A CALCULATION METHOD OF BUS-VOLTAGE CONFIDENCE INTERVALS PROPOSED FOR THRESHOLD SETTINGS OF OVERCURRENT RELAYS ON DISTRIBUTION NETWORKS

Abstract

In a distribution network (DN), overcurrent protection relays play an important role in preventing distribution components from damages caused by high fault currents. In order to determine setting thresholds of overcurrent relays, fault analysis is implemented with various fault types, e.g. symmetrical and unsymetrical faults, by applying the nominal bus-voltage value or the bus-voltage value taken from the latest power-flow analysis results. However, the use of these values can lead to the computational inaccuracy of fault currents and a decrease in selectivity of overcurrent relays, which can cause protection mis-coordination. In addition, the continuously repeatable computation of power flows and fault currents could be unnecessary and complicated for updating bus-voltage values and setting overcurrent relays in the DN. Nevertheless, this paper will propose a novel method of statistical data-filtering in order to determine bus-voltage confidence intervals (BVCIs), which is to serve for effectively adjusting the setting thresholds of OCPRs in the distribution network. In case of not having changes in the DN topology, the proper selection of BVCIs can minimize the repeated calculations of fault currents and meanwhile ensure the reliability of OCPRs in the distribution network. Moreover, the proposed data filtering method of bus-voltages will be compared with other existing data-filtering methods like Kalman filter (KF), Density-Based Spatial Clustering of Applications with Noise (DBSCAN), Discrete Wavelet Transform (DWT), and Single Spectrum Analysis (SSA). Simulation results of 22kV distribution network protection system are used to validate the setting thresholds of OCPRs with the determined BVCIs.