A 25Hz phase-sensitive track circuit is used inelectrified railway stations allowing determination of whether atrain occupies a track section and avoiding the interference oftraction current to signal circuit. The transmissioncharacteristics of a 25Hz phase-sensitive track circuit in theregulated state were studied, allowing the development of amodel of choke transformer and track circuit. Considering theimpedance bond, a four-terminal network model that adjusts thestate of track circuit was built, and a distributed-parametermethod was applied to solve the four-terminal networkcoefficient of the track circuit in the regulated state. Thesinusoidal steady-state responses can be obtained directly fromthe complex frequency-domain solution, and the DC steady-stateresponse can be calculated using the final value theorem ofLaplace transform theory. This steady-state analysis of trackcircuit transmission lines allows the characteristic analysis oftrack circuit during steady state operation. This work also canserve as guidance to help ensure signal transmission withoutdistortion. Finally, the transmission characteristics of the trackcircuit were simulated by Matlab. The simulation results showthat the transmission characteristics of the track circuit inregulated state is closely related to the length of the track circuitand ballast resistance.
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