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Long-term deconditioning of gas-filled surge arresters

ABSTRACT The aim of this paper is to identify parameters that influence the long-term deconditioning effect of gas-filled surge arrester (GFSA) and to provide practical recommendations for mitigating this effect. Namely, after some period of time, on order of hours or days, during which there is no activation due to overvoltage, the deconditioning of GFSA occurs. This effect was observed experimentally within the paper. The observed parameters that could influence the long-term deconditioning effect were the following: shape of voltage load, gas type, gas pressure, interelectrode distance, electrode material, electrode surface topography as well as GFSA design such as two- or three-electrode configuration. According to the results obtained, it has been shown that the occurrence of long-term deconditioning in an insulating system, insulated by a noble gas at a subpressure and with small interelectrode distances, is a phenomenon that always occurs when the insulating system is at rest for about an hour. It has been found that the type of noble gas does not influence the long-term deconditioning. Analysis of such insulating systems' parameters, with a prospect of being used as GFSAs, has demonstrated that this phenomenon is less pronounced at higher pressures (for the same value of the pressure (p) and interelectrode distance (d) product) and for electrodes with microscopically embossed surfaces. According to the results that were obtained by noble gases and their mixtures, as well as the results that were obtained by mixtures of SF6 gas with noble gasses, it can be claimed with confidence that the effect of the long-term deconditioning is an electrode effect. It has also been established that the deconditioning effect does not depend on the electrode material except in the case of electrodes made out of noble metals, which reduce the effect. Based on these results, it can be recommended that the working point of GFSAs be set (according to the DC breakdown voltage value) at a pressure that is as high as possible (with pd = const), and that the electrode active surface should have a marked microscopic topography. In addition to this, an essential conclusion for GFSA manufacturers is that long-term system deconditioning is caused by impurities and adsorbed gases that appear at electrode during the state of rest. Out of these two causes, the influence of impurities is probably the dominant one, which is proved by considerably reduced long-term deconditioning in the case of noble metal electrodes, not susceptible to corrosion. This has also been confirmed by a less distinct effect of long-term deconditioning in the case of sandblasted electrodes that have a stronger tendency towards gas adsorption and a weaker tendency towards corrosion. However, it has been shown that adding of the third electrode (that is concentric to the main electrode system) on a free floating potential along with usage of sandblasted electrodes and with smaller interelectrode distance significantly reduces the effects of the long-term deconditioning.