Insulators for 1000 to 1500 kv Systems

In areas of heavy pollution, the risk of flashover at working voltage as a result of conducting layers on the surface is likely to be the limiting criterion for insulator length. Performance is being evaluated in natural pollution to determine whether or not values used at lower voltages may be linearly extrapolated to 1000 to 1500 kV. To carry the large conductor bundles, insulators will need a heavy mechanical rating. Very strong resin insulators with fibre-glass cores can be produced. Such insulators can have greater leakage path in a given length than conventional porcelain or glass, and hence give a reduced overall length. Another method of reducing length is to use a porcelain with a resistive glaze; this improves performance in pollution both by drying the surface and suppressing discharges. In substations and on lines, assemblies of individual post and string insulators will be used to give improved mechanical characteristics and reduce the height of substation structures and line towers for reasons of amenity and cost.