Characteristics analysis of the induced overcurrent generated by close triggered lightning on the overhead transmission power line

Techniques of artificially-triggered lightning have provided a significantly useful means to directly measure various physical parameters of lightning discharge and to conduct research on protection methods of lightning electromagnetic pulses. In this study, using capacitive and resistive dividers, current probes and optical fiber transmission devices, we measured and analyzed the induced overvoltage on the overhead transmission line and the overcurrent through Surge Protective Devices (SPD) when a lightning discharge was artificially triggered nearby on August 12, 2008 at Conghua Field Lightning Experiment Site. The triggered lightning discharge contained an initial current stage and eight return strokes whose peak currents ranged from 6.6kA to 26.4kA. We found that overcurrents through SPD were induced on the power line both during the initial continuous current stage and the return stroke processes. During the return strokes, the residual voltage and the current through the SPD lasted up to the ms (millisecond) range, and the overcurrents exhibited a mean waveform up to 22/69 mu s with a peak value of less than 2kA. Based on the observed data, simple calculations show that the corresponding single discharge energy was much greater than the values of the high voltage pulse generators commonly used in the experiments regulated for SPD. The SPD discharge current peak was not synchronous to that of the residual voltage with the former obviously lagging behind the latter. The SPD discharge current peak was well correlated with the triggered lightning current peak and the wave-front current gradient. The long duration of the SPD current is one of the major reasons why the SPD was damaged even with a big nominal discharge current.