Insulating Fluid Condition: check transformer oil tests against IEC 60422:2024 or IEEE C57.106-2015
Insulating Fluid Condition is a free Seetalabs® tool for maintenance engineers, laboratories and asset managers. Enter the results of an oil test and the tool finds the table of limits that applies to your fluid, standard, equipment and Um, classifies each property and shows which one sets the headline result. It runs in your browser.
How it works
- Describe the liquid and its use. Choose the fluid (mineral oil, natural ester from soybean, rapeseed or sunflower, synthetic ester, or silicone), the standard and the lifecycle state: in service, as delivered, or after filling, where the standard publishes that state. Then choose the equipment (main tank, on-load tap-changer, switchgear, bushing or instrument transformer) and enter Um.
- Check the table the tool will use. A short chain, "Which table of limits applies", goes from the liquid to the standard, the state, the equipment and Um, and ends with the table and category in plain words. Options that change the limits, such as an inhibited oil or the tap-changer connection, sit just below it.
- Enter one or more samples. Each sample has a date, a temperature and the properties you have. Every property is optional: an empty field is not evaluated and never becomes zero. A value reported as below the detection limit, written "<x", is evaluated at x only where a lower value is better; elsewhere the row is shown as not classifiable.
- Read the result. Each property shows its band, its trend and the number of samples behind it. A summary gives the property that sets the headline, then a dossier answers the questions in order: is the liquid fit for service, which symptom groups appear, what to do and when, where the water is (oil or paper), how each property is moving, and how the same sample reads under the other in-service standards for that fluid.
You can save your inputs to a JSON file on your own computer, open it again later and print the result.
Method and standards
The limits come from the standard you select. For mineral oil the tool carries IEC 60422:2024, IEC 60422:2013 and IEEE C57.106-2015. For natural esters it carries IEC 62975:2021 and IEEE C57.147-2018; for synthetic ester, IEC 61203:2025; for silicone, IEC 60944:1988 and IEEE C57.111-1989. Each row cites the table and page it comes from, for example "IEC 60422:2024 Table 5, Cat A, row BDV".
IEC standards give Good, Fair and Poor bands per property. The tool applies the edges as printed: the Good edge is strict and the Fair edge is inclusive. IEEE C57.106-2015 gives one continued-use limit per property, so the result is Class I, when every limit you entered is met, or "Not Class I". The standard assigns Class II or III on a composite evaluation (clause 4.2.1); the tool shows which properties fail and leaves that evaluation to you.
The headline is the band of the worst scored property. It points you to the property that needs attention first; it is not an overall verdict on the liquid, because the standards set limits and actions per property, not for the liquid as a whole.
Water is handled in three ways. For mineral oil sampled at 20 °C or above, the tool converts water content to 20 °C with IEC 60422:2013/COR1 Formula A.1. It converts water content to relative saturation and classifies it with IEC 60422:2013 Table A.1 for mineral oil, whichever IEC 60422 edition you chose, because the 2024 edition gives relative saturation classes only for online monitoring (Table B.1). Natural esters use IEC 62975:2021 Table A.2. Paper moisture in equilibrium with the oil is shown for information; Moisture & Loading Capability takes that question further.
Treatments follow the symptom groups of IEC 60422:2024 Table 10: physical, chemical, additives and corrosive sulphur. Re-inhibition is offered only for mineral oil and only when acidity and interfacial tension allow it. CIGRE TB 962 §5.7.7 adds an early-reclamation flag, for example at acidity of 0.10 mg KOH/g or more even while the band is still Good. For a passivated oil under IEC 60422:2013, a passivator loss above 10 mg/kg per year, computed from your samples, moves the row to Fair, as corrected by CIGRE TB 625. The next sample date comes from IEC 60422:2013 Table 4, with a confirmation sample when a property is Poor.
Trends are a Seetalabs® choice, declared on the page: a least-squares slope over the dated samples and a straight-line projection to the next band edge, never beyond 20 years.
Mineral-oil limits (IEC 60422:2024, IEC 60422:2013, IEEE C57.106-2015) and the synthetic-ester table of IEC 61203:2025 were checked cell by cell against the standards. For natural esters under IEC 62975:2021 and for silicone, the rows cite their table and clause and are marked as cited rather than checked. Where a band edge is our reading of the table, the row says so. The status is shown in the information panel of each row.
