Measuring Impulse Grounding Resistance by Multi-Frequency Combination Method

To measure the impulse grounding resistance of transmission line towers accurately, a multi-frequency combination measurement method based on Fourier transformation is proposed. Firstly, a standard lightning impulse waveform was extended as a periodic function. This function was then expanded as a trigonometric series via Fourier transformation. Frequencies of the fundamental wave and harmonics were thus obtained, and amplitude and phase of relationships between the measured source and corresponding Fourier series terms were described. Through scaling and phase shifting, the measuring results were converted to a response function of Fourier Series terms using different frequency components. The impulse response waveform was obtained via the inverse Fourier transformation, yielding the impulse grounding resistance. The effect of the number of Fourier Series terms on the impulse grounding resistance was analysed. It is found that if the number increases from 50 to 120, the deviation between measurement and simulationresult drops from 21% to 9%. Finally, physical experiments have verified that this adopted method is consistent with the direct impact power measurement results. Experimental results show that under the same measuring connection mode, the difference between the measuring result presented here and that of the percussion device is less than 10%.