A strategy to evaluate the impact of intermediate sources on the performance of transmission line distance protection is proposed in this study. The influence of an intermediate infeed on the sensitivity of the reach setting and the resulting tripping performance of a distance protection scheme is the main emphasis of this study. The proposed strategy considers the effectiveness of various protection schemes on the protection challenges expected on the National Grid transmission network due to future changes in the generation mix. PowerFactory (DIgSILENT PowerFactory software package) will be used to simulate a double circuit transmission network, when a fault occurs and the strength of the main and intermediate sources change from weak to typical to strong. This study discusses various solutions to the problems observed and a methodology for adapting the grading strategy of distance protection as transmission networks evolve into the future.