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B-Stage vs. VPI Insulation Systems for 13.2KV/13.8KV Large Electric Motors


Higher voltage (Medium voltage) Insulation systems have been developed over many years, with a recent interest in newer vacuum pressure impregnation (VPI) insulation systems that have a perception of being newer and better but not with an improvement in longevity or quality. The newer VPI insulation systems today are promoted by some manufacturers and vendors as being better than the older systems that have lasted for the last 50+ years with great success. The main reason for the VPI processing of newer design large motors is for economics. The newer motors are smaller in physical size and have higher temperature rises. The use of VPI in these motors allows the manufacturer to reduce costs for manufacturing purposes… but not necessarily for longevity. This trend has now been incorporated into older machines with the same reasons: for lower costs to process but not necessarily for longer lasting service. 

Insulating Electric Motors: VPI or Varnish Dip?


VPI (Vacuum Pressure Impregnation) is a process that is a technological step forward from varnishing electric motors. The old dip and bake (in varnish) method of "insulating" motors is replaced by the VPI process for specific reasons:

  1. Harsh Environment
  2. Improved Efficiency (through better heat transfer)
  3. Improved Mechanical Winding Design

When electric motor repairs proceed as normal, a special VPI insulation system is used on the coils in place of standard insulation. The (preheated) Stator or Rotor is lowered into the VPI pressure chamber and a vacuum is drawn. A resin with 0% solvents is entered into the chamber, pressure is applied, then the submerged unit becomes entirely impregnated with resin creating a virtually "void free" insulation system.

This "void free" insulation system drastically reduces motor failure for three reasons:

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