Surface characterization of naturally contaminated HVDC insulators

No contamination related problems were observed during seven years of service on silicone rubber insulators although a large amount of salt containing solid contamination has been deposited on their surface. The contamination layer consisted of solid particles and silicone oil. The contaminated insulators did not lose their hydrophobicity during a 72 hours clean fog test. The composition of the surface contamination layer explains the differences between the results of usual laboratory contamination tests and the good performance of silicone rubber in outdoors insulation.