Influence of electrodes coating on the initiation and development of electroconvection in transformer oils

This work reports on the influence of electrodes coating with thin layers of different materials, on the initiation and development of the electroconvection. The investigations are achieved with a sphere-plane electrode system of aluminum. The considered oil samples are fresh and aged ones. The thin layers are deposits of polytetrafluoroethylene, silicon oxide and silicon nitride, obtained by magnetron sputtering. It shown that the nature of coating materials as well as the geometry and polarity of the electrodes greatly influence the threshold electroconvection voltage (i.e., the voltage required to set the liquid in motion). The effect is more marked when both electrodes are coated; the influence of polarity is more significant with fresh oils than with aged ones. At high voltages, the liquid motion is slower and the laminar character of streaming persists within a wide interval of voltages than in the case of uncoated electrodes.