Protection Measures for Lightning Overvoltages in a Low-Voltage Dc Power Supply System

In the pursuit of a carbon-neutral society, direct current (DC) power supply systems are gaining attention as highly efficient low-voltage wiring systems. This study uses electromagnetic-field analysis to investigate overvoltages that occur in low-voltage wiring owing to lightning strikes on buildings equipped with DC power supply systems. When a building is struck directly by lightning, current flows from the structure to the grounding line of the low-voltage wiring. We have confirmed that the lightning overvoltages that occur in the distribution board are induced by the loop inductance of the low-voltage wiring and the time rate of change of the current flowing through the grounding line. Therefore, to reduce overvoltages, it is crucial to mitigate the current flowing into that grounding line by considering the flow of the lightning current through the structure when determining the connection point of the grounding line. For example, by moving the connection point with the structure away from the lightning strike point, the steepness of the current flowing through the grounding line can be reduced, thereby suppressing overvoltages.