System and method for determining location of phase-to-earth fault

A system for determining a distance of a phase-to-earth fault on a three-phase electric line of an electric network, the system comprising:

• means for monitoring current and voltage quantities of the three-phase electric line at a measuring point;
• means for detecting a phase-to-earth fault on the three-phase electric line;
• means for identifying a faulted phase of the three-phase electric line;
• means for determining a first estimate value for a distance between the measuring point and a point of fault on the basis of values of the monitored current and voltage quantities and a first equation which relates the current and voltage quantities to the distance and is based on a fault loop model of the electric line, in which model the load of the electric line is located between the measuring point and the point of fault;
• means for determining a second estimate value for the distance between the measuring point and the point of fault on the basis of values of the monitored current and voltage quantities and a second equation which relates the current and voltage quantities to the distance and is based on a fault loop model of the electric line, in which model the point of fault is located between the measuring point and load of the electric line;
• and
• means for selecting, according to predetermined criteria, one of the determined two estimate values as the distance between the measuring point and the point of fault.

An apparatus for determining a distance of a phase-to-earth fault on a three-phase electric line of an electric network, the apparatus being configured to:

• monitor current and voltage quantities of the three-phase electric line at a measuring point;
• wherein the apparatus is further configured to, in response to receiving an indication of a fault on the three-phase electric line and of a faulted phase of the three-phase electric line:
• determine a first estimate value for a distance between the measuring point and a point of fault on the basis of values of the monitored current and voltage quantities and a first equation which relates the current and voltage quantities to the distance and is based on a fault loop model of the electric line, in which model the load of the electric line is located between the measuring point and the point of fault;
• determine a second estimate value for the distance between the measuring point and the point of fault on the basis of values of the monitored current and voltage quantities and a second equation which relates the current and voltage quantities to the distance and is based on a fault loop model of the electric line, in which model the point of fault is located between the measuring point and load of the electric line;
• and
• select, according to predetermined criteria, one of the determined two estimate values as the distance between the measuring point and the point of fault.