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Abstract
The energy efficiency of transportation is a crucial point for the rail and metro system today. The optimized recovery of the energy provided by the electrical braking can lead to savings of about 10% to 30%. Such figures can be reached by infrastructure measures which allow the recovery of the breaking energy that is not directly consumed by the rail system and dissipated in rheostat resistors. A methodology for the accurate estimate of such energy is valuable for a reliable evaluation of the cost–benefit ratio associated with the infrastructural investment. The energy can be estimated by measuring a braking current flowing in the rheostats. The varying duty-cycle associated with the high dynamic variation, from zero to thousands of amperes, makes the current measurement very challenging. Moreover, the digitization of such waveforms introduces systematic errors that affect the energy estimation. To overcome these issues, this paper proposes a technique to measure the power and energy dissipated by the rheostat of a DC operated train with high accuracy. By means of an accurate model of the electrical braking circuit (chopper and rheostat) and the frequency characterization of the current transducer, a correction coefficient as a function of the duty-cycle is estimated. The method is then applied to data recorded during a measurement campaign performed on-board a 1.5 kV train of Metro de Madrid during normal operation. Using the proposed technique, the estimation of the dissipated braking energy is improved by 20%.
Highlights
Regenerative braking is widely used since the dawn of electrical railway traction
Fit function that approximates frequency dependence.AAcomparison comparisonbetween between the the actual actual current current flowing through the rheostat and the distortion introduced by the current sensor and the flowing through the rheostat and the distortion introduced by the current sensor and the subsequent subsequent digitization is provided
Provided.behavior of the correction factors as a function the digitization is thethe behavior of the correction factors as a function of theof dutyduty-cycle are described, including a description the uncertainty introduced the initial cycle are described, including a description of the of uncertainty introduced by theby initial phase phase of the of the sampling procedure that is considered as stochastic information
Summary
Regenerative braking is widely used since the dawn of electrical railway traction. All breaking energy produced by the traction motors during the braking stage was dissipated by rheostats placed on-board rolling stock. Locomotives have an intelligent system able to direct the braking energy flow towards the overhead contact line if other nearby trains can collect such energy, or towards the braking rheostat to be transformed into heat. The flat-rate scheme of energy billing, adopted for railway undertakings and used until recently, made the knowledge of the energy dissipated by the braking rheostats marginal. Imposes billing to be performed on real rolling stock energy consumption. This choice will foster energy saving and will transform the railway system in a more sustainable means of transport
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