Measurements are presented and characterized of vertical electric fields 500 m from artificially initiated lightning return strokes and of voltages induced at both ends of a 448 m distribution power line by the same discharges, which are about 20 m from one end of the line. The experiment, which took place during the Summer of 1986 at the NASA Kennedy Space Center, is described. The measured line voltages could be grouped into two categories, those in which multiple, similarly shaped, evenly spaced pulses were observed, which we call oscillatory, and those dominated by a principal pulse with subsidiary oscillations of much smaller amplitude, which we call impulsive. Voltage amplitudes range from tens of kilovolts for oscillatory voltages to hundreds of kilovolts for impulsive voltages. Contrary to what was expected, the voltage at the transmission line end farther from the lightning was found to be considerably larger than the voltage at the end nearer to the lightning.;A new technique is derived for the calculation of the electromagnetic fields from nearby lightning over an imperfectly conducting ground. This technique is used in conjunction with a time domain coupling theory to calculate voltages at either end of the line. The results show fair agreement with the measured oscillatory voltage waveforms if corona is ignored and improved results when corona effects are modelled. Reasonable wave shape agreement is obtained for voltages of the impulsive type when these are modelled by the introduction of non-linear flashover effects, although unrealistically high return stroke currents are required to obtain good amplitude agreement. Suggestions for future experiments are given in the light of the present experience in measuring electric fields and their associated voltages from very close lightning.
展开▼
