At the moment, I study something about audio-frequency track circuits for railway applications and to understand its operation, an accurate model of such a circuit is required.
The circuit of audio-frequency track circuits uses the actual railway track as a conductor to let the current flow through. Also, since the normal length of track circuits can be in a range of 400 m to 2 km, these tracks may be treated as transmission lines.
Normally, transmission lines can be modeled as lumped or distributed parameters, which contain series impedance (i.e. resistance and inductance) and shunt admittance (i.e. conductance and capacitance).
I would like to know whether this range of frequency (i.e. 1kHz - 20kHz) will have any effects on these parameters? As I know it will definitely affect the resistance due to the "skin effect", but I do not know about the others.