Heysham 400kV substation overcoat of current transfromers on SGT2 circuit.

The current transformers had been coated with RTV Silicone HVIC approximately 12 years ago. This coating has provided the reliable maintenance-free solution expected by National Grid and the insulators have remained in continued service for this period with no flashovers.

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The insulators were accessed via Genie 45 MEWP’s. All surfaces were cleaned with a solution of alcohol (IPA) and clean water to remove contamination and provide a good key for the new coating.

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After cleaning, the existing coating was thoroughly inspected for signs of damage and to assess adhesion to the porcelain surface. Any areas of damage or poor adhesion were removed from the insulator and the exposed porcelain cleaned with IPA. Once prepared, the ‘exposed’ areas were coated to build up to the level of the surrounding coating. Then all surfaces of the insulators were completely overcoated with fresh silicone.

Picture 7 above shows the hydrophobic affect of the coating during rainfall. This is the first form of defence against flashover. The discrete water droplets prevent electrical tracking across the surface and hence disrupt the mechanism to flashover.