The discharge along hydrophobic and hydrophilic surfaces

HV outdoor insulating systems such as line and station insulators, surge arresters and bushings, using silicone rubbers for external insulation have become very popular. Presently there are two forms of silicone rubbers that are widely used for outdoor HV insulation, namely, high temperature vulcanizing (HTV), used mainly as weather-sheds, and room temperature vulcanizing (RTV), used as a protective coating on a ceramic surface. The driving motivation for their increased use is the unique characteristic of hydrophobicity, which provides a high surface resistance, even in the presence of moisture and contamination, thereby suppressing the leakage current to low values. In this paper, the discharge phenomena along hydrophobic (with RTV coating) and hydrophilic (without RTV coating) surfaces observed with high-speed camera were studied. It is found that there was a clearly difference of discharge activity between along hydrophobic and hydrophilic surfaces. The difference of discharge is explained by means of analyzing the waveforms of the leakage current and flashover voltage.