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, SF
6 gas and a metal electrode come in contact.
Using four kinds of test samples, we have measured the flashover voltages V
f. The voltages V
f become lower than the theoretical voltages V
s 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 V
c from the voltages V
f, and investigated the relationship between the voltages V
c and the theoretical values V
s. The values of V
s/V
c, which characterize the properties of the partial discharges, can be shown by the product λ S
90%E
avP of the following parameters; (1) coefficient λ representing the surface roughness of electrode at the triple junction, (2) effective area S
90% of the electrode, (3) average field E
av at the area S
90%, 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 V
s/V
c.
View full abstract