A distance from a measurement point to a fault in a three-phase circuit is determined. The measurement point is located at an output of a power sub-station and the three phase circuit has a loop circuit having an associated net fault line current and a ground current. A derivative of the net fault line current of the loop circuit as measured from the measurement point is calculated. An uncompensated distance to the sub-cycle fault using at least the derivative of the net fault current is determined, and configured, to compensate for the ground current of the loop circuit. The compensation is applied to the uncompensated distance to produce a compensated distance to the sub-cycle fault.