Estimation of Lightning Incidence to the Cahora-Bassa HVDC Overhead Lines based on Stochastic Modelling of Lightning Attachment

Abstract:
The lightning performance of the ±533 kV Cahora-Bassa HVDC overhead lines is investigated. A stochastic lightning attachment model is employed to estimate lightning incidence to the lines, simulating the lightning discharges propaga-tion considering their fractal characteristics. The effects of the operating voltage and polarity of the line pole conductors are demonstrated on lightning incidence results; these parameters are neglected by the conventional electrogeometric models. Based on stochastic model results, shielding failure currents that cannot be predicted by the classical electroge-ometric analysis are computed; these can possibly explain lightning currents along the HVDC lines causing power faults recorded in field observations along the negative and positive poles. The total lightning flashover rate is also computed by considering the corresponding shielding failure flashover and backflashover rates. It is shown that the total flashover rate of the positive pole is significantly higher than that of the negative pole; this is in accordance with field records from the investigated lines.