What Does a Buchholz Relay Detect and How Does It Trip?
Quick answer — A Buchholz relay senses gas accumulation and oil surge in the pipe between the transformer and the conservator. A slow gas accumulation (from a minor fault) gives an alarm; a large gas or oil surge (from a major fault) trips the transformer. The gas can be collected and analysed to diagnose the fault. It is fitted on oil-filled units above a certain size.
How does a Buchholz relay operate?
What it senses
It has a gas (and sometimes a surprise) element and an oil-surge element. Gas collects under the relay from a minor fault and gives a low alarm; a violent fault causes gas and an oil surge that trips the unit.
Alarm vs trip
Slow gas accumulation trips the alarm and flags a developing fault; a major gas or surge trips the breaker to disconnect the transformer, protecting it.
Diagnosis
The collected gas is analysed (combustible, CO2, etc.) and the DGA used to identify whether it is a thermal, partial-discharge or arcing fault.
References & standards
- IEC 60076-1
- IEEE C57.12.90
Related
Related manufacturers
Prolec GE (GE Vernova) · Prolec GE Waukesha · Hitachi Energy USA · Siemens Energy · Eaton · Virginia Transformer Corp
Related components
Technical content is prepared from engineering references, standards frameworks, manufacturer documentation and industry sources. Contractual or compliance decisions should refer to current official standards. TransformerPath Technical Editorial.
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