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Electric Motor Overhauling

Understanding How Vacuum Pressure Impregnation (VPI) Works

Leaving your electric motor or generator to deteriorate on their own over a long period of time will eventually lead to a failure in your equipment.

And in due time, turning a blind eye to this issue will even cause your business to crumble slowly.

While equipment failure is bound to happen over time, there are still certain precautions one can take to slow down a potential breakdown or even prevent it. In this case, for equipment like electric motors or generators, Vacuum Pressure Impregnation (VPI) can be put to good use.

What is it

Vacuum Pressure Impregnation (VPI) is a process which makes use of vacuum and pressure to completely seal porous materials with resin or varnish. Also known as a type of electric motor overhauling, it is used for a range of electrical components, such as high voltage stators, armatures and rotors to fill up gaps and achieve a void-free impregnation.

The process


The equipment is first placed into an oven which will heat up the equipment and let the moisture start evaporating. With this step, the resin will be able to penetrate the material in a finer way.

Dry vacuuming

The engineer will then proceed to take out the equipment from the oven and have it placed inside the dry impregnation chamber, removing air and any leftover moisture. From there, the vacuum is applied and will only reach to a stop once the prearranged setpoint is attained.


Afterwards, the resin will be introduced into the chamber, coating the part and ensuring all the gaps and pores in the equipment is completely filled up.

Wet vacuuming

For the wet vacuum and pressure cycle, the vacuum levels will simply be released and the engineer will hold it for a fixed period of time.


At this step, the engineer will vent the pressure, drain out the excess resin from the chamber and remove the equipment.


Last but not least, curing of the resin is done by heating the equipment up in the oven for one final time.

Advantages of VPI

Now that you have understood the process of VPI, you should move on to understand why it is beneficial for you.

  • Protection from hostile conditions, namely: water, vibration, dust and heat
  • Excellent bond strength
  • Gives a composite dielectric structure
  • Enhanced thermal conductivity
  • Practical in terms of cost
  • A solid and stronger structure which can withstand: moisture, leaks, corrosion, cracks
  • Increased winding strength
  • Seals up insulation against catastrophic conditions
  • Increase in life expectancy of motor and generator windings

From time to time, your equipment, be it electric motor, generator or switchgear will need to have routine checks done on them. While VPI remains as one of the most important repair services, generator rewinding does not have to be limited to just that.

In fact, keep exploring and you’ll find many other types of services which can be done on your equipment.

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