Influence of Silicone Oil and Gold Coating during the Space Charge Measurements on Epoxy Resin Specimens

Epoxy resin has been widely used in dry-type insulation application, such as dry-bushings. This paper focuses on the silicone oil effect on the space charge characteristics of epoxy resin in PEA system. The measurement results on samples coated with gold showed that almost no charges were injected under such a short polarization time at 30°C. However, the measurement results on uncoated samples showed that homo charges were injected very quickly into the samples. Silicone oil was undertaking voltage and charges were injected firstly into the oil and migrated into the measured specimen, which significantly reduces the threshold electric field strength for charge injection. Interlayer polarization occurred at the interface (oil-specimens) and the interface charge dissipated along with poling time. So the charge peak near the cathode decreased and the image charge also dissipated. Therefore, for samples that are hard and not flat, like epoxy resin, gold coating is very important to obtain an accurate result of charge dynamics.