Reasons for Corrosion and Exfoliation of Silver Coating on Bushing Wiring Board of HGIS in a Coastal Substation

The silver coating on one side of bushing wiring board of 66kV hybrid gas insulated switchgear (HGIS) in a coastal substation corroded and exfoliated in a large area. The failure reasons of the silver coating were studied by means of macroscopic morphology observation, chemical composition analysis, metallographic examination and scanning electron microscopy, combined with atmospheric environment data in service area. The results indicated that the blistered and exfoliated silver coating was oxidized or vulcanized, and the exposed substrate was also oxidized. The corrosive mediators entered the interface between the aluminum alloy substrate and silver coating through the pits, scratches or interfacial gaps on the surface of silver coating, which was the main reason for the corrosion and exfoliation of the silver coating on the wiring board.