Contamination performance of polymeric insulating materials used for outdoor insulation applications

Results of a laboratory evaluation of the contamination performance of silicone rubber and EPDM (ethylene propylenediene monomer) rubber polymers are presented. it is shown that due to significant material differences, these polymers cannot be evaluated using experimental conditions standardized for porcelain and glass. Test conditions which yield good correlation to service experience with polymeric insulators are presented. it is demonstrated that a meaningful contamination test for polymers is a salt-fog test using water at low (250 μmS/cm) conductivity with the samples being electrically stressed at 40 V_rms/mm. Under these conditions it was possible to observe the following, which has been demonstrated by service experience: (a) the leakage current is dependent on the polymer material, (b) silicone rubber resists the continuous water film formation on the surface for a much longer time than EPDM, and (c) more degradation has been observed on EPDM than on silicon rubber