New circuital models of grounding systems and PDS for EMI analysis during a lightning strike

In this paper circuital models of a power drive system (PDS) and of grounding systems are proposed in order to analyse electromagnetic interferences (EMI) induced in a PDS when a lightning current flows in the grounding system. The models have been developed adopting the network approach with lumped parameters and have been implemented using the software Matlab. A high frequency (HE) model suitable to simulate the impulse response of a PDS is described and a generalized method in order to calculate the lumped parameters values of grounding system models is presented. The new method takes into account the burial depth of electrodes as regards their length. The validation results of this new method are presented. It has been made comparing simulation results with the ones obtained with the more rigorous models developed by Yaqing Liu et al. and by Grcev respectively, the transmission line method (TLM) and electromagnetic field method. The grounding systems developed circuital models are simpler than those realized with the TLM and the electromagnetic field methods, they require a shorter computational time and a minor cost because an on sale software for network simulation can be used. These characteristics permit to combine the grounding system model with the PDS HF circuital model, obtaining an only model that permits to analyse EMI generated in every section of the drive during a lightning strike giving only the waveform of the lightning current in time domain, as input of the model.