Safety and environment-related objections to high-voltage transformers being located in urban areas could be overcome by an oil-free technology developed by ABB.
The transformer, called Dryformer, uses windings of cross-linked polyethylene (XLPE) cables rather than paper-insulated conductors submerged in oil.
Oil is used in high-voltage transformers for both insulation and dielectric cooling.
Electricity can be most efficiently distributed at high voltages. But fears over oil leaks and fire hazards have prevented their installation in urban or environmentally sensitive areas.
The XLPE cables used in the Dryformer have a circular cross-section, as opposed to the traditional rectangular section. This reduces stress and associated losses.
`Corners produce a high stress in every field of engineering,’ said professor Mats Leijon, inventor of the Dryformer. `In magnetics they produce heat, vibration and losses. In Dryformer we have spread the stresses over a larger surface. We’ve got rid of the corner to make the flux path easier.’
XLPE cables were invented in the late 1960s but have only recently been used for transformer windings with the Powerformer, launched by ABB last year.
The Dryformer can be configured in shapes that are impossible for traditional transformers as its windings do not have to be contained in an oil bath. Its other advantage is that the cable can be wound straight from a drum to speed up repairs and maintenance.
ABB has already developed a 10MVA, single-phase prototype unit at its Ludvika facility in Sweden.
The first commercial-scale Dryformer rated at 20MVA, will be installed at a Swedish hydropower plant in the autumn as a generator step-up transformer.
Copyright: Centaur Communications Limited