Insulation co-ordination 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 664 A of the International Electrical Commission (IEC) provided the basis for thorough investigations. In cooperation between the USA and Germany a large field exposure of electrical insulations has been carried out. About 30000 insulations under various voltages have been observed for several years. Insulation resistance and electrical strength were measured, and have yielded up to now about 10 million pieces of data. The author´s research group at the University of Erlangen took over the task of evaluating these results using statistical methods. In parallel, an intense research program has been carried out to quantify the influence of insulating materials, environmental conditions, and the design of the insulating systems on the long-term insulation behavior. The results of the statistical evaluations and the research program are under discussion in the German national standards committee. They are intended to support the drafting of scientifically founded revised standards on insulation coordination in the IEC