Method for Measuring Impulse Grounding Resistance under Different Current Waveforms Based on Time-frequency Transform

Accurate measurement of the impulse grounding resistance of the grounding device is important and necessary for ensuring the reliability of the power system. Existing research shows that the impulse grounding resistance is related to the impulse current waveform. In this paper, based on the time-frequency transformation, the frequency-domain decomposition method that can obtain the impulse grounding resistance under any impulse current waveform is proposed. Firstly, by analyzing different impulse current waveforms in the frequency-domain, it is found that the main frequency ranges of different lightning current waveforms are all below 1 MHz according to the proportion of frequency components. It is suggested that by measuring the grounding impedance of specific frequencies, the spectrum curve of the grounding device can be obtained by interpolation. According to the characteristics of the injected current waveform, the corresponding voltage response of the grounding device is obtained through inverse Fourier transform, and its impulse ground resistance is further obtained. As is shown in the simulation and experimental results, without considering the spark discharge, the error of measuring the impulse grounding resistance of the grounding device between the frequency domain decomposition method and the measurement with impulse generator is within 5%.