Measurement of Currents Induced on Overhead Line From Very Close Natural and Triggered Lightning

Induced currents on an overhead line due to a natural lightning with a strike distance of 20 m and a triggered lightning with a strike distance of 8 m were analyzed in time domain, frequency domain, and time-frequency domain, respectively. The results indicated that the energy peak of most currents lagged far behind its time-domain peak. The arrival time of different frequency components of the induced currents varies nonmonotonically with respect to frequency, especially that of the currents caused by the natural lightning. The energy of the highest frequency component is not necessarily the strongest. When it occurs earlier than the time-domain current peak, the protection measures designed by referring the time-domain threshold voltage may not start as expected, and accidental damage that may be incurred owing to that energy in the higher frequency band is more easily coupled to the terminal. Compared with the natural lightning, the smaller time delay between current peak and its energy maxima is yielded in the triggered lightning, as well as the shorter duration time of both time-domain current profile and energy distribution. Additionally, the consistency among currents induced by the triggered lightning is better than that excited by the natural lightning.