Rail transport in Poland uses direct current electric traction to power vehicles (locomotives and multiple units). It is therefore necessary to convert the AC voltage of the power system into the DC voltage of the traction system. The conversion of alternating voltage into direct voltage takes place in traction substations. Rectifier units installed at traction substations are used for this purpose. As a result, electric traction should be classified as non-linear consumers. In addition, the traction substation load changes dynamically. All this makes the electric traction a recipient generating a number of disturbances to the network. These disturbances affect the quality of electricity in the power system from which the traction substations are supplied, and the quality of energy in auxiliary and non-traction lines. The article presents the results of the analysis of measurements of electricity quality indicators recorded at selected points of the traction substation line. Parameters characterizing the quality of electricity were recorded, among others, in in the main line supplying the traction substation, non-traction needs line and auxiliary circuits. The presented article is another in a series of publications related to the assessment of the impact of DC electric traction on the power system.