Statistical texture analysis of morphological changes in pressboard insulation due to thermal aging and partial discharges

Power transformer pressboard insulation is subject to thermal aging effects during normal operation that can result in micrometer-scale physical/morphological changes to its surface. Such surface irregularities can increase the likelihood of particle/contaminant attachment to pressboard surfaces or static electrification of oil flowing along these surfaces. Both phenomena can lead to partial discharges which can ultimately lead to insulation failure. In this work, pressboard samples were thermally stressed in air inside an oven to produce pressboards with differing levels of thermal aging and therefore varying surface irregularities. Another set of samples were immersed in insulating oil after thermal stressing, and stressed electrically to produce surface tracking partial discharges. A statistical texture analysis of the thermally and electrically stressed samples was used to demonstrate that the surface condition of pressboard samples were affected by thermal deterioration and the presence of partial discharges.