Closed current flow during a lightning discharge

Inhalt:
The steepness of the lightning current in down conductors is crucial for the entire lightning protection system, since it may induce high voltages in open loops and lead to electric breakdown. Various methods, aiming for the reduction of the steepness, exist, where the most common one is to share the current among multiple down conductors. In this contribution an alternative approach is investigated. It makes use of the fact that during a return stroke, the electric circuit closes via displacement currents. For the suggested approach it is necessary to determine the electric fields on ground over time coming with the return stroke. To this end one assumes a flat and perfectly conducting ground, leading to an analytic description of the electric fields. Numerical results affirm the supposition that the circuit closes via the displacement current. The setup of proposed approach is sketched and eventually its effectiveness is demonstrated on an example.