LAUSR

Abstract It is well known that particles, especially conducting particles, have a detrimental effect on the dielectric strength of transformer oil. This article investigates the influence of iron particles on the breakdown voltage of transformer oil. The breakdown voltage of transformer oil contaminated with iron particles of different median diameters and quantities was measured at pulsating DC voltage. For comparison, identical experiments were performed at AC and DC voltage, respectively. The Weibull distribution was adopted to analyze the breakdown voltage data and thus the effect of particle number and particle size on the breakdown voltage of transformer oil was obtained. The experiment results showed that the breakdown voltage of transformer oil decreases with an increase of the particle number and particle size. The breakdown voltage of contaminated oil is smaller when there is DC component contained in the applied voltage, which is because of the increasing possibility of bridge formation in transformer oil with the presence of DC voltage. The limit of particle number was also calculated for transformer oil subjected to pulsating DC voltage and found to be lower than that at AC voltage, suggesting that the limit of particle number should be individually defined for converter transformer oil.