Transient surge impedance of a vertical conductor over the ground

This paper presents an investigation into transient surge impedance of a vertical conductor over the ground during a lightning stroke. An equivalent circuit approach (PEEC) is employed to evaluate path-independent voltage on the conductor. The transient surge impedance is then computed in time domain until the reflected surge is back to the observation point. It is found that transient surge impedance increases as time goes on, and is determined by geometry of the conductor and waveform of the injected surge current. The transient surge impedance is neither affected by conductor height nor grounding resistance. The presence of a ground has no effect on transient surge impedance. A comparison with the approximate formulas for characteristic surge impedance is also made in the paper. The difference varies significantly with conductor height for the surge current with a long rising time.Department of Building Services Engineerin