Bucholz Relay provides Mechanical Protection for Transformer.

What is a Buchholz Relay?

  1. It is a Oil and gas actuated Protection Relay for Mechanical Protection of the Transformer  against incipient fault occurring inside the transformer, such as impulse breakdown of the insulating oil, insulation failure of turns etc.
  2. It is placed in the pipe connecting transformer tank to the conservator.
  3. It is generally used in large oil immersed transformers (rated more than 500 kVA). 

      What is the Working Principle of Buchholz Relay?

      1.Accumulation Of Gases:

      Whenever a fault occurs inside the transformer, such as Arcing, Partial Discharge, Insulation failure of turns, breakdown of core or excess core heating, the fault is accompanied by production of excess heat. This excess heat decomposes the transformer insulating oil which results in production of gas which tends to flow in upward direction towards conservator and hence collected in the buchholz relay.

      These Gases accumulate in the upper part the Buchholz container which causes fall of oil level in it i.e. lowering the position of float and thereby tilting the mercury switch. The contacts of this mercury switch are closed and an alarm circuit energized.

       2. Severe Winding Fault:

      In case of Serious Faults, there is high Oil flow from the main Transformer Tank to the Conservator. Switch is operated, and therby Tripping the Transformer.

        How to test the Buchholz Relay?

        1. Put the bucholz relay in the Test Mode and short the alarm contacts and check if the annunciation is received in the control room, then short the tripping contact and check whether Trip command is issued to the breaker.
        2. Inject air into the relay from the pet valve provided at the top of the relay, to simulate gas accumulation and check the alarm and tripping.
        3. Drain the oil from the relay after closing the gate valves provided at both the sided of the relay in the connecting pipeline and check the annunciation and tripping