Directional Fault Detection Based on Active Power Coefficient in Resonant-Earthed Distribution System

Transients-based earth fault protections cannot trip reliably for earthing faults with high resistance in a small current distribution system due to low magnitude of the high-frequency transient signals. Directional protection based on zero-sequence active power can trip reliably only with the presence of damping resistor during fault, and can be used as back-up protection. Phase comparison method is not applicable to arcing fault and intermittent fault. Energy method also has a drawback because of its vulnerability to current transformer error. This method which use the active power coefficient of the zero-sequence signal which is lower than 100 Hz is proposed. This method determines the faulty point direction through this coefficient. Digital simulation and actual fault recordings data have verified the feasibility of the proposed method, and is not subject to measurement error of current transformer.