Dielectric Behavior of HVDC Insulating Materials, Polarization and Conduction Processes in Mineral Oil and in Pressboard Impregnated with Different Fluids

The dielectric behaviour of insulation materials is a key factor for the reliable operation of HVDC equipment. Materials considered here are mineral oil and pressboard. For a deeper understanding, pressboard is examined both with gas impregnation and with mineral oil impregnation. Both cases exhibit different dielectric behaviour. The under-standing of polarization and conduction are of great importance, because field distributions in HVDC equipment depend on these processes and mechanisms. It is found for mineral oil that there is no polarization, and conduction is due to drifting ions. These ions mainly remain as heterocharges at the electrodes and are almost not neutralized. After polarity reversal, they are available as homocharges for further transport processes. In pressboard, only…