PETRU BUDRUGEAC, IOSIF LINGVAY, ALEXANDRA PICA, BEATRICE GABRIELA SBARCEA STUDY REGARDING THE BAHAVIOUR OF AN INSULATING VEGETABLE OIL EXPOSED TO ACCELERATED THERMAL AGING The simultaneous thermal analysis method (thermogravimetry/derivative thermogravimetry + differential thermal analysis (TG/DTG+DTA) and determination of iodine index have been used for characterization of an experimental vegetable insulating oil exposed to thermal cyclic and isothermal accelerated aging in pure state and in contact with red copper. The results obtained by thermal analyses show that three main successive processes of thermo-oxidation occur at progressive heating of initial (un-aged) and thermal aged oil samples. The accelerated thermal aging determines the change of composition and thermal properties of oil, which involves the formation of sites with an oxidative reactivity greater than those from initial (un-aged) oil. It has been put in evidence the catalytic role of red copper in the process of oil oxidation. The change of composition of oil as result of thermal aging also results from the decrease of iodine index. The general mechanism of auto-oxidation of vegetable oils gives a qualitative explanation of obtained results.
Keywords: vegetable oil for electrical insulation, thermal (TG, DTG+DTA) analysis, aging, iodine index of oil, red copper catalyst