Expert Tribology Consultancy
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Turn a Karl Fischer water reading and a top-oil temperature into relative saturation (%RS), the ppm equivalent at 20 °C, the free-water temperature and an estimated paper moisture — per IEC 60422:2024, IEC 61203:2025 and IEC 62975:2021.
22 ppm at 70 °C
300 ppm at 20 °C
200 ppm at 50 °C
35 ppm at 40 °C (IEC 60422 Table 6 star-point row)
Liquid saturation Ws(T) = 10^(A10 − B10/(273.15+T)) uses the IEC harmonised averaged-literature coefficients (Table A.1, identical across IEC 61203:2025 and IEC 62975:2021). Relative saturation is %RS = 100·ppm/Ws(T); water activity is temperature-invariant, so %RS trends are comparable across sample temperatures while the raw ppm is not. The free-water temperature inverts the saturation equation at 100 %RS. Estimated paper moisture (%WCP) is interpolated from the digitised IEC 61203:2025 Annex A equilibrium figures (Kraft paper only) and is presented as approximate, with its confidence and caveats. Condition bands cite IEC 60422:2024 (%RS Annex B Table B.1 — applied only when the %RS is declared as measured by a continuous online sensor, the table’s printed scope; ppm Table 5, and Table 6 for the Cat F tap-changer rows — one per OLTC winding connection) and IEC 62975:2021 (ester %RS, Annex A Table A.2).
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 1.2 · 30-09-2026. What changed, and when
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