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Electrical performance evaluation of EHV post insulators covered with ice under different air gap configurations

This paper investigates the influence of air gaps on the maximum AC withstand voltage (VWS) of ice-covered post insulators, typically used in Hydro-Quebec 735-kV substations. The VWS was experimentally determined based on IEEE Standard 1783, under icing conditions. The results reveal that the number of air gaps affects the VWS significantly. The configuration with four air gaps allows improving the VWS by 15% in comparison to the configuration with three air gaps. Moreover, high speed video camera techniques were used to observe the mechanism of electric arc propagation over ice surface with respect to the air gap configuration. Also, to interpret the performance of the ice-covered insulators with different air gap positions, the voltage and electric field distributions along the ice-covered insulator were simulated numerically by the Finite Element Method (FEM) during the melting period. The simulation results confirmed that increasing the number of air gaps improves satisfactory the uniformity of voltage distribution of the EHV post insulators and consequently the maximum withstand voltage. Based on the obtained results, the installation of booster sheds to improve the insulating performance of post insulators under icing conditions was recommended.