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Determination of Overcurrent Protection Settings Based on Estimation of Short-Circuit Currents Using Local Measurements

Abstract:

On Electrical Distribution Systems (EDSs), system changes upstream of overcurrent protective devices result in variations of the Thevenin equivalent and consequently in variations of short-circuit currents (Icc). Changes in the Thevenin equivalent are caused by some operating condition or by growth of transmission system. In that condition, the fixed settings in overcurrent protection could cause selectivity problems in the protection systems. This paper proposes the development of an overcurrent protection scheme. The main idea is to change the settings based on the Icc of EDS. By adaptivelychanging settings allows mitigation of possible miscoordinations caused by Icc variation effects. The IEC 60909 standard is used to calculate the Icc, by using a prefault Thevenin equivalent, wich is obtained by the voltage and current measurements acquired at the relay location. The proposed methodology is developed on PowerFactory - DIgSILENT software and applied to the IEEE Distribution 13-Bus Test Feeder System.