How Is Moisture Measured in a Transformer?
Quick answer — Moisture in a transformer is measured in the oil (water content in ppm, often by Karl Fischer titration) and inferred in the insulation (paper) by dividing the oil moisture by the partition coefficient. High moisture lowers dielectric strength and accelerates aging, so it is a key condition indicator. Online moisture sensors and oil sampling both track it.
How is moisture measured in a transformer?
Measuring in oil
A sample is titrated (Karl Fischer) to give the water content in ppm. The value is compared against limits for the oil and loading.
Moisture in the paper
The paper holds most of the moisture; the oil/paper partition coefficient is used to estimate the total. The balance shifts with temperature, so the interpretation depends on the temperature.
Why it matters
Moisture lowers the breakdown voltage, causes partial discharge and accelerates paper aging (and can release water at high temperature). Keeping the unit dry extends the insulation life.
References & standards
- IEC 60599
- IEEE C57.104
Related
Related manufacturers
Prolec GE (GE Vernova) · Prolec GE Waukesha · Hitachi Energy USA · Siemens Energy · Eaton · Virginia Transformer Corp
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Technical content is prepared from engineering references, standards frameworks, manufacturer documentation and industry sources. Contractual or compliance decisions should refer to current official standards. TransformerPath Technical Editorial.
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