Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1993. / Vita. Abstract. Includes bibliographical references (leaves 61-62). Also available via the Internet.

As the world strives towards finding alternative sources of power generation, photovoltaic generation has become an increasingly prevalent alternative energy source on power systems world-wide. This paper studies the effects that incorporating photovoltaic generation has on the existing power systems and their power system protection schemes. Along with the addition of this emerging alternative energy source comes the volatility of PV power generation as cloud-cover produces erratic variations in solar irradiance and PV power production. Such variations in PV power may lead to unfavorable operating conditions and power system failures. The issues addressed in this paper include a study of inverter harmonic levels for variations in DC voltage and power, and a study of power system protection failures caused by cloud-induced PV power variations. Such issues are addressed so as to provide a better understanding of the effects that cloud-induced PV power generation variability has on power systems and its protection schemes.

published_or_final_version / Electrical Engineering / Master / Master of Science in Engineering

Hemoglobin-based oxygen carriers for use as transfusion fluids have emerged as a leading technology directed at stemming shortages of a safe blood supply and providing a readily available resuscitation fluid in various trauma situations. The purpose of this investigation was to determine the effects of isovolemic hemodilution with Hespan and a hemoglobin-based oxygen carrier (HBOC) on erythrocyte-associated transients (EATs) in capillary PO2. The particulate nature of blood flow in capillaries, when observed from a stationary observation point, results in fluctuations of PO2 as alternating red blood cells and plasma gaps move through the detection region. Therefore, through experimental methods which provided the necessary temporal and spatial resolution required to make such measurements, EATs can be observed and corresponding PO2 fluctuations can be determined. The spinotrapezius muscle in sixteen Sprague-Dawley rats was exteriorized for intravital microscopy measurements in capillaries. Capillary PO2 was measured using Pd-porphyrin phosphorescence quenching microcopy. The hemodiluents used in isovolemic hemodilution included Hespan, a non-oxygen carrying plasma expander, and Oxyglobin®, a HBOC. Two isovolemic hemodilution steps were performed, reducing the systemic hematocrit to an average of 27.5% after the first step and 13.5% after the second step. Results showed that erythrocyte-associated transients in PO2 can be observed in the rat spinotrapezius with significant differences occurring between red blood cell and plasma gap PO2 under control conditions, isovolemic hemodilution with Oxyglobin after step one, and isovolemic hemodilution with Hespan after step two. This study concludes that EATs are observable and PO2 transients relating to EATs can be measured in the rat spinotrapezius muscle. Furthermore, it can be concluded that the HBOC Oxyglobin caused a decrease in erythrocyte-associated capillary PO2 transients, as well as a general decrease in capillary PO2. In addition, this study concludes that erythrocyte-associated capillary PO2 transients can best be observed under control conditions and after step two of isovolemic hemodilution with Hespan.

A dissertation submitted to the Faculty of Engineering and the Built Environment, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Master of Science in Engineering in the High Voltage Research Group School of Electrical and Information Engineering Johannesburg, June 2017 South Africa / Servitude availability in space-constrained built-up areas within the Johannesburg or Central Load Network (CLN) poses every-day challenges for power system engineers. Strengthening the backbone 88/275 kV transmission system within the CLN becomes even more difficult when multi-circuit transmission lines are required for increased power transfer capabilities. When uprating is considered to increase the power transfer capability, the withstand levels of existing external insulation demands an optimisation to find a new stress versus strength balance that allows reliable operation of substations at higher voltages. The research includes primarily an investigative simulation study to evaluate the current Eskom available design clearances in terms of their withstand capability when subjected to over-voltage transients. Two voltage range classes were evaluated and the results are discussed. For voltage range 1, it was found that the over-voltage stress was low enough to allow for a higher nominal operating voltage while maintaining the existing clearances. For voltage range 2, existing clearances are also found to be conservative and smaller safety margins will most likely be acceptable. From a transient analysis evaluation, voltage uprating is considered as a very attractive option to increase the power transfer capability of existing substations. Current Eskom clearances for 88 kV and 275 kV are expected to perform well during transients generated in uprated systems. Electrode grading to improve the field gradients in the substation will require attention to increase gap factors. Additional surge arresters are considered to be a cost effective solution to control over-voltages throughout the whole uprated substation. The physical modification of substations to replace strung conductors with tubular conductors, ensuring sufficient outage time to refurbish and rebuild with new equipment will be the most challenging part of uprating existing substations. / MT 2017

