Attenuation by a lightning protection system of induced voltages due to direct strikes to a building

This paper deals with induced transient voltages on electric circuits inside a protected building due to direct lightning strikes. The prediction of these overvoltages is a mandatory requirement for every EMC design of the installations inside the stricken building. The maximum level of expected transients and the efficiency of their attenuation by different configurations of a lightning protection system (LPS) are evaluated by a new simplified approach. The results are compared with those obtained by a complete circuit prediction model. A loop transfer impedance is defined as the ratio between the open end voltage induced in metal loops and the injected lightning current. This impedance is used to set the upper and lower bounds of the frequency spectra of the voltages induced in the loops internal to the building. The results are helpful in locating critical positions of circuits and devices within the volume protected by a LPS.