42 research outputs found
Various Aspects and Analysis of Earthing/Grounding System for Protective and Functional Applications
Earthing or grounding means connection of neutral point or body / enclosure of a system with the ground mass to avoid any accident & smooth functioning of system whether it may be power system, fuel pipelines, telecomm, lightning protection or data processing centres. It will transfer the undesired charge directly to the ground because impedance of such path will be very low. Earthing/Grounding is low impedance return path to fault currents. Earthing should provide at generating station/ESS (Electrical Sub Stations) & consumer’s premises as required. Presented paper is focussing on earthing essential, systems, design calculations, standard practices & applications. Keywords: Types of Systems/Electrodes, Installation, Fault/size calculations, Testing, Applications
Decision-Making for Utility Scale Photovoltaic Systems: Probabilistic Risk Assessment Models for Corrosion of Structural Elements and a Material Selection Approach for Polymeric Components
abstract: The solar energy sector has been growing rapidly over the past decade. Growth in renewable electricity generation using photovoltaic (PV) systems is accompanied by an increased awareness of the fault conditions developing during the operational lifetime of these systems. While the annual energy losses caused by faults in PV systems could reach up to 18.9% of their total capacity, emerging technologies and models are driving for greater efficiency to assure the reliability of a product under its actual application. The objectives of this dissertation consist of (1) reviewing the state of the art and practice of prognostics and health management for the Direct Current (DC) side of photovoltaic systems; (2) assessing the corrosion of the driven posts supporting PV structures in utility scale plants; and (3) assessing the probabilistic risk associated with the failure of polymeric materials that are used in tracker and fixed tilt systems.
As photovoltaic systems age under relatively harsh and changing environmental conditions, several potential fault conditions can develop during the operational lifetime including corrosion of supporting structures and failures of polymeric materials. The ability to accurately predict the remaining useful life of photovoltaic systems is critical for plants ‘continuous operation. This research contributes to the body of knowledge of PV systems reliability by: (1) developing a meta-model of the expected service life of mounting structures; (2) creating decision frameworks and tools to support practitioners in mitigating risks; (3) and supporting material selection for fielded and future photovoltaic systems. The newly developed frameworks were validated by a global solar company.Dissertation/ThesisDoctoral Dissertation Civil and Environmental Engineering 201
Ab-Initio and Molecular Dynamics Simulations Capturing the Thermodynamic, Kinetics, and Thermomechanical Behavior of Galvanized Low-Alloy Steel
A seven-element Modified Embedded Atom Method (MEAM) potential comprising Fe, Mn, Si, C, Al, Zn, and O is developed by employing a hierarchical multiscale modeling paradigm to simulate low-alloy steels, inhibition layer, and galvanized coatings. Experimental information alongside first-principles calculations based on Density Functional Theory served as calibration data to upscale and develop the MEAM potential. For calibrating the single element potentials, the cohesive energy, lattice parameters, elastic constants, and vacancy and interstitial formation energies are used as target data. The heat of formation and elastic constants of binary compounds along with substitutional and interstitial formation energies serve as binary potential calibration data, while substitutional and interstitial pair binding energies aid in developing the ternary potential. Molecular dynamics simulations employing the developed potentials predict the thermal expansion coefficient, heat capacity, self-diffusion coefficients, thermomechanical stress-strain behavior, and solid-solution strengthening mechanisms for steel alloys comparable to those reported in the literature. Interfacial energies between the steel substrate, inhibition layer, and surface oxides shed light on the interfacial nanostructures observed in the galvanizing process
EBSD: a powerful microstructure analysis technique in the field of solidification
This paper presents a few examples of the application of electron back-scatter diffraction (EBSD) to solidification problems. For directionally solidified Al-Zn samples, this technique could reveal the change in dendrite growth directions from to as the composition of zinc increases from 5 to 90 wt%. The corresponding texture evolution and grain selection mechanisms were also examined. Twinned dendrites that form under certain solidification conditions in Al-X specimens (with X = Zn, Mg, Ni, Cu) were clearly identified as dendrite trunks split in their centre by a (111) twin plane. In Zn-0.2 wt% Al hot-dip galvanized coatings on steel sheets, EBSD clearly revealed the preferential basal orientation distribution of the nuclei as well as the reinforcement of this distribution by the faster growth of dendrites. Moreover, in Al-Zn-Si coatings, misorientations as large as 10 degrees mm(-1) have been measured within individual grains. Finally, the complex band and lamellae microstructures that form in the Cu-Sn peritectic system at low growth rate could be shown to constitute a continuous network initiated from a single nucleus. EBSD also showed that the alpha and beta phases had a Kurdjumov-Sachs crystallographic relationship
Development of an electrical resistance-based corrosion monitoring system for offshore applications.
