Consideration into CIGRE round robin contamination test of polymer insulators

Hydrophobic polymer insulators show higher contamination flashover voltages compared with ceramic insulators, but standard artificial contamination test methods have not yet been established. Test methods used for ceramic insulators are now usually used also for polymer insulators, but due to different surface properties and configurations between ceramic and polymer insulators, test procedures and conditions for ceramic insulators may not be pertinent for assessing polymer insulators. Under such circumstances, CIGRE WG C4.303 started round robin tests and results from four laboratories were presented but some differences were obtained. In order to clarify the factors for such differences, effects of ambient temperature, artificial fog injection rate into test chamber and kind of non-soluble contaminants were investigated. Any significant effect of ambient temperature on contamination flashover voltage was not found, but discernible effect of fog injection rate was found on the flashover voltage of longer time rested insulators. In addition, about 10% difference in flashover voltage was found between Kaolin and Tonoko both under the no rest time and the longer rest time conditions.