Electric Strength

The dielectric strength of insulating media must be higher than the electric stress under all possible conditions. Unfortunately, dielectric strength is often subject to significant statistical variations. Therefore, the fundamentals of statistics are considered at first. If the electrical strength is insufficient, discharges occur. They are treated separately depending on the type of insulating medium: Gas discharges can be well described in terms of physics, occur at comparatively low field strengths and show very different manifestations in uniform and non-uniform fields, on surfaces, in cavities or in the atmosphere. In other media, much higher dielectric strengths are often possible, but they depend on a large number of parameters. Special attention is paid to discharge processes in liquids, solids and vacuum. So-called partial discharges that do not lead directly to breakdown are especially important for the erosive ageing of insulating materials and for the diagnosis of insulation systems under applied voltage.