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124 p.El objetivo principal de la tesis es el desarrollo de un sistema de monitorización remota de la corrosión para estructuras off-shore (eólica y oil & gas). Mediante este sistema se pretende medir en forma remota la velocidad de corrosión de estructuras expuestas a un medio altamente agresivo como el marino, y asà conocer en tiempo real el estado de salud de las estructuras en servicio, permitiendo reducir costes de mantenimiento y reparación, etc. Las condiciones de trabajo de las estructuras offshore representan diversos retos cientÃfico-tecnológicos: El ambiente corrosivo y los fenómenos combinados de corrosión-fatiga, corrosión bajo tensión, tribocorrosión, los esfuerzos mecánicos debido al viento, olas, bloques de hielo flotante, la fragilización por hidrógeno, el biofouling en la parte sumergida, son algunos de ellos. Si bien se han llevado a cabo múltiples trabajos en el diseño de materiales y componentes offshore con el objetivo principal de incrementar la vida útil de los mismos, las condiciones extremas de trabajo a la que están sometidos estos materiales siguen representando un desafÃo que necesita de nuevos desarrollos.En la presente tesis se recogen sendos estados del arte relacionados con las diversas estructuras marinas susceptibles de ser monitorizadas por este sistema, los fenómenos de corrosión y como afectan a los materiales de interés, y estrategias sobre la protección frente a la corrosión y la monitorización de la misma. Paralelamente, se hace hincapié en el efecto de las bacterias sulfatoreductoras en la aleación de acero al carbono HSLA de grado R5 escogido en el presente proyecto. Se detalla la caracterización del acero HSLA empleado, su comportamiento frente a la corrosión comparado con otras aleaciones, una caracterización metalográfica completa que avala el uso del presente material en lÃneas de fondeo.Finalmente, se detalla de manera cronológica el desarrollo del sensor de corrosión basado en la técnica de la resistencia eléctrica, asà como la caracterización de fenómenos parásitos asociados a las medidas de baja y ultra-baja resistencia sobre el que se basa el funcionamiento del sensor
Electrokinetic Methods and Applications in Australian Aquifer Settings: High-Dimension Electrical Tomography Imaging and Neural Network Filtration Techniques
Being the driest continent in the world, there is a significant reliance on groundwater resources within many communities and industries throughout Australia. Particularly in regional areas with low rainfall and surface runoff resources, the underlying groundwater availability plays a pivotal role in population capacity and economic prosperity. Whilst the importance of groundwater resources is indisputable, many aspects of its real world homeostatic processes, in both macro and micro scales, remain difficult to decipher and explain. Within Australia’s fractured rock aquifer systems, attributed with storage of the largest volume of groundwater resources nationally, there is still only fragmented understandings of several of their principal components and capacities. This is inclusive even of key aquifer characteristics, such as total volume estimations, regeneration sources, and their flow or transportation methods. Improved modeling capabilities and techniques based on prominent and robust hydrogeological principals are continually emerging from advancing technologies, new data sources and forward thinking. However, within the field data retrieval facet of hydrological research a seemingly slower evolution is taking place. A vast quantity of aquifer information is still derived directly from intrusive observation wells. Although the plethora of information these wells can yield in modelling is invaluable, there are some profound limitations that must still be addressed. Wells are costly to establish due to drilling expenses, can only provide single point information, and can also be disruptive to the homeostasis of the system. The self-potential method is an electro-kinetic geophysical method that has recently been re-identified as an immensely promising groundwater technique. It is a fast, passive, inexpensive surface technique which requires no drilling. Uniquely and most importantly however, it is the only geophysical method that is directly sensitive to not only the presence of groundwater, but also the physical flow of groundwater due to its generation of a measurable electrical signal. Previously regarded as a predominately qualitative geophysical tool, contributing factors including advancements in low-cost instrumentation and processing capabilities have meant self-potential surveys can now provide spatially significant quantitative data for a range of groundwater modelling inputs such as permeability. The method has been recurrently reviewed since its early conception in international geophysical literature through to modern times. However, only a small quantity of this peer reviewed research has been conducted within Australia. A lesser extent of published literature therefore deals in particularly with addressing the challenges of both our harsh climate, and surface and geological conditions. With our own unique geological and hydrogeological settings, current and future challenges regarding securement of groundwater resources, and increasingly common practice of industrial geotechnical processes such as fracking, all research and findings are