Back Up Protection Scheme for High Impedance Faults Detection in Transmission Systems Based on Synchrophasor Measurements

High impedance faults are rather difficult to detect, due to their inherent characteristics. However, in most cases high-impedance low-current faults evolve to low-impedance high-current faults, thus giving rise to life hazard situations and equipment damage. In this article, a novel back up protection scheme for high impedance fault detection, based on synchrophasor measurement technology, is proposed. In fact, the presented detection method can be thought as the combination of a classic differential and a classic admittance relay. The protection device designated for high impedance fault detection, incorporating the proposed novel protection algorithm, permanently monitors transmission line's shunt admittance thus being able to detect changes-increase in the resistive part of shunt admittance, namely the shunt conductance. Actually, a sudden rise of transmission line's shunt conductance is a strong indicator of high impedance fault inception. Conducted computer simulations confirmed a high degree of selectivity and sensitivity of the proposed method. Moreover, the technical feasibility of the approach was tested considering real-world measurement data obtained for two 220 kV transmission lines. From the acquired data, measurement uncertainties of the monitored parameters in normal operating conditions, were calculated. The results demonstrate excellent sensitivity of the proposed method, even for the case of short transmission lines during low-loading conditions.