Effect of corona and non-linear tower grounding system modelling on backflashover simulation

The paper deals with the integration of ATP-EMTP models representing grounding system nonlinearities and corona effect in a wider overhead line (OHL) model, for the main purpose of backflashover (BFO) transient simulations. All towers of the simulated 10 km stretch (25 spans) of a typical 150 kV - 50 Hz Italian OHL have been equipped with a pi-type simplified grounding system model, reproducing transient behaviour including soil ionization phenomena. A MODELS-controlled lumped-parameter model block has been introduced to simulate corona effect on shield wire and on phase conductors, at 50 m intervals along the OHL. The behavior of the proposed corona model is in good agreement with the tests available in the literature. For the BFO simulations presented in this paper, related to direct lightning strokes to tower peaks and to the shield wire, the complete OHL model has provided consistent results with the expected behavior of the transmission lines under lightning surge conditions: results show that the corona effect may influence the BFO for tower strokes while it has a negligible influence for mid-shield wire strokes.