Electric field computation for a 400 kV composite cross-arm

If not well designed, high voltage composite insulators are prone to ageing and failure due to corona and electric field stress. Particular care is required designing areas where the metal end connections meet the insulator core, otherwise a large electric field enhancement is observed. It is difficult to completely eradicate corona on any insulator, thus manufacturers try and minimise this phenomenon by designing the assembly to increase the corona inception voltage across the end connections and other metallic components. Often this involves introduction of corona rings, especially at the high voltage end of the composite insulator, to manage the magnitude of the electric field. The use of FEA to design corona/grading rings and optimise their position has recently been of great interest. The present paper reviews the use of FEA simulation to design stress relief devices across the high voltage end of a composite insulating cross-arm. Design work has been realised in practice and verified using corona inception measurements and compared to previous FEA results.