The key role of surface conductivity in the early ageing period of epoxy based insulators

Presents experimental diagnostic tools to correlate surface electrical property evolution to surface chemical modifications during ageing. The authors demonstrated that the surface conduction increase during UV irradiation was due to the transformation of the initial ethers and esters in acids and alcohol photo-oxidation products which are 10 times more hydrophilic. It is the hydrophilic power that is responsible for the high sensitivity to the relative humidity.