Harmonic Impedance Studies of Swedish Railway Power System Using Wide-Area Modeling Approach
This paper presents a comprehensive framework for wide-area modeling and harmonic resonance assessment in the AC single-phase Swedish electric railway power system (ERPS). The methodology integrates the modeling of key elements of the catenary system, such as synchronous generators, transmission lines, transformers, and filters, while addressing the dynamic behavior of rolling stocks and inherent system uncertainties. Study cases, including Monte Carlo simulations, are developed to evaluate probabilistic scenarios and impedance variations across the network using nodal admittance modeling and frequency scanning. Key contributions include a method to model moving loads, a comprehensive approach to harmonic resonance analysis based on meshed grid characteristics of the ERPS, and an uncertainty assessment framework that highlights insights for system planning and mitigation actions. Results indicate that filters installed at traction converter stations (TCS) introduce resonances typically between the 10th and 25th harmonics, with amplification factors exceeding five times at certain locations. The wide-area modeling approach is essential due to continuous power supply and influence of distant network sections. Uncertainties related to moving loads, number of rolling stock units, and remote system areas cause variations in both frequency and magnitude of series and parallel resonances. Monte Carlo simulations effectively capture these variations, providing probabilistic information for resonance frequency location and impedance variation. The findings offer critical insights for system planning and mitigation actions in ERPS.