This article addresses the power quality issues in railway systems. It starts with a distributed parameter approach to the determination of the current and voltage harmonics along a railway feeder. For the assessment of the harmonic distortion, three global indices for the harmonic voltage, current, and power are suggested, which take into account the spatial harmonic distribution (up to the 19th harmonic) along the entire feeder and the feeder length for all possible locomotive positions. Also, they consider the receiving-end resistance representing the power quality conditioner of the feeder's end. This is followed by a proposed technique for identifying the optimal value of this resistance, resulting in the least values of the proposed global harmonic distortion indices. It is shown that the two resistance values yielding the minima of both voltage and current harmonic indices are almost equal and are larger than the one leading to the least harmonic index for the harmonic power. A comparison of the improved harmonic conditions with the identified optimal feeder termination resistance indicates the applicability of the suggested approach.