Aging Study of Oil Impregnated Repulped and Standard Cellulose through Measuring Viscometric Degree of Polymerization

This paper describes the aging behavior of the oil impregnated repulped cellulose and compares it with the aging behavior of the oil impregnated standard cellulose. In order to evaluate the reliability of using repulped cellulose in transformers, the accelerated aging process was applied to both types of cellulose by increasing the temperature to 150 °C and their aging behavior was studied and compared through measuring their viscometric degree of polymerization (DP) in consecutive aging periods. Results were fitted to estimate an aging relation respect to the initial DP and this was yield that the accelerated pyrolysis behavior of two survived types of cellulose are completely similar and obeys the same damping model. From the obtained results, it can be concluded that the moulded insulating parts made of repulped cellulose can be used in the insulation system of power transformers with a good and acceptable reliability. The reduction of DP to 30% of its initial value was estimated as a criterion for the end of life time of these celluloses.