Swansea North Circuits 1 and 3 are at National Grid’s Pembroke 400kV substation. This substation is coastal and near a large oil refinery. Furthermore, dust is being created by the construction of a new gas fired power station directly opposite the substation. Therefore the main pollutants that could potentially cause flashover at this site are salt, petrochemical and construction dust.

The through wall bushings, VT’s and support posts had been previously coated in WT235 grease which had become saturated with pollution and no longer providing protection. The other insulators were uncoated.  

A polluted surface causes the insulator to become hydrophilic which results in wetting during high levels of moisture or rainfall. This could cause arcing and tracking on the surface which would ultimately lead to flashover.

Access to the insulators was by Mobile Elevated Work Platforms.

As usual the grease  had become hardened to porcelain surfaces of the insulators and was difficult to remove. All surfaces of the insulators were thoroughly cleaned and absolutely all traces of hydrocarbon grease removed.

Finally the insulators were coated with RTV Silicone HVIC to a thickness of approximately 0.5mm. This will provide maintenance-free protection for an expected minimum of 10 years in this highly polluted environment. In 10 or more years time the insulators can be re-coated with rtv silicone. Surface contamination does not stick to the silicone surface so cleaning is relatively simple and a lot less time consuming!