In many items of high voltage plant such as transformers and cables, oil and paper is still used as the dielectric medium. In newer installations, especially underground transmission cables, a polymeric material is preferred. Much of this equipment was installed several decades ago with little thought as to its environmental impact or the associated decommissioning costs. Supergen, a project running for several years aims to redress this balance and look at more sustainable ways of distributing and producing electricity. The current project part of Supergen V: Asset Management and Performance of Energy Systems (Amperes) is looking at alternative materials and technologies that are more sustainable and recylable. The project has two major facets looking at solid and liquid insulation systems.
Solid insulation systems
Whilst crosslinked polyethylene (XLPE) is an excellent material for high voltage cables having excellent dielectric, thermal and mechanical properties, it does suffer from one major disadvantage; it is not easily recyclable. This facet of the project is looking into alternative, recyclable materials to replace XLPE in high voltage cables for the medium to long term. Polyethylenes, ethylene vinyl acetate co-polymers and propylene co-polymers have so far been considered. A realistic balance between good dielectric, mechanical and thermal properties using materials with a reasonable cost is sought.Liquid insulation systems
Whilst paper and copper can be readily recycled, the same is not true of the conventional mineral oils used in high voltage plant. Such oils are generally toxic and present a significant environmental hazard both in service and at ultimate disposal. This facet of the project is looking at alternative recyclable oils for high voltage applications. So far, dodecylbenzene and a range of different vegetable oil systems have been considered from the point of view of their ageing behaviour. A recyclable oil having the good properties of mineral oil but without the environmental drawbacks at a reasonable cost is sought.