Thermal aging micro-scale analysis of power transformer pressboard

Abstract

In order to analyze the thermal aging mechanism of the insulation paper inside the power transformer, a series of accelerated thermal aging tests were performed on pressboard. Subsequently, the atomic force microscope (AFM) together with scanning electron microscope (SEM) and X-ray diffraction (X-RD) were utilized to observe the micro surface of the thermal-aged pressboard. The experiments and analysis indicate that either the links among the D-glucopyranose units or the hexagonal mesh structures of the D-glucopyranose units were broken under thermal stress; the number of D-glucopyranose units after 6 weeks of aging was 0.8-1 per nm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , only about one third of un-aged value. The wall of a cellulose cell was deteriorated and thinned by thermal stress. At the same time, the cracks expanded gradually on the surface of the cellulose, which shortened the average width of cellulose fiber from about 40 mu of un-aged sample to about 25 mu after 6 weeks of aging. Meanwhile, the relative crystallinity and the size of the crystallite in the pressboard decreased nonlinearly with the thermal aging time.