Buchholz relay
The Buchholz relay , also known as Buchholz protection , is an electrical protective device in liquid-insulated power transformers as well as choke coils with expansion vessels . It was developed in 1921 by the engineer Max Buchholz . The Buchholz relay indicates errors such as electrical short circuits , interturn short circuits or a lack of transformer oil . In the case of minor errors, this state is only reported, the so-called Buchholz warning, and in the case of high-current errors such as short circuits, the transformer or choke coil is automatically switched off as part of the Buchholz tripping to prevent destruction.
Mode of action
In liquid-cooled transformers, insulation faults or severe overloads lead to local overheating at an early stage, which causes gas to develop in the transformer. The gas bubbles collect in the upper part of the housing and displace the insulating liquid. In the event of small errors, a float is lowered and a switch is activated to report the error. In the case of large errors, a sudden overpressure occurs, which causes a strong flow of insulating fluid. This opens a switch with the help of a storage flap, which immediately switches off the transformer and thus protects it from further damage. This switch also switches if too much gas accumulates in the relay or if too much oil is lost.
The Buchholz relay is usually located in the pipeline to the expansion tank . The Buchholz relays usually have a connection for a copper pipeline on the upper cover of the housing, which in turn is laid further to a location on the transformer that is accessible from the outside without danger. The operator of the transformer can take a gas analysis there from time to time. The gas analysis can be used to determine which insulating material has gasified in the transformer. This valve is also used to take oil samples. A connected gas sampling device can also be used for checking from the ground. Depending on the requirements, the Buchholz relay has a flange or threaded connection. The classic Buchholz relay must comply with the requirements of the EN 50216-2 standard. The EN50216-2 standard replaces the old DIN 42566: 1989-03 . Depending on the requirements, the Buchholz relay is equipped with up to four (2 per float) break or changeover switches, which either send an alarm signal or ensure that the transformer is switched off. With newer Buchholz relays, the float movement is transmitted by magnets and reed switches in order to be able to guarantee precise switching. There is one magnet in each float.
The Buchholz relay is one of the area of network protection in electrical energy supply systems .
Specialist literature
- Günter Springer: Expertise in electrical engineering. 18th edition, Verlag - Europa - Lehrmittel, Wuppertal, 1989, ISBN 3-8085-3018-9
- Réne Flosdorff, Günther Hilgarth: Electrical energy distribution. 4th edition, Verlag BG Teubner, 1982, ISBN 3-519-36411-5
- Gerhard Kiefer, Herbert Schmolke: VDE 0100 and practice, guide for beginners and professionals . 14th edition. VDE Verlag GmbH, Berlin, Offenbach 2011, ISBN 978-3-8007-3284-5 , p. 492, 493 .
