An ATP-EMTP Monte Carlo procedure for backflashover rate evaluation: A comparison with the CIGRE method

• A Monte Carlo procedure for ATP-EMTP backflashover rate evaluation is presented.
• Statistical treatment includes lightning waveforms and line insulation.
• A simplified nonlinear model of tower grounding system lightning transients is used.
• Three physically large, real tower grounding systems are simulated in the paper.
• Comparison with CIGRE simplified and complete method is presented and discussed.

The paper presents the application of an ATP-EMTP Monte Carlo procedure for backflashover rate (BFOR) evaluations to HV overhead lines (OHL), equipped with three different types of spatially extended and/or geometrically involved tower grounding systems. The ATP-EMTP circuit model of the OHL includes detailed line insulation and lightning representation; grounding systems are simulated by a new and simplified model which reproduces the effects of propagation along the ground conductors and soil ionization phenomena. The statistical variables include lightning stroke parameters (polarity, peak current, front and tail times), lightning location, as well as line insulation withstand and phase angle of the supply voltage. An external software engine generates all the required statistically-oriented ATP-EMTP input data, sequentially launches and manages ATP simulations and finally post-processes the results. A good performance in terms of convergence and computation times is evidenced. Results are compared to those yielded by both the simplified and ‘complete’ CIGRE methods for backflashover rate calculations, showing the applicability of the proposed procedure to line configurations characterized by complex tower grounding arrangements.