Gel permeation chromatography of the thermal degradation of cellulose insulation paper in an aged power transformer

The lifetime of a power transformer and its capacity to be refurbished is often determined by the condition of the cellulose insulation materials used to wrap the copper windings. As a transformer ages the molecular weight of the cellulose in the insulation paper decreases. Here we describe a study of the accelerated ageing of cellulose insulation paper and cotton linter under vacuum at 166°C. The study indicates that the degradation results in a bimodal distribution in molecular weight of the cellulose, which indicates that the scission of bonds in the cellulose chains is non-random, and bonds near the middle of the chains have a higher probability of bond scission than those near the ends. This has been associated with the rod-like structure of the cellulose molecules