Abstract
Harmonic resonances are part of the power quality (PQ) problems of electrified railways and have serious consequences for the continuity of service and integrity of components in terms of overvoltage stress. The interaction between traction power stations (TPSs) and trains that causes line resonances is briefly reviewed, showing the dependence on infrastructure conditions. The objective is monitoring of resonance conditions at the onboard pantograph interface, which is new with respect to the approaches proposed in the literature and is equally applicable to TPS terminals. Voltage and current spectra, and derived impedance and power spectra, are analyzed, proposing a compact and efficient method based on short-time Fourier transform that is suitable for real-time implementation, possibly with the hardware available onboard for energy metering and harmonic interference monitoring. The methods are tested by sweeping long recordings taken at some European railways, covering cases of longer and shorter supply sections, with a range of resonance frequencies of about one decade. They give insight into the spectral behavior of resonances, their dependency on position and change over time, and the criteria needed to recognize genuine infrastructure resonances from rolling stock emissions.
Highlights
Railways are being used worldwide as an efficient and effective transportation infrastructure for people and goods, both long distance and within an urban context
The traction supply arrangement differs from three-phase industrial networks in several aspects: AC railways are single phase operated at the medium voltage (MV) level, they have a physical extension typical of a transmission network but separated into smaller sections for most AC railways, the traction line feeds power to distributed moving loads, and the interaction between traction power stations (TPSs) and trains causes a variety of power quality (PQ) phenomena that are relevant to internal operation and disturbance to third parties [1]
As shown in [9], the system may be analyzed by means of multiconductor transmission line (MTL) equations, representing the overall network as a meshed set of series and parallel connected branches, to which lumped circuits may be attached at nodes
Summary
Railways are being used worldwide as an efficient and effective transportation infrastructure for people and goods, both long distance and within an urban context. The hot path, concerns mainly the traction supply and overhead distribution system with an overall return along the return circuit and earth; the studied circuit is relevant for distortion shared by the TPSs and trains, and propagated back onto the high voltage feeding line and into the public grid. The interpretation given in [9], it may be said that LFOs are related to system instability [23], mostly caused by delay and phase rotation along the line [24] and interaction of active controls onboard rolling stock, applying power factor compensation [25,26] This led to the catastrophic blackout of the Swiss network in April 1995 (as reported in [25,27]) and significant research activity among the infrastructure owners, manufacturers, and scholars. The work is structured as follows: Section 2 describes the quantities and conditions for resonance to occur; Section 3 goes into the details of the detection and interpretation of harmonic resonances; Section 4 reports the results obtained from measured data collected during test runs in Switzerland and France, covering both 16.7 Hz and 50 Hz traction supply systems
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