Conf Presentation – Session 1.Paper 5 1

Abstract—Flow electrification phenomenon is suspected to be responsible for some failures in high power transformers. Acoustic sensor surveys from suspected transformers and visual observations in damaged transformers revealed some evidences of electrical discharges (electric "tree " paths, "worm holes", presence of carbon...) on inner pressboards. Nevertheless the scenario, which lays the electrostatic activity and consequently transformer failure, is still not well understood. The goal of this work is to propose some elements for understanding electrostatic hazards in high power transformers. Experimental set up has been developed in our laboratory to study flow electrification of oil at a pressboard rectangular duct. As in power transformers, the oil/pressboard couple is insulated from the ground by an oil volume. Pressboard potential, accumulated charges on pressboard surface are recorded and correlated to charge leakage. Index Terms—Electrical double layer, Flow electrification