A transmission line tower model taking into account the distribution of the current along the metal structure: application of the model in predicting occurrence of the backflashover

Abstract

This Project proposes a transmission line tower model to be used for analyzing lightning overvoltages on transmission towers. The model considers the transmission tower as being a vertical transmission line. Taking into account this tower model, the currents and voltages in frequency domain will be calculated by using the Numerical Electromagnetic Code (NEC-2). Then, by using simulated currents and voltages it will be possible to calculate the tower impedance seen from the top of the transmission tower. The impedance will be approximated by a rational function that has, in time domain, an equivalent circuit representation (circuit constituted by resistances, inductances and capacitances). This equivalent circuit is the transmission tower model developed directly in time domain and it can be easily used in softwares such as Alternative Transients Program (ATP). The proposed model can be used without softwares such as ATP. In this case, the currents and voltages of the equivalent circuit before mentioned must be written as being state equations. This way, the simulations of lightning overvoltages can be evaluated by using any computational language. The main advantage of the proposed model is the fact that it takes into account the current distribution on each segment of the modeled geometry that represents the transmission tower. Therefore the developed power transmission tower model can be used to simulate more accurately electromagnetic transients during the lightning strikes on transmission towers. Therefore, taking into account the reduction of the failures in the insulators, there will be a reduction of the number of outages through the backflashovers. (AU)