Generalized pi-circuit tower grounding model for direct lightning response simulation

•A simplified model for lightning transients of tower grounding systems is discussed.•The equivalent non-linear pi-circuit also accounts for soil ionization phenomena.•A GA-based procedure for accurate wide-band synthesis of the pi-circuit is detailed.•Procedure is successfully tested on three existing large tower grounding systems.•Numerical simulations show excellent agreement with complex, detailed models.

Simulation of direct lightning strokes to overhead line towers requires accurate modeling of tower grounding systems. When large-scale statistical simulations are needed (e.g. in backflashover rate assessment), detailed but computationally intensive models are not suitable. This paper presents a genetic algorithm-based procedure to synthesize a generalized pi-circuit model, aimed at simulating the impulse response of complex grounding systems, including non-linear soil ionization, for backflashover studies. The equivalent electrical parameters of the pi-circuit model are determined as functions of soil resistivity for some commonly used grounding systems; the pi-circuit model is then validated by time-domain ATP-EMTP comparison with a complete circuit model, obtaining very good results (worst-case errors do not exceed 3–4%). ATP-EMTP time-domain simulations of direct lightning strokes to overhead lines equipped with the pi-circuit model are also reported, showing an excellent agreement with results yielded by the complete circuit model as well as drastically decreased computation times (up to 3 orders of magnitude).