Thermal ageing of cellulose paper insulation

Results are presented of investigations into the thermal ageing behaviour of cellulose paper insulation in which tests at temperatures of between 100 °C and 160 °C have been carried out on well-dried samples of cellulose paper contained in sealed glass vessels in an atmosphere of initially dry nitrogen gas. The degree of ageing has been assessed by measuring the time rate of decrease of several physical and physico-chemical characteristics of the cellulose paper, e.g. burst strength, degree of polymerisation etc., and conclusions drawn concerning their relative sensitivities to the state of ageing of the test sample. In addition to these measurements the rates of production of the main gaseous decomposition products have also been determined. This work is preliminary to a more extensive investigation into the effects of ageing, both thermal and electrical, on the life of oil-filled cable insulation and the present results are discussed in this context.