Microarc oxidation layer on aluminum surface significantly suppresses partial discharge at triple junction point on insulation surface

Abstract

The surface discharge at metal/insulation/gas (or vacuum) triple junctions (TJs) poses a serious threat to the insulation reliability of high-voltage equipment. An insulation layer was fabricated on the surface of aluminum metal electrodes via microarc oxidation (MAO) to suppress surface discharge at the TJ. The partial discharge inception voltage was effectively increased by up to 54.5% with the MAO layer. At 1.5 kV, the average discharge magnitude per minute at the TJ decreased by up to 66.7% after MAO treatment. The composition of the insulation layer is primarily Al2O3 and Al2SiO5. As the MAO duration and voltage increase, the thickness and surface pore area ratio of the MAO layer increased continuously. The mechanism of partial discharge suppression was investigated by analyzing the layer's composition, resistivity, surface potential decay, and phase-resolved partial discharge spectrum. The analysis indicates that the mechanism primarily involves suppressing the direct or indirect movement of electrons from the metal electrode to the gas. Consequently, this suppression reduces both the number of seed charges for electron avalanches and the probability of avalanche initiation at the microscopic level. At the macro-level, the insulation layer eliminates the traditional TJ, establishing a TJ of insulation/insulation/gas (or vacuum). This work proposes a strategy for suppressing surface discharges at TJs through metal surface modification.