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

Summary

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 orientation polarization and interfacial polarization can be detected in the considered time domain. Conduction can be due to proton transport along press¬board-fibre chains and due to electron-hole conduction because of delocalized electrons in the pressboard compound lignin. If pressboard is impregnated with mineral oil, additi¬onal interfacial polarization occurs at oil-fibre interfaces. Besides proton and electron-hole conduction in the fibres, ion conduction takes place in the oil-filled capillaries.

Additional informations

Authors

Ingólfsdóttir, Pálsson, Valsdóttir, Guðmundsson, Bjarnason, Guðjónsdóttir, Bjarnadóttir, Bataineh