Effects of the impedance of lightning earthing path on lightning currents are investigated by computer simulation. Distributed-circuit models with adequate values of inductance, resistance and capacitance are chosen to represent the lightning channel, upward leaders and the lightning protection system (LPS). Both the currents and voltages as a function of time and height are simulated. Results show that for a lightning stroke without an upward leader, the lightning current is generated at the channel base and then propagates upward as its amplitude decreases. For the case with an upward leader, however, the return stroke current appears firstly at the connecting point of the upward- and downward- leaders, and then propagates bi-directionally down and up as its amplitude decreases. The existence of an upward leader makes both the lightning current and the rate of change of the current at the channel base smaller than with no an upward leader. For a LPS with larger resistance and inductance, the lightning current through it would be smaller but the larger voltage across it would increase the risk of flashover. However, a LPS with larger capacitance can make the lightning currents smaller without increasing the risk of flashover. The results can be used to improve the design of LPS.
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