Research on the modeling of the impedance match bond at station track circuit in Chinese high-speed railway

Frequency-shift keying audio jointless track circuit is used in high-speed railway in China. However, within the station, track circuit with mechanical insulation is applied. In complex circuit network of electrified railway station, impedance match bond is designed to ensure the normal operation of the track circuit and the protection of strong traction current interference. As a combination of strong and weak electricity components of track circuit, impedance match bond is both the part of the loop of the traction current and the part of the transmission line of track circuit, playing a very critical role in the electrified railway. The structure of impedance match bond is more complex than traditional impedance transformer, including the transformer with larger air-gap, LC resonance circuit for power frequency filtering, and components to enhance the signal frequency. Modeling on impedance match bond and study about the four-terminal network parameters of impedance match bond are in favor of the following two aspects: modeling of the overall traction current and calculation of track circuit working condition. By applying the transformer equivalent circuit model and combination of testing and calculation, the accurate model of impedance match bond is constructed and verified. Finally, for ease of track circuit calculation, four-terminal network model of impedance match bond under different signal carrier frequencies is presented