What is Buchholz relay?

The Buchholz relay: Buchholz relay is a protective device that is commonly used in oil-immersed transformers to detect internal faults and to prevent further damage. It is named after its inventor, Max Buchholz, a German engineer who developed the relay in 1921. The Buchholz relay is installed between the transformer tank and the oil conservator. It consists of a float chamber, a mercury switch, and a set of alarm and trip contacts. The float chamber is connected to the transformer tank and contains a float that is supported by a hinge mechanism. The float is designed to move up or down depending on the level of oil in the transformer tank. The operation of the Buchholz relay is based on the principle of gas detection. When an internal fault occurs in the transformer, such as a short circuit or insulation failure, it generates heat, which causes the oil to decompose and produce gases, mainly hydrogen and carbon monoxide. The gases rise to the top of the transformer tank and collect in the Buchholz relay float chamber. The increase in gas pressure causes the float to move downward, tilting the mercury switch and activating the alarm and trip contacts. The alarm contacts provide an audible or visual signal to alert the maintenance personnel of a fault. The trip contacts are used to disconnect the transformer from the power source to prevent further damage. The trip contacts may be connected to a circuit breaker or other protective devices. The Buchholz relay is a reliable and cost-effective means of protecting transformers against internal faults. It provides early warning of developing faults, such as slow oil leaks or insulation degradation, before they lead to catastrophic failure. It is widely used in oil-immersed transformers of all sizes and ratings and is an essential component of transformer protection schemes.