Buchholz Relay

Used in transformers with conservator, it is placed in a main pipe between conservator and main tank. Buchholz relay is a gas trap, with floats that detects bubbles from a transformer failure.

The purpose of this device is to protect the oil-immersed transformer when the following types of failures are originated:

  • Slow generation of gas in the transformer due to the low energy failures.
  • High generation of gas due to the high energy failures.
  • Oil loss through leakage.
  • Sudden pressure changes by high energy failures.


  • Structure with two tubes, located on top and bottom, inside a cubicle called oil chamber
  • The floats have a mercury switch; these are closed when the float rotates, when space in the cubicle is occupied by a gas product of the failure the oil is moved out.
  • There are two stages, when the first float located on top goes down, contacts are closed and the alarm works, the next phase is caused by accumulation of gases in cubicle actuates the second float, activating the trigger signal or when a sudden power failure occurs forcing the movement of the oil.
  • Connection scheme ANSI, IEC.

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