Leakage current monitoring and outdoor degradation of silicone rubber

The degradation process of silicone rubber was investigated by leakage current monitoring in the inclined-plane method. A data acquisition system (DAS) with 12-bit, 8-channel analog/ digital (AD) converter was prepared. The maximum erosion depth was measured for use as the degradation indicator. The result suggests that the discharge duration and current waveform are well corresponding with the degradation process. And fast Fourier transform (FFT) analysis from the stored waveform shows that the harmonic ratio I3/I1 corresponds with the initial surface transition from hydrophobic to hydrophilic, and with further progressive degradation. In addition, it may be possible to use cumulative charge and peak pulses as quantitative indicators of failure. Furthermore, the contact angle was adopted for assessing surface degradation. These results indicate that the surfaces are divided into top and bottom areas depending on the degree of exposure to dry band arcing. It seems that the bottom area subjected to most of the dry band arcing contains very short chains of silicone rubber as well as alumina trihydrate fillers, while the top area shows the loss of filler particles.