Protection of a voltage source converter (VSC) based HVDC system.

Master of Science in Electrical Engineering. University of Kwa-Zulu Natal. Durban, 2017.To conserve energy and promote environmental sustainability, the power industry has invested a great deal into the generation of electricity using renewable energy (RE) sources. For such applications, high voltage direct current (HVDC) systems are considered a highly efficient alternative for bulk power transmission. Recent advances in technology favour the use of voltage source converter (VSC) based HVDC systems for the integration of RE sources. These schemes are favoured for their controllability and provide major reinforcements to the power systems. Despite its promising future, the technology is constrained by the unavailability of a reliable protection scheme, as the operating times for HVDC protection schemes are required to be ten to a hundred times faster than existing AC protection algorithms. VSC-HVDC networks are usually more vulnerable to DC-side faults. Selective protection against these faults is therefore essential for safe and reliable operation of the network. This study provides the necessary concepts to develop VSC-HVDC protection algorithms for multi-terminal (MT) meshed HVDC systems. DC fault characteristics were initially investigated. They provided a basic understanding of the VSCs natural responses to DC fault scenarios. The study also focused on analysing factors that may adversely influence the systems protection performance. These include the DC fault distance, DC-link conductor sizes and DC fault impedance. Results obtained from these variations show that the DC-link capacitor was one of the main sources that cause the high rise of DC fault currents and that these are the highest and the most dangerous when closest to the converter station. With a clear understanding of the DC fault characteristics, a protection scheme has been proposed. Initially, different methods are discussed with the intent of deciding on the scheme that is the most suitable. Detection techniques based on the discrete wavelet transform (DWT) for primary protection and the current derivative technique for back-up were chosen as the most promising. These techniques offer accuracy, speed and selectivity which are factors that are all important for the network. The single VSC terminal travelling wave technique was implemented to identify the exact position of a DC fault. This method reduces costs as it eliminates the need of communication links. Finally, to isolate the affected cables, the hybrid DC circuit breakers (CB) were implemented into the VSC-HVDC system. The CBs have been coupled with a reactance for fault current limiting and to isolate the system before it reaches an uninterruptable current magnitude. Back-up AC CBs were included on the AC side of the network and were stationed to separate the VSC network from the AC grid in cases where the implemented primary protection scheme fails

Interactive advertising displays

Interactive public displays are the latest development in the field of out-of-home advertising. Throughout history characteristic shapes for billboards evolved such as flat rectangular displays, long displays or cylindrical advertising columns. This work presents novel interactive display designs that are based on these historical role models and allow passers-by to interact with them in a natural, touchless manner. It further pursues a vision where interactive public displays become more active themselves and actively influence passer-by behavior in order to increase their effectiveness, better attract attention and improve public interaction in front of them. First, to overcome the challenge that passers-by often do not expect public displays to be interactive and thus pay no attention to them, this work presents a solution called unaware initial interaction that surprises passers-by and communicates interactivity by giving visual feedback to their initial movements. To be effective, the visual feedback has to be designed considering the specific display shapes, their requirements to contents and the typical approaching trajectories. Second, to overcome the challenge that larger groups of passers-by often crowd together in front of wide public displays or do not take optimal positions for interaction, this work presents a solution to subtly and actively guide users by dynamic and interactive visual cues on the screen in order to better distribute them. To explore these concepts and following an initial analysis of the out-of-home domain and of typical display qualities, interactive counterparts to the classical display shapes are designed such as interactive advertising columns, long banner displays and life-size screens. Then interactive contents and visual feedbacks are designed which implement the presented interactivity concepts, and audience behavior around them is analyzed in several long-term field studies in public space. Finally the observed passer-by and user behavior and the effectiveness of the display and content designs are discussed and takeaways given that are useful for practitioners and researchers in the field of public interaction with out-of-home displays.Interaktive öffentliche Displays sind die neueste Entwicklung im Bereich der Außenwerbung. Im Laufe der Geschichte bildeten sich charakteristische Formen für Werbetafeln heraus wie flache rechteckige Displays, lange Displays oder zylindrische Werbesäulen. Die vorliegende Arbeit stellt neuartige Designs für Displays vor, die auf diesen historischen Vorbildern aufbauen und den Passanten erlauben, mit ihnen auf eine natürliche, berührungslose Art und Weise zu interagieren. Darüber hinaus verfolgt sie eine Vision, in der interaktive öffentliche Displays aktiver werden und entsprechend das Passantenverhalten beeinflussen, um ihre Wirksamkeit zu erhöhen, mehr Aufmerksamkeit auf sich zu ziehen und die öffentliche Interaktion mit ihnen zu verbessern. Zunächst stellt diese Arbeit eine als Unbewusste Initialinteraktion bezeichnete Lösung vor, welche die Passanten überrascht und mittels visuellem Feedback auf ihre anfänglichen Bewegungen Interaktivität übermittelt, um die Herausforderung zu bewältigen, dass Passanten oft nicht erwarten, dass öffentliche Displays interaktiv sind und sie ihnen somit keine Aufmerksamkeit schenken. Um effektiv zu sein, muss das visuelle Feedback dabei so gestaltet werden, dass es die spezifischen Displayformen, ihre Anforderungen an die dargestellten Inhalte und ihre typischen Annäherungswege berücksichtigt. Zweitens stellt sie eine Lösung vor, bei der die Nutzer auf subtile Weise und durch auf dem Bildschirm dargestellte dynamische und interaktive visuelle Reize aktiv geführt werden, um sie besser vor dem Display zu verteilen, um die Herausforderung zu bewältigen, dass größere Gruppen von Passanten sich oft vor breiten öffentlichen Displays zusammendrängen oder keine optimalen Positionen für die Interaktion einnehmen. Zur Erforschung dieser Konzepte werden im Anschluss an eine einführende Analyse von Außenwerbedisplays und ihrer typischen Eigenschaften interaktive Entsprechungen der klassischen Displayformen entwickelt wie interaktive Litfaßsäulen, lange Bannerdisplays und Life-size Screens. Weiter werden für diese Displays interaktive Inhalte und visuelle Feedbacks entwickelt, welche die vorgestellten Interaktivitätskonzepte umsetzen und das Verhalten des anwesenden Publikums in mehreren Langzeit-Feldstudien im öffentlichen Raum untersucht. Schließlich werden das beobachtete Passanten- und Nutzerverhalten und die Effektivität der entwickelten Display-Designs und Inhalte bewertet und nützliche Empfehlungen für Praktiker und Forscher auf dem Gebiet der öffentlichen Interaktion mit Außenwerbedisplays gegeben

