TRANSIENT IMPEDANCE OF GIS GROUNDING GRID

The transient impedance of a grounding grid for a commercial 550kV GIS was measured on site using steep front currents with rise time from 1 00ns to 2 mu s. From the measured results, it was found that the trans ient impedance of the measured grid for those currents is simulated by a series circuit with an inductance 1 mu H and a resistance 3 Omega. Applying the obtained impedance to the lightning surge analysis, it is pointed out that the grounding condition at an arrester tank end has a remarkable influence on the protecting performance of a surge arrest er.