• Energy Research

Surge arresters may represent an efficient choice for limiting lightning surge effects, significantly reducing the outage rate of power lines. The present work firstly presents an efficient numerical approach suitable for insulation coordination studies based on an implicit Crank–Nicolson finite difference time domain method; then, the IEEE recommended surge arrester model is reviewed and implemented by means of a local implicit scheme, based on a set of non-linear equations, that are recast in a suitable form for efficient solution. The model is proven to ensure robustness and second-order accuracy. The implementation of the arrester model in the implicit Crank–Nicolson scheme represents the added value brought by the present study. Indeed, its preserved stability for larger time steps allows reducing running time by more than 60 % compared to the well-known finite difference time domain method based on the explicit leap-frog scheme. The reduced computation time allows faster repeated solutions, which need to be looked for on assessing the lightning performance (randomly changing, parameters such as peak current, rise time, tail time, location of the vertical leader channel, phase conductor voltages, footing resistance, insulator strength, etc. would need to be changed thousands of times).

We investigate the improvement of the lightning performance of overhead power lines through the use of additional ground wires placed below the phase conductors. The analysis of the electrical system is carried out through a method based on the conventional multiconductor transmission-line formalism. In the presence of a direct lightning, both the currents flowing in phase conductors and ground wires and the overvoltages across insulator strings can easily be evaluated. The main effects of such additional ground wires are here pointed out through an accurate numerical analysis.