On the Calculation of Electrical Surges in Underground Cables due to a Direct Lightning Strike

When a building is struck by lightning, the lightning current travels through its reinforcement and along the lightning channel, generating a transient electromagnetic field. A part of the current reaches the ground termination system and the other part is distributed among the cable ducts and soil-containing conductors leading away from the building. Electrical surges can be induced by the transient fields, the coupling between the structures, and a partial lightning current entering the cables via its grounding. Since the Lightning Protection System (LPS) is generally designed based on the worst-case scenario, a parametric study is conducted using the FDTD method to identify the configurations in which the surges in the cables interconnecting two buildings are maximized. The results are compared to the case in which the cables are grounded at the entrance to the buildings. The direct connection to the reinforcement increases the currents and shifts the resonances towards higher frequencies.