The protection of structures and electrical systems from lightning requires knowledge of the characteristics of electromagnetic fields generated by lightning and of the statistical distribution of lightning current parameters. The statistical distributions of lightning current parameters can be obtained by recording the currents in lightning flashes striking high tower. However, the presence of the tower itself may distort these distributions to some extent and there is always the unresolved question of whether these distributions are valid for lightning flashes striking flat regions. On the other hand, all the information necessary to obtain the characteristics of currents in lightning return strokes is embedded in the lightning-generated electromagnetic fields. However, in propagating from source to measuring station, the electromagnetic fields will change in a number of ways depending on the geometry and the electrical characteristics of the propagation path. For example, in propagating over finitely conducting ground, the electromagnetic fields will lose their higher frequency components. As a result, the amplitude of the electromagnetic field decreases, and the rise time of the electromagnetic field increases with increasing propagation distance over land. When the ground is stratified the propagation effects may enhance or attenuate high frequencies, depending on the conductivity and the depth of the conducting layers.

Inspec keywords: electromagnetic fields; lightning; lightning protection; statistical analysis; electromagnetic wave propagation; current distribution; electrical conductivity; radiation effects; power distribution protection

Other keywords: lightning current distribution; statistical analysis; conducting layers; electromagnetic fields; conductivity; lightning; electrical systems protection; radiation propagation effects

Subjects: Distribution networks