Abstract
Metal oxide varistors are applied today inside modern surge arresters for overvoltage protection for all voltage levels. Their main issue is the thermal activation of their crossing current, which could lead to complete destruction by thermal runaway. This article presents a new technological solution developed in order to increase the thermal stability of metal oxide varistors. It consists in connecting in parallel two or more similar varistors (for dividing their current), having a thermal coupling between them (for equalizing their temperatures and forcing them to act together and simultaneously as much as possible). Starting from a finite element computer model performed for each situation (varistor standalone or parallel), up to real measurements, the thermal stability of the equipment was analyzed in permanent and impulse regime. Experiments were carried out in the same conditions. Experimental data obtain from two disk varistors corresponds very well to simulations, proving that parallel connection of varistors, combined with a thermal exchange between them is an efficient technical solution for thermal stability improvement, even if not apparently economically justified.
Highlights
Metal Oxide Varistors (MOVs) are the newest and most advanced category of surge protectors due to their obvious advantages
Parallel connection of varistors may be a technical solution worth taking into account only under certain conditions
The parallel connection of the varistors does not bring any improvement in their operation
Summary
Metal Oxide Varistors (MOVs) are the newest and most advanced category of surge protectors due to their obvious advantages. MOVs are manufactured in an extremely wide range, as protective equipment for each voltage level, from telecommunication networks and low voltage electrical installations to high and very high voltage, regardless of the current type (AC or DC). The research on non-linear properties of semiconductor ceramics based on metal oxide mixtures dates back to the 1950s and was carried out in Japan and the former Soviet Union, the first patent in this field, owned by the Japanese company Matsushita Electric Industrial Co., was granted in. In low-voltage and telecommunications, small and medium-sized companies are predominant, equipment in this area not being highly demanding as manufacturing technology. We will not detail the existing technical solutions along the way [3]
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