Multifactor correlation mechanism of the deterioration degree of vegetable oil with transition metals

The iron and copper transition metal materials used in the iron core and winding of a transformer will accelerate the deterioration of vegetable insulating oil. The effect of the transition metals iron and copper on the deterioration of vegetable oils at different temperatures has not been quantitatively characterized. In this paper, multifactor analysis was used to examine the features of vegetable oil ageing. The factors in this study include the breakdown voltage, dielectric loss factor, water content in oil, acid value, and volume resistivity. Changes in time, temperature, and transition metal species were used as independent variables. First, Spearman correlation analysis showed a strong negative correlation between the acid value and the breakdown voltage, whereas a significant positive link was identified between the acid value and dielectric loss factor. Then, the breakdown voltage, acid value, and dielectric loss factor in oil under various circumstances were compared and examined based on the nonparametric test, which showed that the acid value and the dielectric loss factor in oil are clearly impacted by both changes in the temperature and the type of transition metal. Therefore, the acid value and dielectric loss were selected to characterize the deterioration performance of vegetable oil. Finally, the changes in acid value and dielectric loss factor in oil were subjected to multiple linear regression analysis. The effects of time, temperature, and transition metal species on the acid value and dielectric loss factor were linearly fitted. This study can quantify the influence of different transition metals on the ageing characteristics of vegetable insulating oil at different temperatures. This study provides a reference to further explore the quantitative characterization of the effects of transition metals and other variables on the degree of vegetable oil deterioration.