Flow electrification properties of certain high charging polymeric materials in transformer oil

Large power transformers with high charging oils have been reported and studied in the past twenty years. Several transformer failures worldwide have been attributed to streaming electrification. In most cases the transformer oil has been found to have high electrostatic charging tendencies (ECTs). Many attempts have been made to identify the charge producing compounds, but no conclusive identification has been made. Most of the trace polar impurities present in the oil are mostly non-charge producing, though few have been recognized to increase charging tendency. This paper reports some polymeric materials that are sparingly soluble in oil, yet would produce high charging tendencies with only moderate increase in electrical conductivity of the oil. The polymers studied belong to the family of acetals specifically polyvinyl formal and polyvinyl butyral formulations, some of which find application as magnet wire insulation and other coating formulations. Only the polyvinyl butyrals showed high ECT in oil. The mechanism of charge separation with these materials is not understood