surge

A lightning surge (Rai or Kaminari) refers to a type of externally generated surge caused by lightning. When electric charge accumulates within a thundercloud and reaches a level that exceeds the limit for adiabatic compression by the atmosphere, a discharge occurs either between the cloud and the ground or between clouds. It is said that this current can reach 20-150kA. When abnormally high voltage generated by a direct lightning discharge is applied to power lines or communication cables, it is called a "direct lightning surge." In contrast, voltage generated by electrostatic or electromagnetic induction to those cables near the lightning strike point is called an "induced lightning surge." Also, 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 amount of energy in a direct lightning surge is incredibly enormous and cannot be mitigated by surge protectors alone. Some equipment takes measures to absorb most of the energy using both a lightning rod and an overhead grounding wire, and absorb the remaining energy with the surge protector.