Buchholz Relays - definition

The Buchholz Relay is a mechanical safety sensor, used in hermetically sealed oil transformers, mounted in the cable connecting the transformer's hull to the oil conservator. Its primary purpose is the early detection of internal faults in the transformer before they lead to serious failures. It works by detecting gases and disturbances in the flow of insulating fluid that accompany abnormal phenomena such as arcing, local overheating or internal short circuits.

Inside the Relays Enclosures there are floats and flip-flops that react to the presence of gases and directional oil flow. The formation of gases due to degradation of insulation or sparking causes them to accumulate in the Relays space, leading to the float dropping and closing the corresponding alarm contact. In the event of a stronger phenomenon, e.g. a rapid oil flow caused by a severe short circuit, a lever is actuated to interrupt the main power circuit, resulting in the immediate disconnection of the transformer.

The Buchholz Relay only works in transformers with a maintainer, as its operation is based on the presence of free gas and liquid flowing between the tanks. Due to its simple design and reliability, it is widely used as a safety component in commercial and industrial power generation. Analysis of the gases collected in the Relays chamber also provides valuable diagnostic information on the type and location of a fault in the transformer insulation system.

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