Analysis and simulation of field distribution in micro cavities in solid insulating materials

Internal discharges in cavities in solid dielectric materials lead to the degradation, deterioration and complete failure of insulating materials. This would shorten the life time of the electrical equipments, which affects the reliability of power supply. This research is an investigation and study of the internal discharges, as magnitude and energy, in micro cavities in solid dielectric samples. The field distribution in these cavities was simulated, modeled and calculated for certain applied voltage. Alternating high voltage at power frequency at room temperature was applied with different values of the inception voltage of the sample. The cavity shape, cylindrical and spherical, and its dimensions were changed, with the cavity cross-sectional area much larger than its depth. The size of the cavity was much smaller than the sample thickness. The study was done on low density polyethylene (LDPE), polyvinyl chloride (P.V.C) and ethylene polypropylene rubber (E.P.R) because of their important industrial applications. The location of the cavity w.r.t the h.v. electrode in the dielectric sample was changed, to be in the center, adjacent to the h.v. electrode and near to the ground electrode. The number of cavities was changed from one to three either in horizontal or in vertical formation or at random in the sample. The relation permittivity of the dielectric was changed from 2 to 10. The field distribution and its enhancement within the cavity were calculated by a developed program using the boundary element technique. The field magnitude inside the cavity was significantly increased by increasing the relative permittivity of the dielectric, its magnitude was enlarged for cavities adjacent to h.v. electrode. As the number of cavities was increased the discharge magnitude and energy was increased. Multilayer samples showed very interesting results. The simulated results are in good agreement with the experimental findings. This indicates the effectiveness of the simul- ation developed method.