Patent ID: 8717036

Claim:
A method for detecting a phase-to-earth fault on a three-phase electric line of an electric network, the method comprising: monitoring a zero sequence current on the three-phase electric line and a zero sequence voltage in the electric network; detecting an earth fault in the electric network based on a value of the zero sequence voltage; determining a difference between a first zero sequence current monitored before the earth fault and a second zero sequence current monitored during the earth fault; determining a difference between a first zero sequence voltage value monitored before the earth fault and a second zero sequence voltage value monitored during the earth fault; determining a neutral admittance, based on a ratio between the difference between the first and second zero sequence currents and the difference between the first and second zero sequence voltages; and comparing the determined neutral admittance, to a predetermined operation characteristic to detect a phase-to-earth fault on the three-phase electric line, wherein the predetermined operation characteristic, when presented on an admittance plane, defines a closed area such that the center of the closed area is offset from the origin of the admittance plane towards a negative susceptance direction and/or towards a negative conductance direction.