Interaction of electromagnetic fields generated by lightning with overhead electrical networks

In this chapter, the authors present the theory describing the interaction of lightning electromagnetic fields with overhead lines, with particular reference to electrical power networks. The first part of the chapter, presents different approaches and formulations that can be used to describe the coupling between an external electromagnetic field and a transmission line. Then, the selected field-to-transmission line coupling model was extended to include the effects of a lossy earth serving as a return conductor and to deal with the case of multiconductor lines. The time-domain representation of coupling equations, useful for analysing nonlinearities, was also be dealt with. The experimental test and validation of coupling models using data from natural and artificially triggered lightning, EMP simulators, or reduced scale models were presented in the first part of the chapter. In the second part of the chapter, the illustrated mathematical models were applied to compute lightning-induced overvoltages on overhead power distribution lines. This chapter particularly discussed the influence on the amplitude and waveshape of lightning-induced voltages of: the finite ground conductivity; the presence of shielding wires; the downward leader phase of the lightning discharge that precedes the return stroke phase and; the corona effect.