What Is VPI (Vacuum Pressure Impregnation)?
Quick answer — VPI (vacuum pressure impregnation) is a process that infuses the insulation of a winding (often dry-type) with a liquid resin by applying a vacuum to remove air and then pressure to drive the resin into the insulation. After curing, the winding is compact, sealed and moisture-resistant, with high mechanical and dielectric strength — common for cast-resin and VPI dry-type transformers.
What is VPI processing of a transformer?
The process
The winding is placed in a tank, a vacuum is applied to evacuate air and moisture, then the resin is introduced under pressure so it penetrates the insulation and fills the voids, and finally the unit is drained and cured (often with heat).
What it achieves
VPI yields a dense, void-free, moisture-resistant insulation system with improved dielectric, mechanical and thermal performance.
Applications
It is used for dry-type transformers, motors and reactors, and is an alternative to cast-resin where a robust, impregnated insulation system is needed.
References & standards
- IEC 60076-11 (dry-type)
- IEC 60076-1
Related
Related manufacturers
Prolec GE (GE Vernova) · Eaton · Virginia Transformer Corp · Delta Star · WEG Transformers USA · LS Electric America
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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