Aspects of the performance of metal oxide surge arresters in different environmental conditions

Metal oxide surge arresters (MOAs) have been in use for only a rather short time. Some means are needed for predicting how various stresses affect the operating parameters and the possible failure of MOAs. In contrast to conventional arresters, the varistor elements of MOA are subject to considerable voltage stress, and a small leakage current continuously passes through an MOA giving rise to new phenomena unknown in arresters with gaps. To be able to predict the operational stability and the potential failures of arresters, much data is needed on the effects of environmental stresses. Such data can be gathered both in controlled condition tests, i.e. laboratory tests, and in long-term field tests in different environments. In addition, the field experiences of the users of arresters are of great value. Much benefit could be obtained if data pertaining to the operational stability and potential weaknesses of arresters could be collected at a moderate cost in a reasonably short time, say in a few days or at most a few weeks. If such short term procedures were available, different types of arresters could be subjected to a set of tests involving different stresses and combinations of stresses. This paper presents some results of a research project conducted at the High Voltage Laboratory of Tampere University of Technology (TUT) during the years 1994-6. The main results of the cold tests, the water immersion tests and the impulse current stress series are presented. In addition, one failure mechanism discovered for porcelain covered arresters with internal air space is presented