Energy Saving Potentials in Railway Operations under Systemic Perspectives
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Date
2019-06
Publication Type
Doctoral Thesis
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Abstract
This thesis deals with the comprehensive topic of energy saving in railway operations. In contrast to prevailing literature, it focuses on systemic aspects and interactions, given the research question “which energy-oriented optimisations in subsystems show positive effects considering the entire railway system—and which additional saving potentials disclose by holistic analysis?”
To approach this question, a more comprehensive system understanding has to be gained. Due to the high degree of complexity, a closed analytic system description is not possible. Thus, based on literature and some data, the—to the author’s best knowledge—first model describing the entire energy chain from primary energy to wheel—connecting the domains of energy generation, energy transmission, operational decisions, vehicle driving dynamics, and drive chain—is developed. The model is built hierarchically, consisting of the five major subsystems vehicle, energy supply, track, operation control, and the environment, which are themselves built up from sub-subsystems.
Naturally, a that comprehensive model requires some simplifications in order to keep the scope manageable. While the driving dynamics—as core domain of railway operations—are described quite precisely, especially in energy transmission and drive chain modelling, significant simplifications are applied. For the prior, a constant catenary voltage is used to determine catenary current and losses, which is valid for 15 kV, 16.7 Hz and, with some limitations, for 25 kV, 50 Hz systems—but not for DC systems, in which the catenary voltage is strongly depending on the actual operational situation. Also, the description of the drive chain as cascade of efficiencies is limited in precision—however, electro-magneto-mechanical models are required for a higher degree of precision, not being feasible for a first approach to a model of the entire system.
Altogether, the definition and implementation of this comprehensive model is successful, fulfilling a task that prior projects—as Railenergy—formulated as goal, but did not reach it.
Possible approaches to energy saving are then collected from literature as first source. Thereby, the number of available publications found on this topic is that large that a complete review and treatment is impossible—which results in an expansive but not comprehensive study presented in this thesis. Additionally, the developed system model is analysed in order to understand systemic interrelations and identify possible additional saving potentials.
Based on these results, the approaches of including environmental influences in operational decisions, synchronising braking and acceleration phases, and different applications of energy storage systems and supply system modifications are tested in case studies.
In the end, it is found that subsystem optimisations show a positive effect on primary energy level as long as they are properly engineered—i.e., as long as no side-effects of the measure’s implementation reduce or even annihilate the optimisation effect (e.g., additional weight vs. increased efficiency). In terms of systemic potentials, only few promising approaches are found; the most important measure in a systemic context proved to be the interconnection of electric supply systems. Then, especially regenerated braking energy can be used to a higher degree, but also transmission distances can be lowered, thus reducing losses. As this is intrinsically fulfilled in (most) AC systems, this study—which focuses on 15 kV, 16.7 Hz systems—discloses significantly lower saving potentials as most of the literature, which focuses on DC metro systems that are typically fed unidirectionally.
Additionally, it is found that the most suitable measure strongly depends on the actual situation, comprising the general technical-operational characteristic of the system (AC, DC; long-distance, commuter, ...) but also the specific implementation. Consequently, the future of research on energy saving in railway operations is mainly seen in applied research.
Moreover, it has to be kept in mind that energy saving might conflict with other relevant aspects influencing the system’s attractiveness for its users, as time of travel or connecting services. Thus, a subtle balance between all stakeholders’ interests has to be found for each individual case.
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published
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Editor
Contributors
Examiner : Weidmann, Ulrich
Examiner : Stephan, Arnd
Book title
Journal / series
Volume
185
Pages / Article No.
Publisher
Institut für Verkehrsplanung und Transportsysteme (IVT), ETH Zürich
Event
Edition / version
Methods
Software
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Date collected
Date created
Subject
Railway; Railways; Energy Saving; Systemic Perspective; Railway Operations
Organisational unit
03674 - Weidmann, Ulrich / Weidmann, Ulrich
02610 - Inst. f. Verkehrspl. u. Transportsyst. / Inst. Transport Planning and Systems
02655 - Netzwerk Stadt u. Landschaft ARCH u BAUG / Network City and Landscape ARCH and BAUG
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