Physical Fundamentals of Insulation Design for Low-voltage Equipment

For several years, insulation coordination for low voltage equipment has been an important concern of several international committees. The reports 664 and 664A of the International Electrical Commission (IEC) gave the basis for thorough investigations in 1980 and 1981. In cooperation between USA and Germany, a large field test of electrical insulations has been carried out. About 30000 insulators have been observed for several years under various voltages. Insulation resistance and electrical strength were measured and have provided x lo6 data points up to now. Research groups at the University of Darmstadt and Erlangen took over the task of evaluating these results by using statistical methods. In parallel, at the University of Erlangen an intense research program has been carried out, in order to quantify the influence of insulating materials, environmental conditions and design of the insulating systems on the long term insulation behavior. The final results of the statistical evaluations and the research program were elaborated in a working group of the German national standards committee. They are intended to support the drafting of scientifically founded, revised standards on insulation coordination in the IEC.