Earth Fault Protection Selectivity Issues on Reactance Earthed Distribution System

Increase in power demand, green initiatives and regulatory requirements force system operators to adopt more complicated distribution system layout which are resulted in dissension from traditional distribution system practises. The main source of this complexity can be listed as; extensive application of embedded generation into distribution systems, different earthing practices, increasing percentage of under-ground cables and lastly, parallel feeders causing loop flows. One of the consequences of the increased complexity is malfunctioning in the protection systems namely; false tripping especially for the earth faults. Thus, conventional non-directional protection relays are, grad-ually, replaced with the directional ones in radial topology. How-ever, directional protection is more expensive since requirement of additional measurement devices is imminent. Consequently, to facilitate cost effective protection system implementation, directional protection and non-directional protection performances should be investigated properly. Distribution system which earthed trough reactance may also suffer directional discrimination because of possibility of unintentional resonance between neutral reactor and cable capacitances. In this study, boundaries of directional and non-directional protections are investigated by taking into account neutral reactance, cable length and parallel feeder number. It is proposed that, a hybrid algorithm selection procedures based on system parameters should be undertaken for a successful and selective protection.