Vacuum Pressure Impregnated Transformers

VPI transformers, a new construction concept, are suitable for installations that require particular attention to the environment, with minimum flammable material.

The windings up to 1.1kV class are made in foil or strip in a continuous layer; for higher voltages, the winding is made of disks connected in series or parallel according to the voltage or power of the winding.

The insulation can be used in class F or H, and the impregnation is made with class H polyester resin

All production with air insulation has a small amount of flammable material, less of the resin solution and without any term of comparison with the oil solutions.

The transformer impregnated in air is not only suitable for distribution, but also for any type of special applications (such as the resin transformer). There are no particular limitations for the insulation levels, although generally it is not used for classes higher than 36 KV.

This type of transformer can be provided with a protective box, according to the desired IP. The boxes are painted with epoxy paint according to the RAL requested (RAL standard 7032) with pickled or galvanised sheet for outdoor installations.

Special applications for the outdoors include the creation of an aluminium box complete with MV ceramic bushing and LV resin insulators.

What is a vacuum-pressure impregnated transformer?

A vacuum‑pressure impregnated (VPI) transformer is a dry‑type transformer in which the winding pack is first vacuum‑dried to remove air and moisture and then impregnated under pressure with a class H polyester resin, creating a bonded, low‑flammability insulation that contains far less combustible material than oil‑filled units and is suitable for many distribution and special‑purpose applications.

How do vacuum-pressure impregnated transformers work?

The VPI process removes trapped air and moisture from the windings under vacuum, then forces resin into the winding under pressure so the resin fully penetrates and bonds conductor and insulation; once cured, this produces a mechanically stable, electrically insulating winding that resists vibration, partial discharge and moisture ingress while meeting thermal classes such as F or H.

What are the benefits of a vacuum-pressure impregnated transformer?

Key benefits include enhanced mechanical strength to withstand short‑circuit forces, superior moisture and pollution resistance, reduced fire risk because of minimal flammable content compared with oil solutions, and flexible thermal performance with class F or H insulation options; VPI units are also low‑maintenance and well-suited to environments where safety and longevity are priorities.

Where are vacuum-pressure impregnated Transformers used?

VPI transformers are used in commercial buildings, industrial plants, data centres and other critical installations where environmental safety, low flammability and reliable operation are essential; they can be supplied in protective enclosures to specified IP ratings and finished for outdoor use with MV ceramic bushings or LV resin insulators, typically up to insulation classes around 36 kV.