Stochastic model of breakdown initiation in dielectric liquids

An electric strength of perfluorodibutyl ether and transformer oil in small gaps between the hemispherical electrodes was investigated experimentally under AC voltage of linearly increasing amplitude. The macroscopic stochastic approach was proposed that describes breakdown initiation by certain function mu(E). This function is the probability density of streamer inception on a small element of electrode area in a short interval of time and depends on local electric field. This macroscopic approach allows one to obtain the analytical expressions for breakdown initiation probability on various parameters of experiment for flat, cylindrical and hemispherical electrodes under constant DC test-voltage, DC and AC ramp test-voltages. Several methods were developed to reconstruct the function mu(E) using experimental data on series of breakdown voltages for case of breakdowns in small gaps between electrodes. The values of function mu(E) for transformer oil and perfluorodibutyl ether were determined in the range of electric field from 0.3 to 0.9 MV cm(-1). It was shown that perfluorodibutyl ether is a prospective dielectric liquid, especially for use in environmentally appropriate technologies. Stochastic computer simulations of breakdown inception were carried out. The series of breakdown voltages and pitting on surface of hemispherical electrode were obtained using stochastic model.