Flashover mechanism and laboratory evaluation of polluted insulators under DC voltage.

摘要

HVDC constitutes an economical alternative when huge blocks of power need to be transmitted over long distances.;Factors which influence the mechanism of pollution flashover under dc voltages must be carefully studied if a representative test is to be proposed, as test results are dependent on various factors, such as source capacity. Two test procedures for HVDC insulator testing are currently being analyzed for international standardization: the salt fog procedure and the solid layer procedure followed by steam fog or cold fog for wetting of the pollution layer.;This thesis presents the results or extensive tests conducted to verify the effect of the voltage source on the critical flashover voltage of dc insulators under pollution. Tests, with the solid layer method using the steam fog for wetting of pollution layer, were performed. A data acquisition system was used to record all current pulses above a certain pre selected current level and the corresponding voltage evolution during current pulse duration, which made possible a complete analysis of current pulses and voltage drops characteristics during the flashover process.;The information obtained provides a better understanding of the flashover process of dc insulation under pollution and may be used to improve the existing testing guidelines.;An analysis of a recent model for simulation of the flashover process of polluted dc insulation was performed. The model was used to estimate the flashover voltage for the insulators tested with reasonable results. An improvement of the model has been proposed and verified.