Partial discharged-induced aging of cast epoxies and related nonstationary behavior of the discharge statistics

Physics and chemistry of partial discharge and corona - recent advances and future challenges

“…Nonstationary behavior of PD has been observed under a variety of experimental conditions [18,19,26,27,651. By the term nonstationary behavior it is meant that the statistical characteristics of PD such as the pulse-height or phase distributions have a dependence on time.…”

“…Additional evidence of the effect of changing surface conductivity is provided from recent work on point-epoxy gaps [18,27, 681. Figure 9 shows examples of integrated charge distributions, po(Q+) and po(Q-), measured at different indicated times for discharge pulses generated by applying a 50-Hz, 3.0-kV rms alternating voltage to a sharp point electrode that touches a flat cast epoxy surface.…”

“…Included in these investigations are measurements of: (1) gaseous by-products from the discharge [15, 161, (2) removal of solid material or other local changes in morphology [17], (3) changes in solid dielectric surface resistivity [18, 191, (4) surface acidification, oxidation or deposition of material [20, 21, 221 and (5) growth of voids, cracks, or trees within a dielectric [23, 24, 25, 261. It has been noted [18,27] that the PD-induced changes in the discharge site characteristics will in turn cause changes in the PD behavior that make the phenomenon inherently nonstationary. The susceptibility to nonstationary behavior complicates the interpretation of PD signals.…”