How Is a Duval Triangle Used to Diagnose a Transformer?

Published 27 Aug 2026Updated 27 Aug 20266 min readAdvancedDiagnostics

Quick answer — The Duval triangle (Triangle 1) plots the three hydrocarbon fault gases — methane (CH4), ethylene (C2H4) and acetylene (C2H2) — as percentages on a triangular map, and the area the point falls in indicates the fault type: partial discharge, thermal faults of rising temperature, or electrical (arcing) faults. It is a simple, widely used diagnostic tool alongside certain gas ratios.

Contents

The method
What the zones mean
Using it with other tools

How does the Duval triangle diagnose a transformer fault?

The method

Take the relative percentages of CH4, C2H4 and C2H2 from the DGA (normalising these three to 100%), then plot on the Duval triangle. The region identifies the fault category.

What the zones mean

Low-energy zones point to partial discharge; mid zones to thermal faults (hot spots, overheating, cellulose); high-acetylene zones to electrical arcing. The temperature level of a thermal fault is inferred from the ethylene/ethane ratio.

Using it with other tools

The triangle is a fast classification, but it should be combined with the gas ratios (Duval ratios, Rogers, Doernenburg), the rate of change, and oil/insulation tests to build a complete picture.

References & standards

IEC 60599
IEEE C57.104

Book series Academy

Related manufacturers

Prolec GE (GE Vernova) · Prolec GE Waukesha · Hitachi Energy USA · Siemens Energy · Eaton · Virginia Transformer Corp

Related components

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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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