Lightning performance and formula description of a Y-shaped composite pylon considering the effect of tower-footing impedance

This paper presents systematic research on the lightning performance of a novel Y-shaped composite pylon for 400 kV transmission lines and the feasibility of empirical formulas for this kind of tower when considering the effect of tower-footing impedance. The transient overvoltage response to a lightning surge at the tip of the pylon is modeled in PSCAD/EMTDC. Compared with the Donau tower, the composite pylon shows a similar backflash rate (BFR) level. Then, we use qualitative analysis based on lumped parameter model and distributed parameter model to predict the critical flashover current (I-c) of the composite pylon. We find that the calculated results exhibit higher error deflection when the existing empirical formulas are applied in the Y-shaped pylon. Furthermore, the simulated lightning performance has a lower sensitivity to varied tower-footing impedance compared with empirical formula calculation. The special structure of the Y-shaped pylon, the discontinuity in surge impedance and the soil ionization are analyzed to account for the role of tower-footing impedance on lightning performance. Finally, we improve the accuracy of the empirical formulas to the Y-shaped pylon lightning performance and discuss the effect of the footing impedance on the BFR.