Coordination of surge protective devices using the current data from lightning field measurements

Since about 15 years the electric and magnetic fields radiated by lightning have been measured in the region of Munich/Germany From these measurements the maximum current steepness of positive and negative return strokes to ground were derived. It was found that the positive return strokes contain higher current steepness than the negative ones. In low-voltage power distribution systems the concept of lightning protection zones requires that surge protective devices are installed, whenever an electrical line crosses the boundary between two zones. Because the maximum current steepness ofnegative strokes is lower than for positive strokes, it can be concluded that for the coordination of the surge protective devices only the negative return stroke currents have to be considered.