Influence of oil-paper insulation aging processes on temperature of bubble effect initiation.

The initiation temperature of bubble effect in oil-paper insulation of different ageing stages and different water contents in paper was determined. The initiation temperature of bubble effect was investigated for the new paper of polymerisation degree DP=1357 and aged paper (DP=341). Moreover the role of dielectric losses in increasing of the temperature of transformer insulation system, which leads to bubble effect was investigated. The authors also presented research results of the dielectric loss factor of oil-paper insulation, new and aged, depending on its moistening rate and temperature.