A digital distance relay is provided with voltage and current signals from one end only of the protected circuit, and is expected to assess the fault location on the basis of these locally derived signals. Many parameter of the power system exert an important influence on the calculation of fault impedances and fault location. An important aspect of designing a distance protection scheme is to select correct values of voltages and currents at relay location so that the calculated impedance during a fault condition is the positive-sequence impedance from the relay location up to the fault location.In power systems including double-circuit transmission lines (phases R1, S1, T1 - R2, S2, T2), the possibility of intersystem faults is given. Common distance relays are not always able to detect the fault, because the impedances are very complicated. The paper presented demonstrates how a suitable combination of voltages and currents leads to impedances for the faulted phases, which do not differ from the impedances seen by the three-phase fault. The unsymmetrical faults phase Rl to phase R2 to earth, phase S1 to phase T2, and phase S1 to phase T2 to earth are discussed. The impedances seen by the relays including the healthy phases are also discussed. For the calculation the zero-sequence mutual coupling of the double-circuit line and resistances at the fault location are taken into account.