Influence of metallic particles on the breakdown voltage of insulating oil at AC and DC voltage

摘要

The insulating performance of transformer oil is vulnerable to metallic particles, especially oil used in HVDC converter transformers. The electric field distribution in converter transformer insulating oil is different from that in traditional AC transformer insulating oil, so extra attention should be paid to the influence of metallic particles on its breakdown voltage. This paper investigated the influence of metallic particles on the breakdown voltage of insulating oil at AC and DC voltage. The breakdown voltages of insulating oll contaminated with iron particles and copper particles of different sizes and particle numbers were measured at AC and DC voltage, respectively. The Weibull distribution was adopted to characterize the breakdown voltage data and the relationship between the breakdown voltage and particle numbers was obtained. The effect of particle diameter was also investigated. The experiment results showed that the breakdown voltage of the insulating oil decreases with the increase of the particle number. More importantly, the breakdown voltage at DC voltage is smaller than that at AC voltage and the insulating oil contaminated with iron particles of bigger median diameter has a smaller breakdown voltage.