Influence of the electrodes coating with thin layers on the dielectric strength of transformer oils

This work is aimed at the influence of electrodes coating with thin layers of polytetrafluoroethylene (Teflon) on the dielectric strength of transformer oils. It's shown that such a deposit on the electrodes enables one to improve significantly the dielectric strength, under AC voltage, of fresh mineral oil as well as oils containing products of decomposition resulting from electrical discharges. The influence of coating is all important as the radius of the sphere electrode is small. On the other hand, in presence of particles (impurities), the electrode coating enables to reduce the local electric field in the vicinity of particle and hence to avoid micro-discharges which can be initiated between the metallic electrodes and these particles