Properties and problems of polymer high voltage insulations

In cable insulations manufactured in bulk, weak spots lead to local field enhancements. Therefore the permissible voltage is not limited by the macroscopic field strength determined by the geometry but, for instance, by the local microscopic field strengths which occur on impurities and so on. If these reach the electric strength measured on ideal laboratory test samples, then the disruption begins there. As weak spots in fabrication can, in principle, only be avoided to a certain extent, a further gain in electrical stability is possible only by improvement of the material properties. For this it is useful to understand the intrinsic breakdown mechanism of the material