18 - Surge Arresters: Application and Selection

Abstract

This chapter discusses the selection and applications off surge arresters. Arresters or diverters are generally of two types: gapped or conventional and gapless or metal oxide; and the choice between them depend on the power frequency system voltage, characteristics of the voltage surges and the grounding system. The purpose of a surge arrester is to safeguard a system against probable transient conditions; particularly those that may exceed the safe impulse withstand level of the equipment. To provide the required level of surge protection for equipment or a power system against possible transient frequency voltage surges, ZnO gapless surge arresters are the latest in the field of insulation coordination. The basic parameters that should be considered while selecting a gapless surge arrester are service conditions, mechanical soundness, maximum continuous operating voltage, basic insulation level, and the arrester's nominal discharge current. Surge arresters are employed for installations and equipment that are not so critical as to cause a shutdown of the power system. Likely applications include small distribution networks and equipment – such as a distribution transformer, feeding residential or small industrial loads – are not directly exposed to the atmosphere and hence, to direct lightning strikes. Such installations are reasonably shielded, as when installed within a city.