Lightning Electromagnetic Fields above Perfectly Conducting Ground: a review

Lightning may be the cause of outages and faults on electrical infrastructures. In overhead distribution lines, voltages overcoming the critical flashover value of the line may be induced by indirect lightning strikes, and this fact may cause serious damages to insulators. Consequently, the assessment of induced voltages is an important aspect in the design phase of transmission and distribution lines. To this goal, the lightning current shall be modeled, the electromagnetic fields should be evaluated and the field-to-line coupling equations implemented. In case time dependent functions are considered, the lightning electromagnetic fields may also be numerically approximated, but, usually, such approximation requires significant computational efforts and strongly depend on the way in which the lightning channel is modeled and on the soil properties. The present paper proposes an overview of the most utilized methodologies aiming at numerically or analytically approximating the lightning electromagnetic fields. Under the hypothesis of perfectly conducting ground, the classical formulation, requiring numerical integration is firstly presented. Then, the most effective approaches aiming at reducing computational timings are discussed. Finally, the models available to represent the lightning tortuosity are presented.