Analysis of Lightning Overvoltages in Low-Voltage Power Distribution Lines with Service Drop Lines

Lightning outages on high-voltage power distribution lines have been decreased steadily for lightning protection with surge arresters and overhead ground wires for high-voltage power distribution lines in Japan. However the number of lightning outages on low-voltage distribution lines is on the increase for the information-oriented and computerized society. We have examined lightning overvoltages in low-voltage distribution lines with service drop lines for customers. The peak value of the line conductor voltage in a low-voltage line is reduced and the waveform of it resembles that of the neutral conductor voltage due to installing a DV wire and a grounding at the neutral conductor. The service drop line should be taken into account when lightning overvoltages in low-voltage distribution lines is examined. We have studied protection of low-voltage distribution lines against lightning induced overvoltages with the model of low-voltage distribution line using the Electro-Magnetic Transients Program (EMTP) on the basis of the experimental results. Nevertheless the grounding resistance value is higher, separate groundings on the closest pole to a pole transformer and the termination of low-voltage line is as effective as a single low grounding on the middle of low-voltage line.