Diagnostic methods in revealing internal moisture in polymer housed metal oxide surge arresters

Diagnostic measurements performed for surge arresters are normally studied by evaluating their suitability to detect aging and degradation of metal oxide material. The suitability of different methods for revealing internal moisture in arresters has not been studied much. This aspect is considered in the paper based on measurement results obtained during a 1.5-yr laboratory test series conducted for six different types of polymer-housed distribution class arresters. AC power losses, third-harmonic content of resistive leakage current, dc leakage current, and partial discharge measurement results over the test period are given and discussed. Details of the measurement procedures suitable for measuring polymeric arresters with internal moisture are also studied. AC power loss and dc leakage current measurements were found to be good methods, whereas the other two can only be used as additional methods when diagnosing internal moisture in polymer-housed arresters.