A dissertation submitted to the School of Public Health, University of the Witwatersrand, in fulfillment of the requirements for the degree of Master of Science in Medicine by research and dissertation. 07 June 2016 / Introduction: Migrant farm workers in South Africa are particularly vulnerable to HIV infection for a multitude of reasons, including a lack of access to health services and to health information. Social norms on the farms, including an acceptance of multiple concurrent sexual partners and transactional sex both for comfort and material gain, tend to worsen women's powerlessness to manage effectively their sexual reproductive health. High levels of stigma also mean that the risks of HIV infection cannot easily be spoken about, further increasing vulnerability. The Hlokomela project sought to use participatory communication processes to empower peer communicators on the farms to engage farm workers in regular, structured discussions on HIV /AIDS and other health and wellness related matters, including difficult conversations around gender inequity. The making of a collective identity for the project was one of these participatory processes. Its novelty in this setting warranted research to answer the question "How does (or does) the collective making of a project identity help to promote health on the farms of Hoedspruit?". Aim: The aim of the research was to describe and analyse the role of collective identitymaking in the Hlokomela project, an intervention to address vulnerability to HIV among migrant and seasonal farm workers in Hoedspruit, Limpopo province, South Africa. The study aimed also to propose and further develop, in the light of Findings, a conceptual framework which would help to explain the effects of the various elements of collective identity-making. Methods: The research is a qualitative study of the collective identity-making component of the Hlokomela health project. Elements of a grounded theory approach were adopted in the three successive data collection site visits, enabling progressive coding of the data as the collection occurred. Data was collected through two Focus Group Discussions (FGD) with Nompilos (farm worker volunteer peer communicators and care givers) and two FGDs with Gingirikani (farm worker volunteer peer communicators chosen by Nompilos and farm workers to be their deputies on the farms, to facilitate purposive dialogues and thus increase reach). There were also 10 individual in-depth interviews with other key stakeholders and three small group interviews (2-3 respondents) with Hlokomela managers and co-ordinators. All interviews were audio-taped, transcribed and where necessary translated into English from Xitsonga and Sepedi. The voices of those most directly affected by the intervention formed the basis for coding and analysis. Findings: The development of the collective identity through participatory processes was found to enhance engagement with and among farm workers. This was due to the project's perceived pertinence and local ownership. The collective identity was seen to be relevant and expressing a farm worker reality. Farm workers generally described feeling affirmed, seeing themselves projected into a public space that had hitherto not been open to them. And also in particular, the agents of the project – the Nompilos and their "deputies" the Gingirikani – described at length how being associated with Hlokomela gave them the authority and credentials to work with farm workers on sensitive matters, including establishing a set of values and norms which would be health-protective but which also involved a shift in what was considered possible and desirable. There was furthermore a sense of belonging to the project, not only on the part of the primary "beneficiaries" – farm workers – but also of other stakeholders, including farm owners/managers, municipal office bearers, and local health workers. This bridging social capital further augmented the project's capacity to reach farm workers by, for example, enabling access in working time on the farms, by donations in money and in kind by the local community, and by making visible and normal what hitherto had been hidden – particularly in terms of gender equity and a softening of hegemonic masculinities. Farm workers could take the lead, and women could take the lead also. Conclusions: The collective identity-making work of Hlokomela had aided the project's agents to nurture a new possible, founded in a slightly altered set of values and norms, which had the potential to reduce vulnerability to HIV infection. The elaboration of a social institution, largely in the symbolic space, had authorised the project's agents, in their own eyes as well as those of their peers, to carry out their often difficult work of facilitating regular dialogues on hitherto rarely broached topics, including gender relations and risky sexual behaviour. The findings indicate a need for further research into the cost effectiveness and replicability of this kind of identity work in similar projects, perhaps with the addition of quantitative assessments of the extent of projects' reach through collective identity work as well as the value of collateral beneficial effects to participants in resource poor settings. / MT2016

