Introduction: It is known from experience that gas-insulated switchgear (GIS) substations are susceptible to the effects of charge trapped on isolated sections after switching. The DC electric field associated with trapped charge can lead to migration of charge onto insulator surfaces and a reduction in the withstand performance. Since the mechanism by which charge migrates onto the insulators has not been identified, it is difficult to eliminate the problem at the design stage and, at present, the effects of trapped charge are managed by adopting special switching procedures for GIS. The present work aims to understand migration of charge onto GIS insulators by applying modern measurement techniques so that the issue may be eliminated by appropriate design.

Objectives: The mechanism(s) by which charge accumulates on the surfaces of solid support insulators in GIS are to be investigated to recognise the design factors that confer immunity or susceptibility to trapped charge, to eliminate at identified sites the requirement for special switching procedures for GIS and to incorporate appropriate clauses in specifications to eliminate susceptible designs.