How Are the DGA Gas Ratios Interpreted?
Quick answer — The gas ratios compare pairs of key gases to classify a fault. Common approaches are the Rogers ratios (e.g. CH4/H2, C2H2/C2H4, C2H4/C2H6), the Doernenburg ratios, and the Duval triangle, which assign a fault type — partial discharge, thermal (of rising temperature), or electrical (arcing). The ratios are used with the absolute values and the trend, and the diagnosis guides the next step. Different interpretations exist for mineral oil, ester and other cases.
Contents
How do you interpret the DGA gas ratios?
The ratios
Rogers uses CH4/H2, C2H2/C2H4, C2H4/C2H6; Doernenburg uses CO2/CO, CH4/H2, C2H2/C2H4, C2H4/C2H6; each assigns a fault type by the ratio bands.
The categories
The ratios separate partial-discharge, thermal faults (low/high temperature) and arcing (electrical) faults.
Using it
Apply the ratio method, combine it with the absolute gas values and the trend, and verify with an inspection; use the correct interpretation for the fluid (oil or ester).
References & standards
- IEC 60599
- IEEE C57.104
Related
Related manufacturers
Prolec GE (GE Vernova) · Prolec GE Waukesha · Hitachi Energy USA · Siemens Energy · Eaton · Virginia Transformer Corp
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