Calculations of lightning surge currents inside buildings

This paper describes the distribution of surge currents inside a building during a direct lightning strike, on the basis of numerical simulations of building wiring, various loads, and five different combinations of metal oxide varistors connected inside the building as surge arresters and suppressors. The 10/350 ps wave with a peak current of 20 kA, which is widely accepted as a simulation of current in a direct lightning strokes, is used as the source. The network inside a building is modeled as eight branch circuits, each with a different resistive, capacitive, or inductive load and each with a different length. The results of this modeling is compared with the 8/20 and 10/1000 ps standard surge test waveforms. It is shown that the surge test waveforms in ANSIDEEE C62.41 have a peak current and duration that are both too small to represent the effects of a direct lightning strike to the mains. Instead of revising 052.41 to include larger stresses for the environment inside a building, it is urged that standards specify maximum allowable values of peak surge current and rate-of-change of current inside a building. Coordinated surge arresters and suppressors should be used to keep surge currents inside a building within the specified limits.