Thunder Surge

A lightning surge (rai, or kaminari) is a type of external surge caused by lightning. When electrical charge accumulates within a thundercloud and reaches a level that exceeds the insulating limit of the atmosphere, a discharge eventually occurs between the cloud and the ground, or between clouds, and the current is said to reach 20-150 kA). At that time, the abnormally high voltage generated by a direct lightning discharge applied to power transmission lines or communication cables is called a "direct lightning surge." In contrast, the voltage generated by electrostatic or electromagnetic induction affecting cables located near the point of a lightning strike is called an "induced lightning surge." In addition, when lightning strikes a lightning rod and the ground potential rises, the grounding potential of equipment also increases. This can create an abnormally large difference between the cable and the ground, which is called a "lightning surge due to ground potential rise." The energy of a direct lightning surge is enormous, and equipment cannot be protected by surge protectors alone. Some equipment adopts measures in which most of the energy is absorbed by both lightning rods and overhead ground wires, and the remaining energy is absorbed by surge protectors.