Expert Tribology Consultancy
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Advanced transformer fault analysis using dissolved gas analysis
Zone convention: the PD, T1, T2, T3, D+T zones and the outer boundaries of D1 and D2 are the published IEEE C57.104-2019 zones (Table 6, printed p. 42; Figure 3, p. 41). That guide prints seven zones and contains no arcing-in-paper partition. This tool additionally splits D1 into D1-H/D1-P and D2 into D2-H/D2-P to distinguish arcing in oil (-H) from arcing in paper insulation (-P), following Duval & Buchacz, "Gas Formation from Arcing Faults in Transformers — Part II", IEEE Electrical Insulation Magazine 38(6), Nov/Dec 2022, whose sub-zone summits are printed on p. 15 and drawn in Figure 1, p. 13. The split does not move any IEEE C57.104-2019 boundary: D1-H together with D1-P is exactly C57.104's D1, and D2-H together with D2-P is exactly its D2. The sub-zones are the authors' proposal, derived from 61 inspected cases, and the paper states they are "not an official rule or an obligatory regulation". The authors further note that points close to the right-hand boundary of D2-P should be attributed to D2-P or D2-H only with caution, because of possible overlaps, and that an arcing-in-paper reading should preferably be confirmed by other evidence — acoustic tests, furans, or the CO₂/CO ratio, the last of which is often misleading in sealed equipment.
TriboTech's Duval Triangle tool includes all seven Duval triangle variants in a single interface, covering mineral oil, non-mineral fluids and on-load tap changer diagnostics. Triangle 1 carries the arcing sub-zones D1-H, D1-P, D2-H and D2-P published by Duval and Buchacz (2022), and an optional OC zone for oil contamination from OLTC gases, published by Bustamante et al. (2024).
All seven Duval triangle variants, from primary mineral oil to natural ester (e.g. FR3)
Arcing sub-zones D1-H/D2-H and D1-P/D2-P, separating arcing in paper from arcing in oil: published for Triangle 1 by Duval & Buchacz (2022); Triangle 3b carries them for alternative fluids on the authors' unpublished coordinates
Optional zone for oil contamination from OLTC gases in mineral oil transformers (Bustamante et al. 2024)
The tools are calculation tools made available free of charge by TriboTech ApS as part of the professional communication of its engineering consultancy. The tools perform a calculation based on the values entered and the published methods identified. They do not constitute an examination of an asset, a diagnosis, or advice on any specific asset. The tools have no knowledge of the asset's design, history, loading or operating conditions, and a result cannot therefore serve on its own as the basis for a technical or operational decision. A result is an indication, not a diagnosis. Use of the tools does not create a client relationship and does not create an advisory relationship. TriboTech ApS provides advisory services only under a concluded framework agreement, and no advisory liability is assumed for the use of results from the tools outside such an agreement. Any decision taken on the basis of a result — including a decision not to act — is taken by the user on the user's own professional judgement and at the user's own risk. As CIGRE itself puts it: "Actual actions on the equipment are the sole responsibility of engineers in charge of the transformers" (CIGRE Technical Brochure 771, 2019, section C.8, printed page 54). Each tool states which published methods and which editions the calculation is based on. The standard itself is the authoritative source, and a standard may have been revised since the edition a tool uses.
Method implementation — The calculation behind this tool is versioned. When a correction changes the result the tool gives for the same input, the version below changes with it. Version 1.28 · 10-10-2026. What changed, and when
Terms
There is no single Duval method. Which triangle or pentagon to use is decided by fluid, then equipment, then the question you are answering — a practical selection guide.
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How the two most-used graphical DGA methods actually work. Step-by-step ternary and pentagon arithmetic, the zone boundaries that came from inspected transformer cases, and when each diagram earns its place on a real diagnosis.
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The geometry behind the two most-used graphical DGA methods — barycentric projection for Triangle 1 and an area-weighted polygon centroid for Pentagon 1. Step-by-step derivations, worked examples, and the deliberate asymmetry in how the zones are defined.
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In a non-vacuum load tap changer, acetylene and hydrogen are the normal signature of the device doing its job — not a fault. Here is why applying main-tank DGA frameworks to LTC oil raises false alarms, and how to interpret an LTC sample properly.
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