The design and optimization of the down-lead system for a novel 400 kV composite pylon

This paper presents systematic research of a grounding down-lead design and its optimization for a novel Y-shaped composite pylon. A grounding down-lead inside the cross-arm is proposed as a potential grounding method. The transient response to lightning surges is modeled in PSCAD/EMTDC for a flash of lightning striking at the tip of the pylon. Aiming at the characteristic of the pylon structure, we propose theoretical formulas to calculate the surge impedance of the inclined down-lead circumscribed by composite materials. Besides, potential multi-factors affecting BFR such as the configuration as well as the length of the down-lead, the pylon span, the dielectric constant of the filling material, the electromagnetic propagation speed of the lightning, and the capacitances between down-lead and phase conductors are investigated, after which the grounding lead system of the pylon and filling materials are determined. Afterwards, the applicability of the multi-down-lead system to increase critical current (Ic) is discussed considering the lightning current capacity and the corona generation. Finally, we verify the insulation of the down-lead system. Compared with that of traditional Eagle and Donau towers, the backflashover rate (BFR) of the Y-shaped pylon with an optimized down-lead system is lower than that of traditional ones.