Adaptive Zero-Sequence Overcurrent Criterion for Earth Fault Detection for Fault Current Passage Indicators in Resistor Grounded Medium Voltage Networks

Abstract

Earth faults are the most common disturbances in medium voltage networks. They cause threats to equipment and people, and reduce the quality and reliability of electricity supply. Detection and localization of earth faults is a key challenge to network operators, therefore it is important to constantly develop criteria that allow for an unequivocal assessment of the current network state. This article focuses analysis of effectiveness of classic zero-sequence overcurrent criterion and on modification of the zero-sequence overcurrent criterion applied in fault current passage indicators, which are the devices used to effectively detect and locate earth faults. Two new adaptation criteria for networks with resistor grounded neutral point have been proposed, which enable significant improvement of the effectiveness of earth faults detection, in particular high impedance ones. The effectiveness of the criteria was verified computationally and in simulations. In certain situations, the proposed solutions may be over 40% more effective than the classic criterion. The value of detected transition resistance $R_{F} $ also increases significantly. All the above-mentioned advantages make their potential use in practice very beneficial.