Chuck Yung
EASA Senior Technical Support Specialist

One of the most briskly debated issues in our industry is the comparison – and procedures for – vacuum pressure impregnation (VPI) versus dip & bake. For this article, I have expanded the discussion to include trickle epoxy and B-stage coils. Service centers that have a VPI tank will quickly point out the many benefits of VPI, such as better sealing of the windings and improved heat transfer from the winding conductors to the frame for enhanced heat dissipation.

Form and random windings have two distinctly different issues. For the form-wound machine, resin penetration is the biggest concern – giving a clear advantage to a VPI process. For random windings, the concern is retention of the resin.

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