The influence of water content and ageing degree of paper insulation on its mechanical strength

The article concerns the issue of mechanical strength of paper insulation in dependence of its ageing degree and water content. The authors focused on tearing resistance of Kraft paper. The tearing resistance of paper was determined using Elmendorf method. The ageing level of the paper samples was described by means of cellulose polymerization degree. The water content in paper samples was determined using Karl Fischer titration method. The investigations were conducted for various combinations of water content in the range from 7.24% to 0.12% and polymerization degree in the range from 1360 to 272. The results proved significant influence of water content in paper insulation on its mechanical strength. The drying of cellulose insulation causes significant weakness of mechanical strength of paper. This conclusion is particularly important in aspect of drying of aged transformer.