ELANTAS Electrical Insulation

Frequently Asked Questions

How do I vacuum pressure impregnate (VPI)?

Conditions of VPI processing depend on the type of resin used in the process. The two cases below are the most common.

CASE 1 - Epoxy

  • Preheat unit to remove moisture and thermoset any B-staged materials. Time and temperature will depend upon individual circumstances.
  • Cool unit to 49 - 54°C (120 - 130°F).
  • Place unit in vacuum tank. Pull vacuum of 2 - 3 mm mercury for 30 minutes. For high voltage applications where additional layers of insulating tape are required, a reduced pressure of 0.5 mm mercury or less may be required, and increased vacuum time may be necessary to insure proper penetration and fill.
  • Admit the epoxy resin while maintaining vacuum. Completely cover coils. Hold vacuum for 10-15 minutes.
  • Break vacuum with dry nitrogen and apply 90 psi of pressure for 1 hour. For high voltage applications where additional layers of insulating tape are required, the pressure time should be lengthened. Usually, the time under 90 psi of pressure should be twice that of the time under vacuum.
  • Return resin to storage tank and drain unit for 20 - 30 minutes.
  • Cure unit in accordance with suggested bake cycle.


CASE 2 - Unsaturated Polyester in vinyl toluene

  • Preheat unit to remove moisture and thermoset any B-staged materials. Time and temperature will depend upon individual circumstances.
  • Cool unit to 49 - 54°C (120 - 130°F).
  • Place unit in vacuum tank. Pull vacuum of 1 - 3 mm of mercury for 30 minutes. For high voltage applications where additional layers of insulating tape are required, an increased vacuum time may be necessary to insure proper penetration and fill.
  • Admit the epoxy resin while maintaining vacuum. Completely cover coils. Hold vacuum at 7-10 mm of mercury for 10-15 minutes.
  • Break vacuum with dry nitrogen and apply 80 - 90 psi of pressure for 1 hour. For high voltage applications where additional layers of insulating tape are required, the pressure time should be lengthened. Usually, the time under pressure should be twice that of the time under vacuum.
  • Return resin to storage tank and drain unit for 20 - 30 minutes.
  • Cure unit in accordance with suggested bake cycle.