Assessment of Lightning Shielding Performance of a 400 kV Double-Circuit Fully Composite Transmission Line Pylon

Modern day overhead transmission lines are taking a giant leap in modernization, with the change in power generation from fossil fuels to renewable sources such as solar power, hydro power and wind power. The renewable generation needs to be connected to a large scale high voltage transmission grid. In Europe alone, 28.000 km of 400 kV transmission line is needed by 2020 to fulfil the aim of providing 20% of Europe’s energy from green energies. It means that more than 100.000 new pylons will be needed [1]. For this reason, the next generation of overhead line is introduced, by developing new design pylons that are easier to erect, less costly, smaller and environmentally more feasible than the old ones, which is important to get public acceptance. In this regard, a fully composite pylon for 400 kV overhead transmission lines is presented with a new innovative design concept shown in Figure 1.
The integration of insulators in the cross-arm design is the prominent feature of the fully composite pylon in comparison with conventional towers. The unibody cross-arm of the pylon is expected to have 30 degree inclination and all conductors are fixed to the top of the cross-arm by cable clamps or special high-quality insulation sections. Thus, the configuration of phase conductors on the cross-arm is in the form of diagonal and differs from other widely used configurations in overhead transmission lines i.e. horizontal, delta and vertical configurations.
Unlike traditional steel lattice towers, the composite pylon does not provide access to ground potential due to its non-conductive materials. Therefore, the lightning shielding of pylon and conductors requires a ground potential access to shield wires by utilizing a ground cable inside the hollow cross-arm and pylon body.
Efficient design of a lightning shielding system for the fully composite pylon is one of the major challenges in the electrical design of the pylon which also has to be considered in terms of mechanical and material designs. The other challenges are determination of air clearances and design of shed profiles on the unibody cross-arm which are discussed in [2] and [3], respectively. In this paper, the weaknesses and strengths of the preliminary assigned shielding angle for the pylon are investigated and subsequently, the shielding failure rate of the line is derived from the electro-geometric model (EGM).