BUCHHOLZ Tesar — Buchholz Relay Trip (Gas Detection)
At a glance
- Severity
- E STOP
- Domain
- CABINA_ELETTRICA
- Reference standard
- IEC 60076-1, IEC 60076-3
- Product / context
- Tesar oil-immersed transformer — Buchholz relay on conservator pipe, stage 1 gas alarm / stage 2 oil-flow trip
What it means
The Buchholz relay, installed on the pipe between the transformer and the oil conservator, has detected gas presence or abnormal oil flow. Stage 1 (alarm) indicates slow gas accumulation due to partial discharges or local overheating. Stage 2 (trip) indicates a severe internal fault with rapid gas production or violent oil displacement, typical of inter-turn short circuit or internal arcing.
Probable causes
- Partial discharges in insulation due to oil or paper degradation
- Inter-turn winding short circuit
- Internal electric arc due to dielectric breakdown
- Low oil level allowing air into the relay (false alarm)
- Excessive mechanical vibrations transmitted to the relay (false trip)
Reference values
| applicabilita | Oil-immersed transformers only |
|---|---|
| stadio 1 allarme | Slow gas accumulation (>200 cm³), typically combustible gases |
| stadio 2 trip | Rapid oil flow (>0.7 m/s) indicates severe internal fault |
| gas tipici | H2 (partial discharges), C2H2 (arcing), C2H4 (hot spot >700°C), CO (cellulose degradation) |
| pressione intervento | Pressure relief valve at 0.5-0.7 bar |
Where to start
Work per CEI 11-27 (qualified person only). Before any intervention apply the 5 golden rules: disconnect, secure against reclosing, verify absence of voltage, earth and short-circuit, delimit the work area. DO NOT reset immediately. Check which stage operated: stage 1 (alarm, gas accumulation) or stage 2 (trip, oil flow)?
Full guided diagnosis in the app
The diagnostic tree for this fault has 5 guided steps with measurements, checks and resolutions. You'll find it in ElectraIQ, one of the five IndexOS apps: free, works offline.
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More Tesar codes
- PT100 / T1-T2 — Transformer Overtemperature