Electrical test
Moisture in oil (Karl Fischer)
Measurement of water content in transformer oil by Karl Fischer titration — moisture is one of the main accelerators of insulation ageing.
The Karl Fischer test measures the water content of transformer oil in parts per million. Moisture lowers the oil's dielectric strength and is one of the strongest accelerators of paper insulation ageing, so controlling it is central to extending a transformer's life.
Water enters a transformer through ageing of the cellulose, breathing and leaks, and it is damaging on two fronts: it lowers the dielectric strength of the oil, raising the risk of breakdown, and it accelerates the irreversible ageing of the paper insulation. Karl Fischer titration quantifies that water precisely, in ppm, on an oil sample.
The number alone is not enough: moisture migrates between oil and paper with temperature, so the same transformer reads differently hot and cold. The result is therefore interpreted together with the oil temperature at sampling and, ideally, expressed as relative saturation, which tells how close the oil is to its water-holding limit. Most of the water in an aged transformer lives in the paper, not the oil, and the oil reading is the accessible window into it.
At TEVKO the Karl Fischer analysis is run in an accredited laboratory and interpreted under references such as IEC 60814 and the oil-condition guidance of IEEE C57.106, alongside the dissolved gas analysis and physicochemical tests. When moisture is high, the path forward — oil reconditioning, filtering or a transformer drying process — is defined with data, and verified by re-measurement.
What the moisture test supports
Dielectric-strength protection
Detects water lowering the oil's breakdown voltage before it causes a failure.
When it applies: Routine oil condition monitoring and before re-energizing.
Paper-life protection
Flags moisture accelerating cellulose ageing, triggering reconditioning or drying.
When it applies: Ageing assets and units with breathing or sealing issues.
How we run the test
Sampling
Oil sample taken with the transformer in service, recording oil temperature at sampling.
Laboratory analysis
Water content quantified by Karl Fischer titration in an accredited laboratory.
Interpretation
Read with temperature and relative saturation, alongside DGA and physicochemical results.
Action & protocol
Documented report; if needed, reconditioning/filtering or drying is defined and verified by re-measurement.
Frequently asked questions — moisture in oil (karl fischer)
Why is moisture in transformer oil a problem?
Water lowers the dielectric strength of the oil (raising breakdown risk) and strongly accelerates the irreversible ageing of the paper insulation. Controlling moisture is one of the most effective ways to extend a transformer's service life.
How is moisture in oil measured?
By Karl Fischer titration on an oil sample, giving the water content in ppm. It is run in an accredited laboratory, typically alongside dissolved gas analysis and the physicochemical oil tests.
Why is temperature important when interpreting moisture?
Because water migrates between oil and paper with temperature, so the same transformer reads differently hot and cold. The result is interpreted with the sampling temperature and, ideally, as relative saturation — how close the oil is to its water-holding limit.
What is done if moisture is too high?
Depending on the level and where the water resides, the options are oil reconditioning or filtering and, when the paper is wet, a transformer drying process. The action is defined with data and verified by re-measuring the moisture afterward.
Moisture in oil (Karl Fischer) in images
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