Electrostatic charging tendency of insulating fluids

Summary form only given, as follows. Catastrophic failures of very large forced-oil-cooled power transformers continue to occur, with evidence linking static electrification to the probable cause. Charge generation and separation process at the inner surface of the liquid/solid interface of cooling ducts as well as paper insulated high voltage windings are one reason for the electrostatic charging phenomena. The charging behavior of insulating fluids has been tested in this study. The method used is an adaptation of the Mini-Static Test (Oommen and Petrie, Westinghouse Electric Corp.). This method, which allows measurement of the charge separated by flow through a paper filter, is fast and relatively simple for comparing the charging tendencies of different insulating fluids. Different commercially available insulating fluids (new and used) have been evaluated for their electrostatic charging behavior. Experimental and theoretical studies of characteristics influencing the process of charge generation (resistivity, dielectric dissipation factor, interfacial tension, flow rate, water content, cellulose particles) are focused in this paper. The effects of storage in various containers (e.g. glass, metal) on the electrostatic charging tendency of oils have been investigated