The useful life of plastic power cables with particular emphasis on the influence of humidity

The cause of cases of damage resulting from the influence of humidity and electric fields in the polythene branched structures affected, the so-called water-trees, were studied. During this period (over ten years) several cable designs were developed with various protecting measures, as well as considerable efforts made towards improving the insulating materials and also to develop special materials less sensitive to water-trees. The published results of the investigations already indicate a considerable improvement of the materials and cable designs and in several fields there are also positive experiences in practical service. The resulting range of solutions and alternatives make the choice more difficult for the cable manufacturer, but particularly so for the user. The Datwyler company has performed long-term tests in order to select the most suitable material design for the insulation and to offer the highest possible operating reliability for the user. These tests have been largely completed and have produced results which can be clearly evaluated. The tests still in progress are only intended to provide better explanations of supplementary phenomena. The author summarises the most important findings