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).