Improved contactless measurement of lightning current using printed circuit board differential loop with numerical integral program

The measurement of lightning current plays an important role in the identification of lightning strikes fault and location. However, measuring the lightning current directly, accurately, and safely is difficult. This paper presents an improved contactless measuring method by using a differential loop made of a printed circuit board with a numerical integral program. This differential loop is used to obtain the differential signals of the measured lightning current and consists of a planar circular spiral coil, a coaxial fitting, and an aluminous shielding shell. MATLAB numerical integral program is used to integrate the differential signal to reproduce lightning-current waveforms. Measurement theory, equivalent circuit, frequency analysis, and design of this improved contactless measurement are described. In the laboratory, experiments with three types of impact currents (24/42, 8/20, and 7/20 μs) were adopted to calibrate this improved measurement compared with Pearson coil. The results of the experiments show the following: 1) for a certain measuring distance, the differential loop with a numerical integral program can reproduce the waveform of 24/42, 8/20, and 7/20 μs accurately and completely under an appropriate design; 2) the differential loop retains the advantages of safety, strong anti-interference ability, good linearity and accuracy compared with the differential-integral loop; 3) the improved measurement facilitates the easy unification of stray parameters and breaks the contradiction between sensitivity and low cut-off frequency, which is beneficial in acquiring lightning-current waveforms with low amplitudes.