Communicative humanoids : a computational model of psychosocial dialogue skills

Thesis (Ph. D.)--Massachusetts Institute of Technology, Program in Media Arts & Sciences, 1996.Includes bibliographical references (p. [223]-238).Kristinn Rúnar Thórisson.Ph.D

From tool to instrument: An experiential analysis of interacting with Information Visualization.

Information Visualizations (InfoVis) are tools that represent huge amount of abstract data visually on a computer screen. These tools are not reaching the users since constituents of good InfoVis design are still an unknown. In this thesis I argue that good design is one that delivers positive experiences due to the subjectivity of the knowledge gaining processes. Hence, what constitutes a positive experience is the focus of this research. The application domain chosen was the Academic Literature Domain (ALD). ALD InfoVis tools exist however they do not cater for users' requirements or interface usability, both of which are crucial for a better experience. As a result, an ALD InfoVis tool was created following a User Centred Design (UCD) approach, starting with requirements and ending with usability. The requirements were first generated based on a qualitative study from which it became clear that researchers equate authors with their publications and position them in terms of the ideas they portray. Based on this, the tool was designed and implemented. The tool's usability was then evaluated through a set of low and high level tasks. Low-level tasks target the visual syntax whereas high-level tasks tap into the generated semantics. The latter allowed for subjective reasoning and interaction, and were therefore used as the basis of the experiential study. The experiential study captured users' experiences by relying on a Grounded Theory (GT) analysis. This study resulted in the generation of a base theory of InfoVis interaction that properly fitted within the context of the instrumental genesis theoretical framework which argues for the design of instruments not tools, where instruments are mental appropriations of tools. The theoretical approach applied by this research has value across InfoVis even if not tailored for evaluation

