A Buchholz relay sits in the pipe from the main tank of an oil-filled transformer to the conservator. Slow gas from overheating or minor arcing collects in the relay and lowers a float to raise an alarm, while a violent internal fault drives an oil surge that swings a flap and trips the transformer. Gas drawn from the relay can be tested to tell trapped air from fault gases such as hydrogen and acetylene.
Buchholz alarm on T1 overnight and there's gas in the window, take a sample and get a DGA before anyone talks about re-energising it.
Also heard as
- gas relay
- 63
Related terms
86 relay
Lockout relay that latches after a serious trip and holds breakers open until someone resets it by hand.
Differential protection
Scheme that compares current entering and leaving a protected zone and trips when the two disagree.
OLTC
On-load tap changer: a transformer switch that changes the turns ratio under load to regulate voltage.