Influence of corona on lightning-induced voltages on overhead power lines

A model for the calculation of lightning-induced voltages is presented allowing the assessment of the effect of corona when power distribution lines are illuminated by lightning electromagnetic fields. It is shown that, as far as corona can be described by means of an increase of capacitance after the voltage has reached a threshold value, corona can produce an increase in the peak amplitude of the induced voltage. An explanation of this result is given. The need for experimental results to test this theoretical finding is stressed in the paper. It is also shown that for lightning-induced voltage calculations, the ground resistivity plays a more important role than the corona in modifying the wave shape of the induced surges. This is different from the direct-strike behaviour, and is due to the fact that the ground resistivity affects more strongly the lightning-radiated fields rather than the surge attenuation along the line, while corona affects only surge propagation