Supporting the grow-and-prune model for evolving software product lines

207 p.Software Product Lines (SPLs) aim at supporting the development of a whole family of software products through a systematic reuse of shared assets. To this end, SPL development is separated into two interrelated processes: (1) domain engineering (DE), where the scope and variability of the system is defined and reusable core-assets are developed; and (2) application engineering (AE), where products are derived by selecting core assets and resolving variability. Evolution in SPLs is considered to be more challenging than in traditional systems, as both core-assets and products need to co-evolve. The so-called grow-and-prune model has proven great flexibility to incrementally evolve an SPL by letting the products grow, and later prune the product functionalities deemed useful by refactoring and merging them back to the reusable SPL core-asset base. This Thesis aims at supporting the grow-and-prune model as for initiating and enacting the pruning. Initiating the pruning requires SPL engineers to conduct customization analysis, i.e. analyzing how products have changed the core-assets. Customization analysis aims at identifying interesting product customizations to be ported to the core-asset base. However, existing tools do not fulfill engineers needs to conduct this practice. To address this issue, this Thesis elaborates on the SPL engineers' needs when conducting customization analysis, and proposes a data-warehouse approach to help SPL engineers on the analysis. Once the interesting customizations have been identified, the pruning needs to be enacted. This means that product code needs to be ported to the core-asset realm, while products are upgraded with newer functionalities and bug-fixes available in newer core-asset releases. Herein, synchronizing both parties through sync paths is required. However, the state of-the-art tools are not tailored to SPL sync paths, and this hinders synchronizing core-assets and products. To address this issue, this Thesis proposes to leverage existing Version Control Systems (i.e. git/Github) to provide sync operations as first-class construct

The efficacy of lignosulfonate in controlling the swell potential of expansive soil and its stabilization mechanisms

Many techniques have been developed and applied to prevent and/or remediate infrastructural damage caused by expansive soils throughout the world. Of these techniques, traditional chemical (lime and cement) stabilization has gained world attention because of a good understanding of the underlying mechanisms, availability of technical guidelines, and years of demonstrated field experiences. However, despite the global acceptance of traditional additives for treating expansive soil, other environmentally benign alternatives have been an important subject of research due to the inherent health and safety concerns for traditional admixtures. One such alternative is from the paper industry that manufactures pulp from wood and in the process produces over 50 million tons annually of a waste substance known as lignosulfonate (LS). This substance has been disposed of as a waste product resulting in colossal disposal cost; however, it does have a potential application in geotechnical engineering under the concept of sustainable development. This investigation into LS admixture consists of experimental and theoretical studies. The experimental investigation involved a laboratory evaluation of the efficacy of LS admixture in controlling the swell potential of a remoulded expansive soil. The swell potential was examined in terms of percent swell and swell pressure of the soil. In addition to these engineering properties, the Atterberg limits, unconfined compressive strength, durability (wet/dry and freeze/thaw), compaction characteristics, permeability, consolidation characteristics, and shrinkage behaviours were also investigated. Furthermore, the mechanism by which the remoulded soil was modified or altered by the LS admixture was probed and identified. The optimum content of LS admixture was found to be about 2% by dry weight of the soil. Standard geotechnical laboratory tests performed on untreated and treated compacted soil specimens showed significant and consistent changes in the swell potential and other engineering properties such that the percent swell decreased by 22% while maintaining the soil’s pH. In some instances, identical specimens treated with 2% cement were prepared and tested for comparison. Although the specimens treated with cement recorded a 33% reduction in the percent swell, the ductile characteristics were replaced by brittleness and a significant increase in pH. Further analysis of the laboratory test data also suggested that LS admixture is a resourceful alternative for “low” swelling soils. This finding led to the formation of a “LS application chart” that will help geotechnical practitioners on admixture choice for a particular expansive soil deposits. The physical-chemical analyses of untreated and 2% LS treated specimens were studied microstructurally after 7 days of curing. When LS was added into expansive soil, the stabilization mechanisms consisted of an insignificant exchange of interlayer cations due to the “cover-up-effect”, basal/peripheral adsorption on mineral surfaces through hydrogen bonding (water bridging), direct bonding to dehydrated cations with the subsequent formation of flocculation-aggregates, initial expansion of diffuse double layer and water entrapment, and a waterproofing effect. An elemental analysis of untreated and treated specimens suggested inter-molecular interactions between soil minerals and the LS admixture as opposed to major chemical reactions. Thus, LS summarily altered the crystallographic characteristics of the soil minerals, and helped to reduce shrink-swell behaviour of the otherwise expansive soil. The theoretical aspect of this research work involved the development of a robust mathematical model to predict the swell behaviour of expansive soil treated with LS. Relationships were proposed to estimate the suction behaviour of treated soil using laboratory data obtained experimentally. Suction behaviour was governed by a single constant (β), which depends on an input variable; the degree of saturation (Sd). A reasonable correlation was found between the percent swell determined experimentally and the predicted values. A non-traditional admixture such as LS has the potential to become a technically and economically competitive alternative in the stabilization of expansive soils. With over 50 million tons being produced annually, the successful use of LS admixture as a new stabilization material for expansive soil appears to be one of many viable solutions to the sustainable use of a waste by-product, green construction, and as well as saving the disposal problems inherent in the paper manufacturing industry

Top 10 technologies and their impact on CPA\u27s

https://egrove.olemiss.edu/aicpa_guides/2474/thumbnail.jp