This work addresses the imbalance in the literature regarding the modeling of waveform distortion resonance and propagation in low-frequency railway electrification systems, focusing on the Swedish Electric Railway Power Supply (ERPS). A framework is proposed for modeling synchronous components of waveform distortion up to 25 kHz, incorporating local interactions between traction converter stations (TCSs) and rolling stock. The nodal admittance matrix is developed for an autotransformer-fed circuit with three railway sections and four TCSs. Rolling stock is represented through a measurement-based Norton model capturing high-order components and probabilistic harmonic emissions. Monte Carlo (MC) simulations assess resonance and propagation uncertainties under variable operating conditions. Results reveal key influences of railway section lengths, filters, and stochastic emission models on impedance characteristics, offering ERPS tools for future assessment.