AGING OF TRANSFORMER INSULATION PAPER

As a transformer ages, the chemical and physical properties of the cel lulose insulation materials in the transformer change, and the paper l oses its strength and becomes brittle. The average molecular weight of the cellulose chains decrease with age, and degradation products are formed, including water, carbon monoxide, carbon dioxide, and furans. The molecular weight changes in the cellulose have been studied by sev eral methods, but the GPC method for determination of the molecular we ight has been shown to offer advantages over other methods because it yields the total molecular weight distribution. The tensile strength o f the cellulose insulation in transformers also changes with age as a result of the changing molecular weight of the cellulose. Work carried out in our laboratory on the aging of cellulose insulation is reviewe d in this paper. Our studies have included investigations of insulatio n materials from retired transformers as well as accelerated aging of insulation paper in transformer oil in the temperature range of 129-16 6 degrees C under vacuum. In the study the relationships between the m olecular weight of the cellulose and the furan degradation products an d tensile strength have been delineated, and they have been correlated with information on the kinetics of degradation of the insulation pap er.