Abstacts The main protection provided for power transmission lines against short circuits is distance protection. The performance of distance relays is affected by fault resistance and zero mutual coupling of parallel transmission lines. These factors may cause overreach or underreach in distance relays. Different protective algorithms have been proposed to eliminate these effects. The aim of this research is to evaluate the performance of the proposed algorithms using healthy and faulted line currents or estimated healthy line currents based on faulted line currents. The investigation covers various fault conditions in view of speed and accuracy. Then the speed and accuracy of some of these algorithms are improved using some modifications. Finally a new algorithm based on estimation of angle of the impedance deviation (difference between actual impedance and measured impedance) is presented. This algorithm can eliminate impact of zero mutual coupling or fault resistance on the measured impedance by a distance relay. Furthermore, the impacts of fault resistance and zero mutual coupling can be eliminated simultaneously using this algorithm. In order to demonstrate the performance of protective algorithms, two appropriate power system models have been simulated in PSCAD/EMTDC.