Flow electrification characteristics of typical plane oil-pressboard insulation under AC/DC voltage

Due to the special working condition of converter transformer, the valve winding withstands both AC voltage and DC voltage during the operation. In order to investigate the flow electrification characteristics of the oil-pressboard insulation in converter transformer under AC superimposed DC voltage, the experiment research on flow electrification under AC superimposed DC voltage was carried out with the typical plane oil-pressboard insulation structure. The results show that the characteristics of streaming current under AC superimposed DC voltage was related to insulating oil flow velocity, applied voltage amplitude, temperature and the proportion of DC component ratio. With the temperature increases, the relationship between streaming current and velocity was changing from linear relationship to power function. The applied voltage has great influence on the streaming current, and the streaming current increases first then decreases with applied voltage. The voltages corresponding to the peak current increase with insulating oil velocity, and decrease with the DC component ratio. Theoretical analysis of the test results show that the acceleration of the migration of negative ions in the paper under the applied electric field lead to the streaming current increase. The magnitude of streaming current is decided by both migration current and leakage current under electric field.