Evaluation of analytic formulations for surge impedance calculation of tall transmission towers

Abstract

An analysis of analytic tower models is proposed for simulation of electromagnetic transients in transmission lines supported by towers up to 300 m height. A careful analysis is required for emergent technologies in transmission systems composed of line sections supported by tall towers, with more than 200 m, as recently constructed in the Brazilian Amazon region and across the Yangtze River in China. Usually, conventional towers are modeled using simplistic geometrical forms and analytic formulations. This paper proposes an evaluation of well-established analytic models for representation of transmission towers with more than 50 m height. The analysis is carried out based on reference values of surge impedance obtained by using the Finite Element Method – FEM for towers up to 300 m height and then compared to existing analytic models based on the tower representation by cylindrical form. The reference model is developed using a FEM-based multiphysics software, where the tower can be drawn following the original design of its steel structure. The comparison between these two different modeling techniques is presented as a function of the tower height, surge impedance calculation and electromagnetic transient simulations in the time domain. From the proposed analysis, the most adequate tower models can be determined for analysis of the lightning performance in power transmission systems composed of tall line sections.