vital contributions to furthering our understanding of potential groundwater applications for self-potential methods on home soil. This research thesis provides analyses of multiple electro-kinetic field research projects. New self-potential datasets have been collected in the Adelaide Hills targeting stimulated fractured-rock aquifers up to 40m below surface - a considerably deep target for the method, particularly within highly conductive Australian geological conditions. Previously collected geophysical datasets from the Adelaide Hills have been reprocessed from two to four-dimensions utulising newly constructed algorithms, then reanalysed with supporting geophysical datasets. And finally, a long term (46 day) self-potential monitoring program was conducted at a commercial-use porous media aquifer to investigate novel techniques in both autonomous groundwater flow presence investigation, and environmental noise filtering methodologies for a given self-potential dataset. This research endeavors to draw further conclusion on the self-potential methods prospective as a value-adding and commercial viability modern geophysical technique in Australian groundwater research. Additionally, employing use of artificial neural networks (machine learning) for the self-potential autonomous detection and environmental noise filtration methods, we highlight the current gap in geophysical literature regarding the combination of these techniques. A light is drawn to the combined techniques immensely promising future of potential applications and contributions within the wider electrical geophysics data automation and filtration space. Much akin to our continual pursuit for mineralisation deposits, Australia is searching deeper than ever before for crucial groundwater supplies as shallower sedimentary aquifers are becoming fully utilised or depleted. As we move forward towards this new era of deepening natural resources, we must further develop both old and new tools which can enhance clarity of understanding within these challenging hydrogeological systems.Thesis (MPhil) -- University of Adelaide, School of Physical Sciences, 201
Reactive transport modeling as a tool for the integrated interpretation of laboratory and field studies in environmental geochemistry
The interaction between moving water and stationary rock within the Earth's crust and on its surface is typically controlled by a series of coupled processes occurring in porous media at various spatio-temporal scales. An example is chemical weathering, which takes place within a thin layer at the Earth’s surface called the Critical Zone and eventually leads to the formation of soils on the time-scale of hundreds to thousands of years. Chemical weathering is kinetically limited and its rate depends on the transport of CO2 and O2 through the Critical Zone. It is also strongly affected by physical weathering processes controlling the grain size distribution within the Critical Zone and thus the available mineral surface area where chemical reactions can take place. In addition, variations in biological activity that produce CO2 may change chemical weathering rates. The complex feedbacks and interrelationships within such coupled systems cannot be understood by traditional geochemical approaches that combine field observations, laboratory analyses and theoretical treatments of the individual uncoupled processes. Therefore, the quantitative interpretation of field studies requires a numerical simulation tool that is able to capture the coupled behavior of subsurface systems and to upscale experimental findings. The main requirements for such a tool are to (i) simulate the relevant geochemical and biogeochemical processes in a mechanistic way and (ii) simultaneously couple these processes to flow and transport rates. Over the past 30 years, the field of reactive transport modeling (RTM) has mastered these requirements and thus has become an essential method for the entire Earth Sciences.
This Habilitationsschrift describes the contributions by the Author to advancing the field of reactive transport modeling, thereby demonstrating how RTM enables an integrated interpretation of laboratory and/or field studies. In addition, this Habilitationsschrift emphasizes how RTM contributes to solving environmental challenges, such as those identified by the United Nations’ Sustainable Development Goals 6 (Clean Water and Sanitation), 7 (Affordable and Clean Energy), and 13 (Climate Action).
Chapter 1 introduces groundwater contamination, geothermal energy, and silicate weathering as important topics in environmental geochemistry and describes the role of coupled processes in the corresponding systems. Moreover, the Chapter introduces the general concept of reactive transport modeling and illustrates its ability to numerically capture the coupling between non-isothermal geochemical and biogeochemical processes, as well as fluid flow and transport rates.
Chapter 2 provides a detailed summary of the key accomplishments by the Author to advancing RTM. These include (i) the integration of stable isotopes in RTM simulations that address challenges relevant to environmental geochemistry, and (ii) the use of reactive transport models as an exploration tool for geothermal systems. These contributions resulted, among others, in the publication of nine peer-reviewed publications, which are presented in Chapters 3–5 and form the core of this Habilitationsschrift.
