Pollution Flashover Characteristics of Hydrophilic Surface Under Superimposed AC/DC Voltage

Insulation devices in the flexible high-voltage direct current (HVdc) transmission system couple a specific ac component. To reveal the pollution flashover characteristics of hydrophilic surfaces under superimposed ac/dc voltage, this article designs a power supply system capable of generating superimposed voltage and conducts artificial pollution flashover tests on glass specimens. Under superimposed voltage, the arc development speed before flashover is faster, and the arc extinguishing and reignition phenomena occur even without a zero-crossing point. The ac component of the pollution flashover voltage decreases with the dc component superimposition, and this impact diminishes as pollution increases. When described as a peak value, the difference in flashover voltage under the same pollution degree is within 6.7% for different voltage configurations, while in terms of root-mean-square (rms) value, the difference ranges from 13.8% to 19.8%. The difference in flashover voltage under superimposed ac/dc voltage is also related to power supply characteristics, especially for heavily polluted surfaces. These results provide references for external insulation configuration in flexible HVdc projects.