Evaluating the risk of equipment disruption related to voltage sags

This paper presents a methodology for risk analysis applied to voltage sags in distribution networks. The basis of the methodology is presented, as well as the description of its implementation. Two evaluations are performed for a given distribution network: frequency of occurrence of voltage sags and the impact of the voltage sags on customer loads in statistical basis. Fault events are simulated using the Monte Carlo method, in which variables related to faults are determined according to their probability distributions. The magnitude and the duration of voltage sags and occurrence of interruptions are determined in the network points by considering the fault conditions and the line overcurrent protection devices characteristics. The results presented are indices of sag events and equipment breakdown for any desired voltage tolerance curves, which allows mapping the network in respect to risk, associated to sag events. The emphasis of the studies lies upon the practical questions that appear when industries already installed or planning installation are faced with decisions which are influenced by the rate of occurrence of voltage sags.