Analysis of the origin of measured voltage sags in interconnected networks

This paper deals with the assessment of the origin of voltage sags due to faults in real, interconnectednetworks. The first step in regulating such faults is to determine the origins of measured voltage sags.Thus, the challenge of this study was to use only the main measurements associated with voltage sags,i.e., the residual voltage, the time the voltage sags occurred, and their duration to detect their origins. Nocorrelations with data from the existing protection systems were used because they were not available.Different operators who do not exchange any data with each other manage the interconnected networksthat we considered, and this increased the complexity of the study.In this paper, we analysed the main aspects of the propagation of voltage sags in interconnectednetworks, and we focused our attention on High Voltage (HV) and Medium Voltage (MV) systems inter-connected by HV/MV stations. Two methods were used to determine where the voltage sags originated inthe network, and the methods used only the measurements associated with the voltage sags. Both meth-ods were used to evaluate the huge number of measured voltage sags that occurred in an MV distributionsystem over a period of one year. These two methods: are presented after a brief review of the theoret-ical methods for simulating the propagation of voltage sags among the nodes of an electrical network.This review is valuable for defining the rules associated with each method. The paper contributes to theliterature by providing analyses of a huge number of voltage sags measured in interconnected systems.The main outcomes show that it is possible to detect the origin of the sags using the main measurementsof the voltage during the fault only on the MV side of the transformers that are installed in the HV/MVstations. The statistical analysis of these measurements allowed us to classify the origins of the sags betterthan imposing any conditions on the value of the residual voltages of the sags. Conversely, the origin ofthe sags in the HV network can be identified better if limits are assigned to the residual voltages.