Validation and revision of far-field-current relationship for the lightning strike to electrically short objects

• Accuracy of far-field-to-current conversion factors for short objects has been validated
• Finite conductivity has much effect on the far-field-to-current conversion factors in some cases
• Revised far-field-to-current conversion factors have a much better accuracy.

In this paper we have validated and revised the general expressions for far-field-current factors presented by Bermudez et al., 2005 and Bermudez et al., 2007 for lightning strike to tall objects on perfectly and finitely conducting ground, respectively. For the perfectly conducting ground, it is found that when the risetime of lightning return stroke current (RT) is larger than 5h/c (h is the height of tall object and c is the light speed), the overestimation caused by the traditional method predicting the lightning current peak is within 10% beyond a distance of 20 km from the lightning channel, and with the decrease of observed horizontal distance d, the error will increase due to the effect of induction field component. For example, when d is 10 km, the overestimation is about 20% for strike to a 300-m-tall object. For the finite conductivity ranging from 0.01 S/m to 0.001 S/m, when the lightning strikes the 300-m-tall object, the lightning current peak predicted from the measured magnetic field peak according to the traditional method is overestimated ranging from about +5% to +20% (positive means overestimation while negative means underestimation) and the derivation value is more within a distance of 20 km because of induction field component; When the lightning strikes the 50-m-tall object, the predicted current peak according to the traditional method has an error ranging from about +5% to −15%.