How Is a Transformer Insulation Dried?
Quick answer — Transformer insulation is dried to remove moisture, which lowers the dielectric strength and accelerates aging. Drying methods include hot-oil circulation, vacuum drying, and for large units a low-frequency or vapour-phase drying (with a hot solvent). The goal is to reduce the moisture in the paper to a safe level (e.g. well below 2%) before the unit is recommissioned, verified by moisture/DP measurement.
How is transformer insulation dried?
The problem
Moisture in the insulation lowers the breakdown voltage, causes partial discharge and accelerates aging; insulation should be kept dry by design and by the breather.
Drying methods
Hot-oil circulation, vacuum drying, or vapour-phase/low-frequency drying are used to drive the water out, often with a heated tank and a vacuum.
Verification
The success is verified by insulating resistance, power factor, moisture (oil and paper), DP, and sometimes a drying curve, before the unit is returned to service.
References & standards
- IEC 60076-1
- IEC 60599
Related
Related manufacturers
Prolec GE (GE Vernova) · Prolec GE Waukesha · Hitachi Energy USA · Siemens Energy · Eaton · Virginia Transformer Corp
Related components
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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