ABB has developed a high voltage transformer that does not need any oil for cooling or dielectric insulation. The new transformer, called Dryformer, will initially be available for primary voltages between 36 kV and 145 kV, and for power ratings up to 150 MVA.

Dryformer is air-cooled, with windings of dry polymer XLPE cable, rather than the paper-insulated conductors submerged in oil used in conventional high-voltage transformers. The XLPE cable technology was first applied to ABB’s high-voltage generator, Powerformer, launched in 1998.

The absence of oil has considerable benefits. There is no risk of ground or water contamination, and a greatly reduced risk of fire or explosion. Thomas Andersson, ABB Sales Manager for the Dryformer, said that he expected densely populated areas, underground facilities and ecologically sensitive areas to be primary markets for Dryformer.

Another advantage of Dryformer is that the electric field is totally contained within the XLPE cable, the surface of which remains at earth potential. This allows for optimization of the design in terms of electric and magnetic fields, mechanical forces and thermal stresses.

ABB Transformers has built a 10 MVA, single phase prototype unit at its facility in Ludvika, Sweden. The first full-scale Dryformer will be installed at a Swedish hydropower plant in autumn 1999.