How do you work the buchholz relays?

Answer 1

A Buchholz relay is used to provide protection for Transformers. It will detect a drop in a transformer's oil level, as well as a minor or major breakdown of insulation within the transformer. The first stage of Buchholz relay's operation is an alarm; the second stage acts to disconnect the transformer.

The Buchholz relay is located in the inclined tube that connects the top of a transformer with the oil expansion tank located above the transformer. It is a rectangular, hollow, vessel, containing two pivoted floats, each containing a Mercury switch. The lower float is also fitted with a deflection baffle.

If the oil level falls, then the upper float will pivot downwards and its mercury switch will initiate an alarm inside the substation building. If the oil level continues to drop, then the lower float will pivot downwards, and its mercury switch will initiate a protective relay which will disconnect the transformer.

Minor insulation breakdown between windings will generate a gas. This gas will collect inside the top of the relay, causing the upper float to lower, and its mercury switch will initiate an alarm in the substation. This gas can be collected, if necessary, via a stopcock at the top of the relay, allowing it to be analysed to determine its nature, which will then indicate the likely source of the fault.

A major insulation breakdown, or explosion, will send an oil shock wave through the relay, causing the lower float's baffle to deflect the float downwards, initiating the protection system which will disconnect the transformer.

A Buchholz relay looks after itself, and doesn't require you to 'work it'!