Chapter 6 - Insulators

Abstract

This chapter describes the different types of overhead line and substation insulators, their design characteristics, and their application. Conductors are attached to their support by means of an insulator unit. For overhead lines up to 33 kV and for outdoor substation equipment, the insulator is typically of the post- insulator type. For overhead lines above 33 kV and substation aerial conductor busbars, suspension, or tension cap, and pin or long rod insulator units are employed. Insulators must be capable of supporting the conductor under the most onerous loading conditions. In addition, voltage flashover must be prevented under the worst weather and pollution situations with leakage, currents kept to negligible proportions. There are three basic insulin materials available: polymeric composite, glass, and porcelain types. Overhead line polymeric insulators (sometimes called “silicone insulators”) are a development dating from the 1960s. They have the advantage of reduced weight, high creepage offset, and resistance to the effects of vandalism since the sheds do not shatter on impact. Epoxy resin cast insulators are extensively used in indoor substation equipment up to 66 kV and metal enclosed switchgear. Epoxy resins have been used to a limited extent on medium voltage current transformers installed outdoors and in particular on neutral connections, where the insulation is not subject to the same dielectric stress as the phase conductor supports.