Possibilities to reveal internal moisture in polymeric metal oxide surge arresters by means of PD and EMR measurements

This paper describes the results of a test series where six different types of gapless, polymer housed metal oxide surge arresters were subjected to humidity and impulse current stresses for ca. 1.5 years. The results of partial discharge and electromagnetic radiation measurements are given in the paper together with the results of internal leakage current measurements providing an indication of the moisture content inside the arresters tested. PD activity was measured in most of the specimens of arrester types with tight interfaces between the polymeric housing and inner parts of an arrester. Arresters with considerable internal gas spaces showed no PD activity during the test despite internal moisture content. Characteristics of the PD type measured in arresters are presented. In all the cases with PD activity the moisture problem was noticed earlier from the internal leakage current measurements.