Algorithm for identifying short circuits and overloads in medium voltage lines

Detecting disturbances in Medium Voltage (MV) lines using classical overcurrent criteria does not always ensure adequate sensitivity and selectivity. One reason for this is the decreasing distance between protection points, driven by network automation and the widespread integration of distributed generation, such as solar or wind energy sources. This article proposes an algorithm for determining the conditions for distinguishing between short circuit and overloads in overcurrent protection systems. The idea is based on measuring impedance values, specifically the rate of their changes. A key research challenge and a critical element of the algorithm is determining the appropriate time window for calculating the average RMS current within the time setting of the delayed overcurrent protection function. Simulations were conducted using the CMC 356 protection tester and RelaySimTest tool for a selected network model, protection schemes, and representative network phenomena. The goal of the article is to develop criteria for distinguishing between short circuit and temporary operational overloads.