Chapter 3 presents three selected RTM applications where Cr or U isotopes are integrated in reactive transport model simulations to understand Cr- and U-contaminated groundwaters. In the first two studies, small-scale laboratory experiments are numerically simulated using a novel approach for obtaining a high spatial resolution of the simulated systems. The model results and their comparison to measured Cr and U isotope ratios provide fundamental insights into the processes controlling the magnitude of Cr and U isotope fractionation occurring in porous media. Obtaining a predictive understanding of such isotopic fractionation is crucial, because it opens the way to quantify the most important processes limiting the mobility of Cr and U in the subsurface. The third application presents a benchmarking exercise, which allowed testing and improvement of the approaches for numerically simulating stable Cr isotope fractionation in geochemical processes. Altogether, the RTM applications presented in Chapter 3 contribute to a more informed assessment and management of groundwater bodies contaminated by Cr and U.
Chapter 4 presents three applications where RTM is used as an exploration tool for geothermal systems. The first one involves 2D simulations carried out for the Dixie Valley geothermal system located in the western USA. The model output is then applied via a geochemical method called solute geothermometry, which is used to estimate the maximum temperature of deep geothermal systems. Eventually, the combined approach demonstrates which particular solute geothermometry method works best for various scenarios of rock–water interactions and thus contributes to an improved estimation of deep reservoir temperatures. Obtaining reliable temperatures is important because the reservoir temperature is a major limit on the energy that can be exploited from the deep subsurface. In the other two applications, RTM simulations are performed to quantitatively assess the geothermal potential of two geothermal systems in the Swiss Alps. All simulations are carried out in 3D and are constrained and calibrated by multiple field observations, such as chemical and isotopic compositions of thermal and cold springs, as well as temperature measurements along tunnels. The model results suggest that mountain belts such as the Swiss Alps are more promising targets for geothermal power production than previously thought, and they identify the favorable geological settings for such systems, which leads to useful implications for exploration.
Chapter 5 presents a sequence of three RTM applications, which for the first time integrate Li isotopes in the simulations. The motivation for numerically simulating the fate of Li isotopes is that their ratios serve as proxies to track and quantify the rates of silicate weathering, which in turn constitutes a major natural sink for atmospheric CO2. The first study describes a new numerical approach to integrate Li isotopes in RTM simulations. In the first and second applications, the developed approach is used to simulate the fate of Li and its isotopes in granitic and basaltic rainwater catchments, respectively. Subsequently, the model results are compared to Li data from major worldwide rivers and from a series of small streams draining the Columbia River Basalt area in the western USA. This model-based, integrated interpretation of measured Li isotope ratios permits identification of the processes governing Li isotope ratios in groundwater, riverwater and even seawater. Moreover, the results imply that seawater Li isotope ratios may be closely related to the amount of CO2 globally consumed by continental silicate weathering. In the third application, the numerical approach to simulate the fate of Li isotopes is expanded to account for the limited amount of Li that precipitates in secondary minerals. The updated approach is used to unravel a complex set of Li data collected from groundwater samples discharging into the Gotthard railway base tunnel in the Swiss Alps. This study reveals that the behavior of Li isotopes in environmental samples is more complicated than hitherto realized. Overall, the applications presented in Chapter 5 contribute to assessing the use of Li isotopes as a proxy for silicate weathering and may help to better quantify this important natural sink for CO2.
Chapter 6 summarizes the main implications of this Habilitationsschrift regarding the use of RTM in environmental geochemistry and how it contributes to meeting the listed Sustainable Development Goals. In particular, this final chapter concludes that the inclusion of stable isotopes into RTM simulations provides fundamental new insights into the processes controlling stable isotope ratios in environmental samples. This underscores how RTM serves as a powerful tool for the integrated interpretation of multiple datasets obtained from field and laboratory studies. Moreover, the Chapter discusses how RTM simulations are limited by the availability of thermodynamic and kinetic data, and by the need for detailed geochemical, biogeochemical, hydrological, and geophysical site-characterizations in order to calibrate such simulations. Finally, the Chapter contains a brief outlook emphasizing the numerous opportunities for new code development and for laboratory as well as field studies to constrain and calibrate future RTM applications. These activities will enable even more powerful RTM simulations to meet the environmental challenges of the future