In order to protect other power equipment from dangerous overvoltages, the arresters themselves are employed in the most exposed locations. Hence, under extreme adverse conditions they may be overstressed.
Surge arrester housings have traditionally been made of porcelain. However, today there is a strong trend, and often even a preference, towards the use of silicone insulators for arresters at all system voltages. There are a number of reasons why silicone is seen as an attractive alternative to porcelain, including potentially better short-circuit capability with increased safety for other equipment and personnel if correctly designed.
It is false, however, to believe that safer short-circuit performance is automatically achieved simply by replacing the porcelain housing with one made of polymer. In the past, there has been the incorrect belief that all polymer-housed arresters, irrespective of design, were capable of carrying enormous short-circuit currents. This is not the case, and the design must be scrutinized carefully for each specific type. Please read the enclosed article (links section, right hand side) where you will see how ABB's patented safety belt winding results in an excelllent short-circuit performance.