8.1 Introduction

Overvoltages induced by indirect lightning on overhead lines can cause damage to power systems, communication networks and electronic control and management systems. Moreover, due to its more frequent occurrence, indirect lightning constitutes a more important cause of short interruptions and voltage sags than direct strikes, especially for distribution networks. Estimation of indirect lightning is therefore crucial for the correct protection and insulation coordination of overhead lines and, as a consequence, has been the subject of various studies during the past decades. The problem has been seriously reconsidered in recent years due to the increasing demand by customers for good quality in the power supply, and new models have consequently been developed to obtain a more accurate estimation of lightning-induced voltages.

Evaluation of lightning-induced voltages requires knowledge of the electromagnetic field change along the considered line. This electromagnetic field is generally determined assuming that the lightning return stroke channel is a straight vertical antenna above a conducting plane (see Chapter 5). The spatial and temporal distribution of the current along the channel is specified using a return stroke model (see Chapter 6).

In this Chapter, we will present the theory describing the interaction of lightning electromagnetic fields with overhead lines, with particular reference to power systems. In the first part of the Chapter, we will present the different approaches and formulations that can be used to describe the coupling between an external electromagnetic field and a transmission line. Then, we will extend the selected...