Influence of Bandwidth, Resolution, and Oscillations on Lightning Current Measurement Accuracy

Abstract:
Lightning current measurement plays an important role in lightning research. The current is usually measured with a bandwidth whose upper limits range from 200 kHz to 20 MHz, and is digitalized at 8 bits to 14 bits. In this study, we propose a new approach to analyze the impact of the measuring bandwidth and digital resolution on the current measuring accuracy for the first time. The approach is then applied to three typical lightning current impulsive waveforms defined in IEC 62305-1:2010 and one typical lightning current oscillating waveform observed on a tall tower. To evaluate the current measuring accuracy versus the measuring bandwidth and the digital resolution for a given current waveform, four parameters are defined, namely, the current peak, electric charge (current integral), specific energy (current square integral), and the maximum current-derivative. For the waveforms analyzed, it shows that the current measurement accuracy is poor when the bandwidth is less than 2 MHz and is good enough when the bandwidth is above 5 MHz at a digital resolution of 10 bits. This result could help us to make an adequate standard for lightning current measuring system.