In a risk situation the flow through a hydropower turbine must be reduced under a short amount of time. The reduction in flow causes low pressures in the region called draft tube under the runner in the turbine. If the pressure drops below vapor pressure the water in the turbine may evaporate and form large cavities. The phenomenon called water column separation describes the situation when these cavities of vapor forms and eventually collapses which may damage the unit and canbe a danger to personnel at site. Different types of flow reducing maneuvers are tested before commissioning turbines in order to detect dangerously low pressures but these measurements can be difficult to interpret. The measured draft tube pressure can be filtered numerous ways and in addition other measured or calculated parameters must be studied to fully understand the consequence of a measured emergency stop. In this paper the different ways of filtering and interpreting the measurements from stops in Kaplan turbines were analyzed. The results show that the choice of filtering method can significantly impact the interpretation of a stop and that the filter parameters often used do not result in equivalent results. The standard way to filter draft tube pressure with moving average filters is shown to result in much higher draft tube pressures than low-pass filters and the filter parameter used needs to be further investigated to correctly isolate pressures caused by water column separation. The main difference between different companies when it comes to these measurements are the used cutoff frequency when using low-pass filters and the sampling frequency of measurements.

Atualmente, os avanços tecnológicos, especialmente dos recursos computacionais, possibilitam a realização de cálculos cada vez mais complexos. Em função destes avanços, transitórios hidráulicos antes desprezados ou estimados de forma rudimentar já podem ser calculados, especialmente nos casos em que o comportamento dos transitórios é crítico. Assim, torna-se necessário o desenvolvimento de métodos de cálculo que permitam prever quantitativamente tais transitórios uma vez que não há solução analítica para este problema. Neste trabalho são estudadas as condições de contorno para a utilização do modelo rígido de coluna líquida e sua respectiva solução numérica para o cálculo de transitórios durante o enchimento de uma tabulação com ramificação. Os modelos matemáticos foram testados em laboratório sob diversas condições, comprovando a viabilidade da utilização das ferramentas teóricas e numéricas desenvolvidas. / Nowadays there have been many technological advances, especially related to computational resources, that make possible more complex and huge calculations. Due to these advances, the evaluation of hydraulics transients, which have been disregarded or roughly estimated, is allowed to be more precisely performed especially when transient phenomena have significant importance. Then, the development of calculating methods that evaluates these transients effects becomes necessary once the analitic solution to these problems does not exist. This work presents the study of the boundary conditions of the rigid model applied to the fluid column and its numeral solution in order to calculate the transient behavior during filling of pipeline with ramifications. The results of mathematical models were compared with those from laboratory experiments under several conditions proving the feasibility of theoretical and numeral models.

Esta dissertação descreve um simulador em tempo real para aplicação em testes de reguladores de velocidade de hidrelétricas. O simulador é implementado num hardware que permite a conexão física de todos os sinais que o regulador teria na usina. As dimensões e o perfil hidráulico da usina, dados das máquinas e unidade de força hidráulica são inseridos através de tabelas de fácil entendimento pelo usuário Os transientes hidráulicos no conduto forçado são simulados usando o método das características e levam em conta a influência da turbina. A unidade hidráulica e os atuadores são modelados incluindo suas não-linearidades. Além dos testes de fábrica, este simulador pode ser utilizado para análise preliminar de transientes hidráulicos, treinamento de operadores e como plataforma de testes para novas estratégias de controle da turbina. / This work describes a real-time simulator to be used in hydroturbine speed governor tests. The simulator is implemented using a hardware configuration which allows the physical connection to the governor under test like it would be in the hydropower plant. The conduit dimensions, hydraulic scheme, machine and hydraulic power unit data are inserted into the simulator by user friendly input tables. The hydraulic transients in the penstock are simulated using the method of characteristics and take into account the turbine influence. The electrohydraulic interface, servomotor and hydraulic power unit are simulated including the nonlinearities of valves and servomotors. Besides the factory tests, this simulator can also be applied for a preliminary analysis of hydraulic transients, operator training and platform for testing new turbine control strategies.

O presente trabalho versa sobre o termo de atrito em escoamento transitório em condutos forçados, partindo de uma modelação matemática da tensão de cisalhamento transiente, usando conceitos do princípio da entropia máxima. Usa-se a modelação deste termo de atrito na análise do transitório hidráulico, comparando-se com dados experimentais já publicados de um sistema Reservatório-Tubo-Válvula. / This report contains a friction term for hydraulic transient in closed conduits. We use a mathematical model for the shear stress, derived by principle of maximum entropy. Then, we use this friction term for an analysis in a system reservoir-tube-valve, comparing our results with anothers already published in the literature.