Effectively Determine Confidence Intervals of Bus Voltages Served for Setting Overcurrent Relays in Distribution Networks

In distribution networks, either nominal bus-voltage values or voltage values calculated right after some pre-determined cycles are mostly used as reference voltages for power-flow and fault-current analysis. The use of nominal bus-voltage values could lead to inaccurate calculations of power flows and fault currents in the distribution network (DN), which can result in the protection mis-coordination. Moreover, the analysis of power flows and fault currents is continuously repeated by the updated bus-voltage values, which could be not necessary and complicated to settings of overcurrent relays (OCRs). Therefore, this paper will propose a novel statistical data-filtering method to determine confidence intervals of bus voltages in a distribution network for effectively self-adjusting pickup and tripping thresholds of overcurrent relays without periodic calculations of fault parameters. In case of not having any change in DN topologies, selection of the best confidence intervals of bus voltages can minimize the repeated calculations of power flows as well as fault currents, meanwhile ensure the reliable operation of OC relays in the distribution network. In addition, the proposed data-filtering method of bus voltages is also compared to other methods, e.g. Kalman filter-KF, Density-Based Spatial Clustering of Applications with Noise-DBSCAN, Discrete Wavelet Transform-DWT, and Singular Spectrum Analysis-SSA. Simulation results of a protection system of 22kV DN are presented to validate the effective setting of pickup and tripping thresholds of overcurrent relays through the most confidence intervals of bus voltages determined.