A New Approach for Considering the Effect of the Power-Frequency Voltage on the Calculated Lightning Performance of Transmission Lines

The effect of power-frequency voltage on the backflashover rate of 138 kV to 500 kV transmission lines was assessed by means of an elaborate computational approach, based on the Monte Carlo method. Accurate results were obtained using this approach and were taken as reference for assessing the quality of results of the main methodologies available in literature for considering this effect that significantly increases the backflashover probability. The results showed that the effect is more pronounced for low tower-footing grounding impedances and for transmission lines with higher voltage level. With the exception of the approach recommended by CIGRE Brochure 63, the other tested approaches showed to yield reasonable results. Two new alternatives were proposed in this work for considering the effect. Particularly, the work developed an impactful original result: the use of a simple 0.88-multiplying factor to correct the critical currents. This approach yielded top-quality results, exhibiting very small average error (1.2%) and lowest maximum error (9.2%) in relation to the reference results.