Surface ageing mechanisms and their relationship to service performance of silicone rubber insulation

This paper identifies corona and local arcing as the major ageing influences on silicone rubber surfaces. The hydrophobic properties of silicone rubber lead to the formation of discrete water droplets on the surface and these can lead to local enhancement of the electric field and corona activity. This activity leads to surface ageing and a consequent loss of hydrophobicity. Once wetting takes place, surface currents flow and dry bands form. Arcing across dry bands also leads to ageing but this is not as deleterious as corona ageing. Experimental evidence on corona ageing and the stages in the ageing process, in service, are presented.