The durability and performance of polymer housed metal oxide surge arresters under impulse current stresses

Unexpectedly, many failures of modern MOA types have happened in some laboratory tests where arresters are stressed with either multipulses or series of impulse current stresses. The typical failure mode in these tests was an internal flashover over one or more metal oxide discs in an MOA. In this paper the effects of internal humidity content on the internal flashover failure tendency are reported. The polymer housed arresters tested were exposed to a humidity stress in such a way that internal humidity content in the arresters gradually increased. At the same time impulse current stress series were regularly applied to the specimens. The test results are discussed and compared to the results obtained in a similar impulse current stress series conducted earlier on arresters of the same types at Tampere University of Technology. In that test series only impulse current stresses were applied on arresters without any other stresses