Depolymerization processes in the thermal degradation of cellulosic paper insulation in electrical transformers

A dynamic heating experiment was used to examine the influence of temperature on the degradation of the Kraft insulating paper in transformer oil. The degradation was monitored by measuring a number of key indicators on selected samples as a function of progressive ageing. These indicators included the degree of polymerization (DP), level of furanic compounds and level of gases such as carbon oxides and oxygen. The results show that the formation of furanic compounds and of gases begins significantly after a large reduction in DP, indicating a two-stage process: firstly scission leading to a sharp drop in DP and secondly formation of low molecular weight degradation products. (C) 1998 Elsevier Science Limited. All rights reserved.