Capacitance change during the aging of a combined system of a solid-liquid dielectric under switching impulse voltages

This paper presents the result of an experimental investigation of the arising non-linear phenomena in bakelite and phenol impregnated pressboard specimens (pertinax), immersed in insulating oil, under the application of high voltage impulses. For this purpose, bakelite and pertinax samples were electrically stressed with 250/2500 μs switching impulse voltages through a tip-plane electrode assembly. The total electric charge flow through the specimens and the overall capacitance C of the metal tip-solid dielectric-metal plane combination were measured in the high-field regime, the experimental results show an exponential increase of the overall capacitance which may be attributed to the excessive charge flow due to the electron avalanche effect. The aforementioned capacitance involved with the partial discharges depends on the environment temperature (partial discharges enhanced by temperature). Further theoretical consideration leads to a mathematical model which gives an expression for C. The theoretical expectations on the basis of this model are found to be in good agreement with the obtained experimental results