An Audio Frequency Model of a 2x25 kV Traction Line for High Speed Railway Systems

The new Italian high-speed railway lines are characterised by a 2x25 kV – 50 Hz electrification standard. Train operation is carried out by the innovative ERTMS level II signalling system that is supported by audio frequency track circuits (AF-TC). The choice of the audio frequency is due to the necessity of eliminating the interference problems between 50 Hz traction currents and track circuit operation. The paper illustrates the audio frequency models, implemented in Alternative Transient Program (ATP), of both the electrification system and the track circuits. Interferences between traction harmonic currents and track circuit operation, compromising the system availability degree and the transportation regularity, are here analysed. The main results, concerning system resonance frequencies and rail current distribution, are presented and discussed.