The Insulation Resistance of Capacitors After Long-Time Electrification

In recent months design engineers have been interested in capacitors with extremely high values of insulation resistance not normally achieved in the common one- or two-minute electrification period. After long periods of electrification, insulation resistance values in the order of 100-million megohm microfarads and more can be achieved with some types of capacitors. Such high values can be accurately measured by the special measuring technique described in this paper, which also discusses the interpretation of test data taken at various temperatures and voltages on some typical Mylar capacitors. The concepts of instantaneous and equivalent parallel insulation resistance are developed and their significance discussed.