HVDC partial discharge and surface charging on solid insulator and charge supply source characteristics in air

Summary

In order to enhance HVDC electrical insulation performance, DC electric field distribution, charge accumulation characteristics, DC partial discharge (PD) activity and breakdown (BD) characteristics in the composite insulation system with and without a solid insulator in air, were investigated. First, it was clarified that BD with a solid insulator in air shows very complicated behavior depending on DC voltage polarity and is affected not only by DC-PD activities from the high voltage electrodes but also by accumulated charges on solid insulators. BD voltages of positive DC polarity are higher than those of negative polarity. This is due to the difference in the charge supply sources and the dynamic DC-PD mechanisms depending on the polarity of the applied DC voltage. Next, by using a sphere electrode with rough and mirror finished surface with a solid insulator, the charge accumulation process of surface charging was investigated. At both polarities, the mirror finished electrode did not show the accumulation of DC charges until just before BD, while DC charges at negative polarity increased under the rough finished electrode. By FEM analysis of electric field distributions, it was found that this difference was mainly due to the electron field emissions from the cathode, easily leading to PD inception and extension. Finally, we calculated DC charge distribution accumulated on a solid insulator surface and could estimate the BDV characteristics with solid insulator configurations in air.

Additional informations

Keywords

HVDC, PD, FO, Charge, Solid insulator