Influence of material and electric stress on the performance of polymeric insulators

On the Swedish West-coast, the behavior and stability under saline pollution conditions of polymeric silicone insulators (SI) and EPDM rubber insulators are studied. A relative comparison of leakage current data, for both AC and DC energized insulators, was made for insulators with the same leakage distance but with different polymeric material (SI and EPDM respectively), and for SI insulators exposed to different electric stress. The results show that EPDM insulators under severe salt storm conditions lose their hydrophobicity and have high leakage currents. Of the four EPDM insulators included in the test, two failed during the salt storms. Silicone insulators with the same leakage distance as those of the EPDM insulators have shown very low leakage currents. However, silicone insulators with shorter leakage distance show leakage current pulse peaks which are almost of the same magnitude to those of EPDM insulators with the longer leakage distance. The results emphasize that good long term performance of polymeric insulators in a polluted environment can be achieved if both insulator material and electric stress are properly chosen