of transformer oil. For small errors, this condition is only reported, the so-called Buchholz warning, and high-current faults such as short circuits, the transformer automatically shut off (Buchholz trip), so it is not destroyed.


In oil-cooled transformers insulation fault or overload strong lead early on to local overheating, which causes a release of gas in the oil chamber of the transformer. The gas bubbles collect in the upper part of the housing and displace the oil. For small faults, thereby reducing a swimmer and a contact is closed, the signals the error. For large errors result is a sudden pressure, which causes a strong flow of oil. Wherein a switch is opened by means of a slide ram, which switches off immediately the transformer and protects against further injury.

The Buchholz relay is usually located in the oil connection line to the expansion tank. Usually have the Buchholz relay to the upper cover of the housing has a connection for a copper tube, which in turn is moved further to a place on the transformer, which is accessible from the outside without any risk. There may be from the operator of the transformer from time to time a gas analysis are removed. With the help of gas analysis can be analyzed, which has gassed insulation in the transformer.

The Buchholz relay counts in electrical power systems to the area of ​​power system protection.


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Pictures of Buchholz relay