PROJECT TITLE :

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

ABSTRACT:

Converter transformer plays an vital role in the HVDC transmission system. The valve aspect insulation in converter transformer withstands AC superimposed DC electric field throughout operation. So as to research the flow electrification characteristics of oil-paper insulation below the AC superimposed DC electric field, an oil-paper tube model with concentric cylindrical electrode geometry was engineered in laboratory. Experiment study on flow electrification below DC electric field was carried using the closed oil circulating system, and therefore the influence rule and mechanism of amplitude of AC superimposed DC electric field, the DC part 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 impact with amplitude of applied voltage. The peak purpose voltage decreased with the DC part ratio. The theoretical analysis based mostly on the experiment results demonstrated that ions generation speed at the oil-paper interface relied 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 cause peak impact of streaming currents. Changing of temperature will influence the flow electrification characteristics by affecting the ions migration speed and the electric field distribution within the insulation.