Toshio Sonoda

Experimental study of current-dependent grounding resistance of rod electrode

This paper has experimentally investigated transient behavior of grounding electrode systems especially for a high impulse current up to 40 kA in particular reference with a mutual grounding resistance between the electrodes. The experimental results show that the mutual grounding resistance depends on the applied current similarly to the current dependence of the self-grounding resistance. The phenomenon can be explained by the increase of an effective rod radius and an effective length. The self-grounding resistance greatly depends on the rod dimension and on the soil resistivity for low currents as analytically well known. However, the parameters cause a less effect on the nonlinear characteristic for high currents exceeding 10 kA.

Observation of Lightning Overvoltage in a 500 kV Switching Station

This paper describes observation of lightning overvoltages in a 500 kV switching station at Kansai Electric Power Co., Japan. Three types of lightning overvoltages, such as back flashover, direct lightning hit to a phase conductor, and lightning-induced voltage have been observed. The lightning overvoltages due to a back flashover were lower than operation voltage of a surge arrester. The observation suggests that induced voltage caused by electromagnetic fields radiated from a lightning channel affects lightning overvoltages in a station.