Oil-paper Interface Research Articles

Flow electrification characteristics of oil-pressboard insulation under ac superimposed on DC electric field

Converter transformer plays an important role in the HVDC transmission system. The valve side insulation in converter transformer withstands AC superimposed DC electric field during operation. In order to investigate the flow electrification characteristics of oil-paper insulation under the AC superimposed DC electric field, an oil-paper tube model with concentric cylindrical electrode geometry was built in laboratory. Experiment study on flow electrification under DC electric field was carried using the closed oil circulating system, and the influence rule and mechanism of amplitude of AC superimposed DC electric field, the DC component ratio and oil flow velocity on the flow electrification was analyzed. The experiment results demonstrated that influences of oil flow velocity and amplitude of applied voltage on streaming currents were related to temperature. At low temperature the streaming currents increased linearly with flow velocity and amplitude of applied voltage. Increase the DC component ratio enhanced the streaming currents. At high temperature the streaming currents increased exponentially with flow velocity and showed peak effect with amplitude of applied voltage. The peak point voltage decreased with the DC component ratio. The theoretical analysis based on the experiment results demonstrated that ions generation speed at the oil-paper interface depended on the dissipation speed of positive and negative ions. Saturation of negative ions migration current in the paper and leakage current at the outer electrode lead to peak effect of streaming currents. Changing of temperature can influence the flow electrification characteristics by affecting the ions migration speed and the electric field distribution in the insulation.

The effect of an oil-paper interface parallel to an electric field on the breakdown voltage at elevated temperatures

Results are reported for the measurement of the electrical breakdown location in the vicinity of an oil-paper interface over the temperature range from room temperature to 150 degrees C. The data indicated that the electrical breakdown occurred at the interface from 15% to 43% of the time, depending on the details of the particular set of measurements. A theoretical analysis shows that this experimental result is consistent with the electric-field enhancement, the area over which the enhancement occurs, and the spread in the breakdown voltages for nominally identical tests. >

Electrical Breakdown in Composite Insulating Systems: Liquid-Solid Interface Parallel to the Field

The location of electrical breakdown in a composite insulating system has been measured. In these experiments, a paper sample was mounted so that it connected the two electrodes. Electrode structures ranging from plane-plane to sphere sphere were used. The electrode-paper system was tested in oil to determine the properties of an oil paper interface. The data indicated that, in a carefully prepared system, the breakdown will not necessarily occur at the interface. In addition, it was found that breakdown voltages were not significantly lower for those breakdowns which occurred at the interface than for those which did not. It was noted that if the paper was not dried or if many gaseous voids were left in or on the paper, the breakdown regularly occurred at the interface and at a lower voltage.