Charge behavior in flowing charged oil/pressboard composite insulation system based on electric field measurement

Electrostatic charging may occur in oil immersed power transformers because of a flow electrification phenomenon. In this paper, we directly measured the time variation of electric field strength in the flowing charged oil using an electro-optic Kerr effect to clarify the charge behavior in the flowing oil/pressboard (PB) composite system. We discussed the measurement results from the viewpoint of charge behavior. Finally we found that the charging process is dependent on the three different electric fields, i.e. applied field, space charge field and counter field by accumulated charges, and is finalized by the balance of these fields.