This study presents an evaluation of the influence of mutual coupling modelling on the effectiveness of a distance protection scheme suitable for long parallel transmission lines. Sliding single-line-to-ground fault simulations have been carried out in MATLAB using a phase-domain approach. The output voltage and current signals were applied to the distance relaying algorithm considering exact compensation parameters. It is shown that, for the system considered, assuming parallel transmission lines modelled as a six-phase line, an average relative error of 1.19% is found for the magnitude of the apparent impedances seen by the relay.