Copper influence on the ultraviolet visible spectroscopy and property of oil in the ageing process of oil-paper insulation

The insulation paper wrapped copper winding is immersed in insulation oil to provide insulation in power transformer. The copper corrosion/dissolution in oil-paper insulation system has been attracted great attention. However, not enough data have been obtained about the copper products influence on physicochemical and electrical properties of oil in the process of oil-paper insulation ageing. In this paper, the thermal ageing experiment of four combinations of oil-paper insulation samples which were consisted of Karamay 25# naphthenic oil, Karamay 25# paraffinic oil, Kraft paper wrapped with and without copper strip at 110°C and 130°C was conducted. The oil acidity, viscosity, breakdown voltage and ultraviolet-visible (UV) spectroscopy of the insulation oils with different ageing condition were analyzed. Results show that the oil acidity increases with oil ageing. The viscosity and breakdown voltage of different oils shows fluctuation in the ageing process. The oil aged with copper has higher oil acidity than that without copper, especially in the later period of ageing. The oils aged with copper have higher UV absorption peak values. The relationship between oil acidity and the UV absorption peak for oils aged with copper is different from that aged without copper.