A First Approach on the Fault Impedance Impact on Voltage Sags Studies

Abstract

An analysis of the fault impedance impact on studies of voltage sags caused by system faults is presented. The simulation of 62 case studies of phase-to-ground faults on 13.8, 69, 138 and 230 kV transmission lines were performed and the voltage of a 380 V sensitive industrial busbar consumer was monitored. These lines are part of the electrical system of the city of Goiania, Brazil. For each case study, different fault positions were simulated by considering resistive fault impedances of 0, 2, 5, 10, 15 Ω or a random fault impedance with a specific distribution function. Long-term simulation scenarios were obtained by the Monte Carlo method and analyzed based on their cumulative distribution functions and probability density curves of voltage sags. This is one major contribution of this work. We found that, the greater the fault impedance, the smaller the average number of voltage sags expected per year at the end-user busbar. However, the behavior of the average number of voltage sags of a given class of magnitude with the fault impedance does not follow a general law.