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Static electrification as an evaluation method of thermal aging in transformer oil

The experimental results of static electrification of several kinds of thermally aged transformer oil are presented in this paper. A pure oil sample and four oil samples in presence of copper, pressboard, silicon steel sheet, copper+pressboard+silicon steel sheet respectively, have been aged at 110/spl deg/C under air condition. Static electrification measurement at different aged degree was carried out in a system with the sintered metal filter. The changes of static electrification are compared to classical aging indexes, such as loss factor (tan /spl delta/), conductivity (/spl gamma/) and acid number (AN). The experimental results show that static electrification has relationship with thermal aging and the sensitivity of classical indexes for thermal aging process is smaller than changes of static electrification.