Experimental and theoretical investigation of the harmonic distortion in the 600v urban railways system of Athens

In this paper an experimental work regarding power quality in existing dc traction systems is presented and evaluated. The measurements were performed in two substations of the Athens-Piraeus Electric Railways (ISAP), according to the European standard EN 50160 and EN 61000, using 3 wire connection systems. The examined traction system use 600V DC. The main supply systems usually consist of a medium voltage substation feeding a rectifier which provides the dc power supply of the traction motors. The DC power supply is provided using grounded negative bus. The three-phase rectifier (controlled or uncontrolled) produces harmonics induced to the AC network. The measurements were performed in two substations one old with oil insulated transformers and old 12-pulse rectifier and in one recently refabricated with dry type transformers and new rectifier.