A Simulation Model of Audio-Frequency Track Circuits

The new high speed railway lines, under construction in Italy, are electrified in 2x25 kHz – 50 Hz and adopt a signalling system with audio frequency track circuits (ranging from 2.1 kHz to 16.5 kHz). Although the choice of audio range is due to the necessity of avoiding interference problems between traction and signalling system, traction current presents a harmonic spectrum, due to the control systems, that can be cause of disturbances to track circuits operation with a possible impact on transportation regularity. With the aim of system availability assessment it becomes very important to develop reliable and robust models of the traction and signalling system. The paper illustrates a model adopted to simulate the audio frequency track circuits and implemented in Alternative Transient Program (ATP). The main results obtained are presented with the model validation, realized through a measurement campaign performed on the new railway line Rome-Naples, and with a sensitivity analysis of the same model.