Worked example: one sample, three standards
The example ships with the tool. A generator step-up transformer, mineral oil, inhibited, main tank, Um 245 kV, sampled four times between 2020 and 2026. The latest sample, taken on 14 April 2026 at 52 °C, reads:
| Property | Value |
|---|---|
| Breakdown voltage | 58 kV |
| Water content | 16 mg/kg |
| Acidity | 0.13 mg KOH/g |
| Dissipation factor at 90 °C | 0.13 |
| Interfacial tension | 23 mN/m |
| Colour | 3 |
| Oxidation inhibitor remaining | 22 % of the original content |
Under IEC 60422:2024, the tool selects Table 5, Category A. The headline is Poor, set by the oxidation inhibitor: 22 % is below the 40 % edge of the Fair band. Breakdown voltage, water, acidity, dissipation factor, interfacial tension and colour are all Fair. Across the four samples, interfacial tension is falling and reaches Poor within two years on the current slope, and water has risen. The treatment suggested for the chemical symptoms is reclamation, then re-inhibition; reconditioning alone is not suggested. Because one property is Poor, the next step is a confirmation sample.
Under IEC 60422:2013, the headline is again Poor on the inhibitor. Colour is shown but not scored, because this edition treats it as a qualitative property.
Under IEEE C57.106-2015, for 230 kV and above, the result is "Not Class I". Acidity of 0.13 mg KOH/g, Fair under IEC 60422:2024, exceeds the IEEE continued-use limit of 0.10, and interfacial tension of 23 mN/m is below the IEEE limit of 32.
The same sample is Poor under one standard because of the inhibitor, and Not Class I under another because of acidity and interfacial tension. The tool shows all three readings side by side, with the table behind each one, so the choice of standard is visible in the result rather than hidden in it.
A check you can repeat by hand: 10 mg/kg of water measured at 40 °C corresponds to about 4.5 mg/kg at 20 °C with IEC 60422:2013/COR1 Formula A.1, the example given in the standard.
Limits
The tool gives an indication for planning, not a diagnosis and not an overall verdict on the liquid. It does not choose between Class II and Class III under IEEE C57.106-2015. It groups properties by the symptom groups of IEC 60422:2024 Table 10 but does not deduce the degradation mechanism behind them. The sampling interval comes from IEC 60422:2013 Table 4 also when you select the 2024 edition. Paper moisture is not estimated for tap-changers, switchgear or bushings. Trends need at least two dated samples. A result built on a single sample, or on a single property outside its limits, carries a warning.
Frequently asked questions
Why does the same oil sample pass one standard and fail another?
Each standard has its own table, categories and edges. In the example above, acidity of 0.13 mg KOH/g is Fair under IEC 60422:2024 Category A and exceeds the IEEE C57.106-2015 limit of 0.10 for 230 kV and above. The tool shows the table used for each reading.
Which edition of IEC 60422 sets the relative saturation class?
For a laboratory sample of mineral oil, the tool uses IEC 60422:2013 Table A.1 with either edition, and says so. On that table 20 % relative saturation is "wet". The 2024 edition classifies relative saturation only for online sensors (Table B.1), where 20 % is still Fair.
What happens to a value reported as "<0.05"?
The tool keeps the detection limit. Where a lower value is better, it evaluates the row at the limit, which is the cautious reading. Where the limit cannot decide the band, the row is shown as not classifiable instead of being set to zero.
Are the ester and silicone limits checked against the standards?
Mineral-oil limits and the IEC 61203:2025 synthetic-ester table were checked cell by cell. Rows for natural esters under IEC 62975:2021 and for silicone cite their table and are marked as cited, not checked; each row shows its status.
Related tools
- Moisture & Loading Capability: from the same water result, estimate paper moisture, the bubble inception temperature and the emergency load the unit can carry.
- Paper Insulation Remaining Life: thermal ageing scenarios for the paper, from a measured DP or the age, moisture and load.
Following oil results across a fleet
The tool reads one transformer at a time, and nothing is kept once you close the page. Ronin AI applies the IEC 60422:2024 limits to the oil tests of every transformer and turns an out-of-limit result into a dated action with a planning cost. Tell us how many units and how often their oil is tested.
The tool runs entirely in your browser. Its content security policy blocks every network connection (connect-src 'none'), so the values you enter are not sent to Seetalabs® or to anyone else, and nothing is stored in the browser. Your inputs leave the page only if you save them to a file yourself.
Tool version 1.0.5. Seetalabs®.
