Pollution performance of HVDC SiR insulators at extra heavy pollution conditions

As an integral part of transmission lines, insulators play a major role in the reliability of power systems and their failure exposes the performance of the whole system into risk. Compared to AC systems, DC static field and corresponding arc without zero crossing makes DC flashover performance more problematic. Although the utilization of composite insulators in HVDC transmission lines continues to grow, there is still a lack of investigation on DC pollution flashover performance of SiR insulators especially at extra heavy pollution conditions. This paper presents the measurement and analytical results for DC flashover of SiR insulators in terms of different polarities of voltage, hydrophobicity levels and geometrical characteristics of SiR insulator at extra heavy pollution conditions. According to the results flashover strength in positive voltage is 4% higher than that in negative voltage. In addition, different profiles of SiR insulators did not show the same pollution flashover sensitivity on hydrophobicity. The empirical modeling of pollution flashover performance of insulators in terms of specific leakage distance, average diameter, form factor and the ratio of shed spacing to shed depth, revealed that specific leakage has the highest impact on pollution-flashover voltage gradient. This is of importance especially for designing and dimensioning of SiR insulators to be used under HVDC voltage.