DIN EN 60243-2:2014-08

The internal electric stress of a non-homogenous test specimen under alternating voltage is determined by the mainly capacitive apparent impedance. If the direct voltage increases, the potential distribution might be mainly influenced by capacity, however, it depends on the voltage increase rate. Continuous stressing with direct voltage will result in the steady-state condition with conductive potential distribution. The selection between direct or alternating voltage depends on the testing purpose and, to a certain extent, on the intended use of the material. Loading with direct voltage will result in the following currents: capacitive current, current due to electric absorption (recharging effect), leakage current and, in some cases, the current resulting from partial dischargings. Additionally, the potential distribution in materials comprising layers of different insulation materials or being otherwise incosistent may also be influenced by charges of opposite polarity that accumulate on both sides of an interface due to interfacial polarization and are able to generate local fields of sufficient strength there to cause partial discharge and/or breakdown of the test specimens. For most materials, the value of the breakdown voltage due to loading with direct voltage is higher than the peak value of the alternating breakdown voltage. For most and in particular for non-homogenous materials, the breakdown voltage for direct voltage will be equal to or higher than three times the value for alternating voltage. In addition to the requirements of IEC 60243-1, this Part 2 of the International standard series IEC 60243 specifies further requirements for the determination of the electric strength of solid insulating materials when loaded with direct voltage and includes methods for the determination of breakdown voltages along the surface of solid insulation materials. The responsible committee is DKE/K 183 "Bewertung und Qualifizierung von elektrischen Isolierstoffen und Isoliersystemen" ("Evaluation and qualification of electrical insulating materials and systems") of the DKE (German Commission for Electrical, Electronic and Information Technologies) at DIN and VDE.