Paper Insulation Remaining Life: thermal ageing scenarios to DP 200
Paper Insulation Remaining Life is a free Seetalabs® tool for asset managers and maintenance engineers. From a measured DP or the age, water in oil, oil preservation and load, it computes thermal ageing scenarios for the paper to DP 200 under IEC 60076-7:2018 Annex A. From 2-FAL it gives an estimated DP range, never years.
How it works
The tool walks you through five steps.
- Transformer. Age, liquid, paper (kraft, thermally upgraded, aramid or not known), oil preservation (free-breathing or sealed) and cooling mode. If you want a scenario at your own load, add the top-oil rise, the hot-spot gradient and the ratio R from the heat-run test; there are no default values.
- Paper condition today. A DP measured on a paper sample is the starting point. Without it, the tool starts from new paper and the age. 2-FAL results give, separately, an estimated DP and, with two or more dated analyses, its trend in DP per year.
- Moisture and oxygen. Water in oil with the sampling temperature, or a known paper moisture. The tool finds the paper moisture and the columns of IEC 60076-7:2018 Table A.1 that bracket it. Oxygen from the DGA is shown for information.
- Load and ambient. None, a constant load, or a 24-hour profile. Without a load, only the reference case is computed.
- Result. Thermal ageing scenarios to DP 200 (or 150, or 250), as a range of years labelled "scenario, not a forecast", a table of the four conditions of Table A.1 showing what drying or sealing would change, and a chart of DP over time.
You can save your inputs to a JSON file on your own computer, open it again later and print the result.
Method and standards
Relative ageing rate. IEC 60076-7:2018 §6.3: Equation 2 for kraft paper, with V = 1 at 98 °C, and Equation 3 for thermally upgraded paper, with V = 1 at 110 °C. For kraft paper in transformers built to IEEE 55 °C rise, the tool offers the IEEE C57.91-2011 Annex D basis, with the reference at 95 °C.
Hot spot. The difference equations of IEC 60076-7:2018 §8.2.3 with the constants of its Table 4, or one of three thermal models from the open-source IEEE C57.91 code (BSD-3-Clause), ported to the browser. The port was checked against the official Python code on its three example profiles: hot spot within 0.1 to 0.7 °C away from load steps, loss of life within 3 %.
Ageing of the paper. Chain-scission rates from IEC 60076-7:2018 Annex A, Table A.1, averaged over the hot-spot series. The table gives four conditions: free from air at 0.5, 1.5 and 3.5 % paper moisture, and with air at 0.5 %. The tool uses only those four, with no interpolation between them and no combination of moisture and air. The standard itself declares these values unconfirmed (§6.2 NOTE 1), which is one more reason every output is a range.
Scenario years. Years to DP 200 = (1/DP end − 1/DP today) / (k × 8 760), where k is the chain-scission rate per hour. The range runs from the lowest DP today at the fastest applicable rate to the highest DP today at the slowest. For a free-breathing unit, or paper moisture above 3.5 %, Table A.1 gives only an upper bound, and the tool writes "at most".
Paper moisture. From water in oil through the saturation curves of IEC 61203:2025 and IEC 62975:2021 (Table A.1), then the oil-paper equilibrium curves of IEC 61203:2025 Figures A.2 and A.3, read from the graphs; or entered directly.
Furans. 2-FAL is converted to an estimated DP with the four models of IEEE C57.140-2017 (Equations 7 to 10: Chendong, De Pablo, Pahlavanpour, Shkolnik), as a range over the models relevant to the paper type. The estimated DP is never a starting point for years.
Checks against the standards. The tool's test suite reproduces IEC 60076-7:2018 Table 1 exactly, Table A.2 within 3 %, and the full worked example of Annex I; and IEEE C57.91-2011 Tables 1 and 2, §5.3 and Annex I (DP 200 after about 150 000 h at V = 1). One cell of IEC 60076-7:2018 Table A.2 does not match its own formula; the test documents it as a probable misprint.
Worked example: a measured DP, then furans alone
Case 1, measured DP. A 30-year-old transformer with kraft paper and a sealed conservator. A paper sample gives DP 500, and paper moisture is 1.5 %. No load is entered.
Only one column of Table A.1 applies: free from air, 1.5 % moisture. In the reference case the hot spot stays at 98 °C, where V = 1. The chain-scission rate is k = A × exp(−EA / (R × 371 K)), about 1.43 × 10⁻⁷ per hour. The scenario is (1/200 − 1/500) / (k × 8 760), about 2.4 years to DP 200.
That number describes a paper held at 98 °C every hour of the year. A transformer loaded below its rating runs cooler, so for that unit the reference case gives a shorter life than the real one. To see the difference, enter the heat-run data and the load. With a top-oil rise of 52 K, a hot-spot gradient of 26 K and R = 6, a constant 1.0 p.u. at 20 °C ambient gives a 98 °C hot spot and the same 2.4 years. At a constant 0.8 p.u. the hot spot is about 78 °C and the same paper reaches about 25 years in the scenario.
Case 2, furans alone. Kraft paper, no age and no measured DP. Two 2-FAL analyses: 0.3 ppm in May 2020 and 1.5 ppm in May 2026.
The tool gives an estimated DP of about 625, with a range of 381 to 684 across the De Pablo, Pahlavanpour and Chendong models, and a trend of about 22 DP per year. It gives no years. To compute a scenario it asks for a measured DP or the age of the transformer.
Limits
The scenarios cover the cellulose paper in oil, not the whole transformer. Aramid paper is outside the models, and the tool says so. Ester and silicone liquids use the mineral-oil data of IEC 60076-7:2018, declared on the page. The hot spot is the hottest point of the winding: most of the paper is cooler and ages more slowly. Past drying, oil treatments, overloads and faults are unknown to the model unless the analyses reflect them. Methanol and ethanol markers are not included, and the Stebbins furan model is not implemented. The result is an indication for planning, not a diagnosis.
Frequently asked questions
Why does the tool not turn 2-FAL into years?
Furans give an average condition of the paper, and the models disagree: in the example above the same 2-FAL gives an estimated DP between 381 and 684 across three IEEE C57.140-2017 models. Years also need the hot spot, moisture and oxygen, which furans do not carry. The tool therefore reports the DP range and its trend only.
Why is the reference scenario so short?
The reference case of IEC 60076-7:2018 holds the hot spot at the temperature where V = 1: 98 °C for kraft paper, 110 °C for thermally upgraded paper. Few transformers run there all year. Enter the heat-run values and your load to get a scenario for your duty.
What would drying or sealing change?
The result includes the four conditions of IEC 60076-7:2018 Table A.1 side by side. Moving from 3.5 % to 1.5 % moisture, or from air to a sealed conservator, changes the chain-scission rate, and the table shows the scenario for each condition.
Related tools
- Moisture & Loading Capability: estimate paper moisture from a dielectric response test or from the oil, and see how it limits emergency loading.
- Insulating Fluid Condition: check the oil test results, water included, against the table of limits for your fluid and equipment.
Following paper condition across a fleet
The tool looks at one transformer and keeps nothing once you close the page. For a fleet, Ronin AI imports the laboratory reports, shows the DP range estimated from 2-FAL for every sample next to the gas results and their trend, and turns the findings into an Action Plan for an engineer to review. As in this tool, 2-FAL never becomes years. Tell us how many transformers have furan results.
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 1.1.2. Seetalabs®.
