A method and a system for determining a circular characteristic for distance protection of a three-phase electric line (30), the system comprising means for detecting a fault (F) on the electric line (30), means for identifying a faulted phase or phases of the electric line, means for determining, at a measuring point, a first fault loop impedance by using voltage(s) of the faulted phase(s), a second fault loop impedance by using a polarization voltage and a third fault loop impedance by using predetermined line parameters, and means for determining a radius and midpoint of the circular characteristic.