An evaluation of surface behaviour of insulating materials in presence of decomposed SF6

A testing procedure for screening candidate epoxy systems for spacers in SF₆-insulated HV (high-voltage) devices is presented, and some data on the behavior of varnished and unvarnished specimens are reported. The lack of difference in the surface resistance during and after exposures to vapors of three different HF+water solutions has been confirmed. A comparison with the behaviour of the same materials during and after attack by decomposed SF₆ gases suggests that the damage penetration depth is a parameter better correlated with the resulting material variation than the decrease in surface resistance during the exposure tests. The protective role of varnish in the HF attack was demonstrated by damage penetration depth and surface resistance measurements, complemented by optical microscope observation of morphology changes