Characteristics of earthing systems under lightning surges

Overvoltage protective devices such as surge arresters and protective gaps are used to divert high lightning surges from line to earth through an earth electrode. An effective design of earthing systems is therefore important to dissipate fault current to earth effectively regardless of the type of fault. The characteristics of earthing systems at power frequency, low-voltage and lowcurrent magnitudes have been extensively researched and fairly well understood. However, the behaviour of earthing systems under transient conditions is still not fully clarified. This paper is to provide a better understanding of the characteristics of earthing systems under lightning impulse, as well as to present an informative review on previous work on soil ionisation phenomena under high impulse currents