A study on a mutual grounding impedance and its transient characteristic

Self and mutual impedances of grounding electrodes are experimentally investigated for various grounding arrangements and electrode shapes. A transient induced voltage to an electrode is observed to be similar to transient voltages of the electrode and the inducing one when a step-like current is applied individually. Correspondingly, the frequency characteristic of the mutual impedance evaluated by numerical Fourier transform from the measured voltage and current is similar to that of the self impedance. An equivalent model circuit of the grounding impedance is derived from the frequency characteristic, and an EMTP simulation using the model circuit agrees reasonably well with the measured result.