Patent ID: 7999557

Claim:
A method for determining a location of a phase-to-earth fault on a three-phase electric line of an electric network, the method comprising: monitoring current and voltage quantities of the three-phase electric line at a measuring point; determining, after a fault occurs in the three-phase electric line and when the ratio of a fault current and load current has a first value, a first fault distance line which indicates an estimate of the distance of the fault from the measuring point in relation to an equivalent load distance on the basis of values of the monitored current and voltage quantities and an equation which relates the monitored current and voltage quantities to the fault distance, wherein the equivalent load distance indicates a distance of an equivalent load point from the measuring point which equivalent load point equals to a total load of the electric line modelled to be concentrated in a single point of the electric line; determining, when the ratio of the fault current and load current has a second value which differs from the first value, at least one second fault distance line which indicates an estimate of the distance of the fault from the measuring point in relation to the equivalent load distance on the basis of values of the monitored current and voltage quantities and an equation which relates the monitored current and voltage quantities to the fault distance; determining a distance or distances from the measuring point at which the determined fault distance lines intersect when superimposed; and determining the distance between the measuring point and the point of fault on the basis of the determined distance or distances of intersection.