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 (IC) 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.

I. Introduction

Composite towers have been regarded as next-generation towers for transmission lines due to their lower environmental, visual and economic impacts [1]. Compared with traditional transmission towers, the application of a composite pylon can reduce both the line corridor areas and the use of steel [2], decreasing the cost of component transportation and assembly [2]. In recent years, the increase of new renewable energy leads to a growing demand for new overhead lines and towers [3]. A composite pylon, which has a ‘Y’ shape with an integrated cross-arm without insulator strings, is a promising substitute for the traditional transmission tower. A proposal that a bare grounding conductor through the cross-arm is designed as downlead system to provide zero potential for the shield wire. The mast of the pylon body is composed of a vertical steel cylindrical mast with a radius of 1 m. Low-density polyethylene (LDPE) is used as filling material inside the cross-arm to curb the partial discharge and to guarantee enough insulation between phase conductors and downlead [4].