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Electrified railways are one of the most powerful wide frequency range sources of disturbances that interference on signaling and radio communication systems. This is especially true for new types of vehicles equipped with electronic static converters with pulse width modulation (PWM), which highfrequency interferences in rails can have frequencies up to several tens of kHz. The electrical disturbances from vehicles (trains, locomotives) propagate through traction network [1]. There are five feeding systems that can be used with an AC electric railway. : the direct feeding system, the direct feeding system with return wire, the booster trans-former feeding system, the autotransformer feeding system and the coaxial cable feeding system [2, 3]. In general, the traction network are composed of the overhead supply conductors and traction rails electrically connected to earth or (and) with additional earth potential conductors. The return current from rolling stock axles flows in rails back to the supply substation. Therefore rails act as a path for electrical disturbance propagation. To ensure the electromagnetic compatibility (EMC) of new types of rolling stock with signaling and radio communication systems, they are subjected to an acceptance procedure that includes on EMC tests in accordance with European and national regulatory standards and norms [1, 4]. But under some unfavorable operation conditions for the trains that were successfully tested and are in operation with old vehicles on the same lines (sometimes with old feeding system), the disturbing current generated by vehicles may reach values greater than the allowed values [4, 5]. As such unfavorable operational conditions may be considered increasing number of trains, low distance between track circuit receiver and vehicles or supply substation, low rail-to-earth conductivity and conductivity of earth. To proof the electromagnetic compatibility (EMC) between rolling stock and signalling systems it is need accurate modeling of the test cases with taking into account particular operation conditions [1]. The models for the distribution of the traction return current in the direct feeding AC and DC electric railways have been described in many works (see for example [2]). The multiconductor transmission line (MTL) approach has been successfully used in [6, 7] to investigate the electromagnetic processes in Auto Transformer (AT) electric traction systems for high speed railways. The distribution of the traction return current harmonics in rails and their influence on track circuits have been modeled in [8,9]. To describe various traction feeding networks in a uniform way the chain circuit model was used in [3]. Harmonic power flow in traction network was analyzed in [10]. The aim of the work is to establish mathematical and computer model for distribution of traction current harmonics in AC direct feeding traction network with multiple vehicles in feeder zone. This model is an evolution and simplification of models represented earlier [8]. The work has been performed in order to proof the electromagnetic compatibility of new trains equipped with electronic static convert-

Modeling of the traction current harmonics distribution in rails