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Vacuum Pressure Impregnation or VPI: What is It?

08/20/2020

You've got a electric motor in for repair and the repair shop indicates that your problem lies in the windings. Maybe when you are reviewing the quote you see the acronym VPI in connection with the rewinding process.

Before you sign off on the repair, you want to know what is involved with VPI or Vacuum Pressure Impregnation, and whether its a smart choice for your motor. If that's you, you've found the right place.

Why Motor Winding Insulation is Important

Insulation of motor windings / coils serves three key purposes:

  • Insulate the windings from potential contaminants (electrical and physical)
  • Dissipate heat generated by the windings
  • Make the windings rigid and secure

These are all vital for efficient operation of your electric motor.

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

06/08/2016

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?

05/19/2016

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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