Internal degradation of polymer housed metal oxide surge arresters in very humid ambient conditions

A total of 19 new, polymer housed metal oxide surge arresters of seven different types were tested in a 25-month moisture ingress test series in very humid ambient conditions at Tampere University of Technology (TUT). Internal degradation due to moisture ingress in the different arrester types during the test with respect to the internal structure of arresters is reported. Only three of the seven arrester types tested showed good performance throughout the test. These arrester types had a housing molded directly on the arrester body. Most of the other arresters failed during the test or immediately after the test under an AC voltage stress. The trend of the internal leakage current was found to be heavily dependent on the internal structure of an arrester