Lightning is a widely recognized source of damage and disruption to electrical power systems worldwide. The climate is changing, with both natural and anthropogenic origins. This chapter is concerned with the response of lightning to changes in temperature and aerosol loading of the atmosphere that are expected to accompany climate change. In the present climate, lightning is shown to increase with both temperature and with the boundary layer populations of cloud condensation nuclei (CCN). In a future climate characterized by the continued consumption of fossil fuels, the threat from lightning is expected to increase.

Return stroke models are used in the calculation of lightning-induced over-voltages in power lines because the electric and magnetic field as a function of distance and height along the line is difficult, if not impossible, to obtain experimentally. Thus the return stroke models should represent faithfully the electric and magnetic fields generated by lightning first and subsequent return strokes, the events that induce largest over-voltages in power systems. Following an introduction and nomenclature, the reader is introduced in Sections 3.2, 3.3 and 3.4 to the various concepts used by engineers (i.e. current propagation, current generation and current dissipation) to construct engineering return stroke models. In Section 3.5, the way in which any given return stroke model could be represented as a current generation or current dissipation type is described. After showing that current propagation concept is a special case of current dissipation concept in Section 3.6, the way in which the current generation and current dissipation concepts could be combined to obtain return stroke models that are in agreement with current pulse propagation along transmission lines in the presence of corona is presented in Section 3.7. In Section 3.8, a review of the basic features of electromagnetic fields of return strokes that are being used in testing the engineering return stroke models are presented. This section is followed by a description of the evaluation of electromagnetic fields, including the horizontal electric field, from return stroke over finitely conducting ground. The chapter ends with concluding remarks.

Lightning is the main cause of unscheduled interruptions in overhead power lines, affecting reliability of power supply and thus, consequently, resulting in economic losses. Lightning-caused insulation flashover in overhead power lines is associated with the fast-front overvoltages across line insulation, arising due to direct lightning strokes or induced by nearby lightning. Shielding against direct lightning strokes to phase conductors of overhead power lines is provided by shield wires. The latter are metallic elements that are able to, by physical means, launch a connecting upward discharge that intercepts the descending lightning leader from a distance, called striking distance, commonly also called attractive radius or lateral distance. Lightning leaders intercepted by shield wires, increasing the potential of the transmission-line tower, may result in power-line outages due to backflashover, that is, insulation flashover between tower and phase conductors. However, some of the less intense lightning strokes, not being intercepted by shield wires terminating thus to the phase conductors, may cause powerline outages due to shielding failure. In addition, descending lightning leaders which are not intercepted by the line conductors, striking to ground nearby the power line or to adjacent structures may result in power-line outages due to induced voltages on line conductors causing insulation flashover. As the line operation voltage increases, a higher line insulation level is utilized, and the lightning performance of overhead power lines becomes increasingly determined by the direct stroke flashover rate. In this chapter, the physical process of lightning attachment to overhead power lines is presented and discussed. Engineering models of lightning attachment are described in detail. Finally, a general procedure for the estimation of lightning incidence to overhead power lines is presented.

A grounding electrode consists of any buried metallic body responsible for dispersing current to the soil. The specific application has significant influence on the electrodes' arrangement and dimension. The arrangement can vary from a simple rod, connected to the transformer of a distribution line, to horizontal electrodes buried about 0.5 m deep in the soil composing the counterpoise wires of transmission-line tower footings, or the typical grounding grids of power system substations. The flow of lightning -related currents to the ground and ensuring safety conditions, in terms of distribution of the electric potentials over the ground in the region where electrodes disperse lightning currents into the soil.

The aim of this chapter is to present and discuss models of power transmission line components for the calculation of lightning overvoltages on transmission lines due to direct lightning strikes. The models presented in this chapter are based on lumped- and distributed-circuit theory.