Performance of Non-ceramic Insulators in Tropical Environments

Doktorsavhandling, 1999

Non-ceramic insulators have been tested in the field and under laboratory conditions in many countries for more than three decades. Nevertheless, information about their performance in tropical environments is rather limited. Thus, this project was conducted in order to fill the gap. Six different types of 33 kV insulators (silicone rubber, EPDM, RTV coated porcelain and porcelain) were installed at three different sites exposed to marine, industrial and clean environments in Sri Lanka. The insulator performance was periodically tested by visual scrutiny, hydrophobicity classification and pollution severity measurements for more than three and half years. The silicone rubber insulators and RTV coatings, in general, preserved hydrophobicity, whereas the EPDM insulators showed distinct surface changes. Porcelain insulators flashed over on several occasions. Algae growths were found on silicone rubber surfaces but, their effects on insulator performance were not strong. In parallel, laboratory tests were carried out on insulators in order to develop a method of evaluating insulator performance. A leakage current data acquisition system was developed first. Leakage current waveforms were measured on naturally and artificially contaminated insulators and the measurements were extended to artificially contaminated material samples. A non-linear behavior of leakage current was observed. It was found that this non-linearity was caused by the formation of dry band on hydrophilic surfaces in the presence of contamination. It's relation to surface hydrophobicity and electric stress has been described. Non-linear leakage currents were modeled by RC components characterizing a polluted surface. Neural networks were trained to recognize different leakage current waveforms. It has been suggested that the trained neural networks could be used, in practice, for estimating the risk for flashover development.