抄録
In the present report the authors propose the method to estimate the minimum breakdown voltages of surface flashovers initiated from the triple junction at which a solid insulator, SF6 gas and a metal electrode come in contact.
Using four kinds of test samples, we have measured the flashover voltages Vf. The voltages Vf become lower than the theoretical voltages Vs of streamer inception in the case of the test sample with the large electrode area at the triple junction. To understand the phenomena quantitatively, we estimated the real partial discharge voltages Vc from the voltages Vf, and investigated the relationship between the voltages Vc and the theoretical values Vs. The values of Vs/Vc, which characterize the properties of the partial discharges, can be shown by the product λ S90%EavP of the following parameters; (1) coefficient λ representing the surface roughness of electrode at the triple junction, (2) effective area S90% of the electrode, (3) average field Eav at the area S90%, and (4) gas pressure P. The minimum surface flashover voltages in the insulators for coaxial electrode systems can be estimated precisely, considering the properties of Vs/Vc.
