Lightning Strike to a Tall Grounded Object: Part 1. Circuit Modeling With Direction Dependence

This paper proposes a circuit model of a lightning strike to a tall grounded object. The model can consider the direction-dependent attenuation characteristic of current propagating along with a tall grounded object as well as frequency-dependent characteristics of lightning channel and tower impedances, in contrast to the conventional lossless transmission line representations. Hence, the model removes the use of an unrealistic high grounding impedance for approximately expressing the significant current attenuation propagating upward along with the tall object. Measured lightning currents at a height of about 500 m of the 634-m-high Tokyo Skytree are accurately reproduced with the proposed model, which assumes a constant lightning channel impedance with a current source that generates a current waveform decaying with time, or a frequency (time) dependent lightning channel impedance with a step-like voltage source. The proposed model can also be used for lightning electromagnetic pulse calculations.