Calculation of the local ground-level total electric field near a tower in a multi-circuit AC-to-DC conversion project based on an improved upwind finite element method

To address the problems of complex ion-flow space-charge distribution in AC-to-DC converted transmission lines under wind action, and the tendency of the conventional upwind finite element method to suffer from iterative oscillations and convergence difficulties, this paper proposes an improved upwind finite element method that enhances the stability of ground-level total electric field calculation under complex wind conditions. Taking a typical multi-circuit project where 750-kV AC cup-shaped towers are converted for 500-kV DC transmission as the engineering background, the local ground-level total electric field near one converted tower is investigated under different wind speeds and three-conductor polarity arrangements. The results show that the proposed method exhibits better convergence performance than the conventional upwind finite element method. An increase in wind speed promotes the wind-driven transport and redistribution of space charge, thereby affecting the peak magnitude and location of the local ground-level total electric field. The conductor polarity arrangement significantly influences the local field distribution, with the positive-positive-negative arrangement yielding a higher field magnitude among the investigated local configurations. The findings can provide a reference for local electromagnetic-environment assessment near towers in similar AC-to-DC conversion projects.