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Increase of Static Electrification in Aged Transformers

Increase in static electrification and discharge generation was experienced during the service operation of aged power transformers of both shell and core-form. However, the electrical characteristics of the oil did not demonstrate increase in static electrification. The investigation on the aged oil by measurement of electrostatic charging tendency suggested the possibility that some deteriorated compound in oil was adsorbed to the pressboard and increased the static electrification. However, the measurement of electrostatic charging tendency with the aged pressboard did not demonstrate enough increase, whereas accumulated charge measurement of the aged pressboard confirmed strong increase in static electrification. On the other hand, the measurement of accumulated charge by potential measurement confirmed strong increase of charge accumulation by the pressboard aging. It was suggested that measurement of accumulated charge was suitable for the assessment of static electrification in aged transformers.