Measurement and Analysis of Impulse Grounding Impedance for UHV Transmission Tower

In this paper, application of a portable instrument to gain impulse grounding impedance (IGI) characteristics for grounding device (GD) of ultra-high-voltage (UHV) 1000 kV transmission towers is introduced. The test currents of 8/20 $\mu$ s and 10/350 $\mu$ s were chosen as the injection signal sources to the grounding device respectively, while the response transient voltage waveforms in time domain were simultaneously measured. Then the corresponding IGI can be calculated with processing of the impulse current and voltage waveforms. In order to obtain the transient characteristics of the whole test process, the transient grounding resistance in time domain (TGRT) and transient grounding resistance in frequency domain (TGRF) are also analyzed and compared abased on the measured current and voltage waveforms of 8/20 $\mu$s and 10/350$\mu$ s respectively. All of that provides a reference for basic research of lightning protection for the UHV 1000 kV transmission towers and a better understanding of transient characteristics of GD under the lightning stroke.