Metallic particle effect on the AC breakdown strengths of vegetable insulating oil

The vegetable insulating oil is applied increasingly as dielectric liquid in transformers, but it is vulnerable to particles especially the metallic particles. In this paper, focus is made on the influence of metallic particles such as copper and iron particles on the breakdown strengths of vegetable insulating oil. The relationship of AC breakdown strengths and the metallic particle concentration as well as its difference between mineral insulating oil and vegetable insulating oil were obtained and analyzed. Experimental results indicate that the AC breakdown strengths of vegetable insulating oil are higher when it is not contaminated with metallic particles, and decrease slower with the increase of metallic particle concentration than those of mineral insulating oil. The influence of copper particles on the AC breakdown strengths of the two insulating oils is greater than that of iron particles. Since the breakdown strengths of vegetable insulating oil with higher viscosities are less sensitive to the metallic particles, it has a better insulating performance under AC stresses with the existence of metallic particles.