Fundamental Study on Self-healing Insulation Performance of Silicone Rubber Affected by Local Breakdown

Abstract

Feasibility of self-healing insulation system was studied. A silicone rubber without filler was mounted on a glass substrate with a needle electrode. An ac voltage with 4 kV in rms was applied. The voltage was cut off when the tree had propagated into 150 micrometers in length. After the cut-off, the partial discharge inception voltage was periodically observed. The partial discharge inception voltage had once reduced into as low as 2 kV. However, it gradually increased with time, and finally exceeded the tree inception voltage (4 kV) when 30 - 60 hours had passed. It was also observed by optical microscope that the tree gradually disappeared in parallel with the recovery of the partial discharge inception voltage. The same phenomenon was observed even if 1 kV ac voltage had been continuously applied during the process of the recovery. A simulation using a needle-shaped void was performed in order to clarify the mechanism of the self-healing effect. It was observed that the tip of the needle-shaped void gradually got wet with a liquid material. It would be the result of "bleed-out" of the low molecular component included in the rubber. The tip of the void was finally filled with the liquid, however, the rest of the needle-shaped void stayed without being filled. In this type of tree, it was suggested that the self-healing effect is expected if the diameter of the tree did not exceed ca. 5 micrometers.