The increasing penetration of renewable energy resources within the Great Britain (GB) transmission system has created much greater variability of power flows within the transmission network. Consequently, modern transmission networks are presented with an ever increasing range of operating conditions. As a result, decision making in the Electricity National Control Centre (ENCC) of the GB electrical power transmission system is becoming more complex and control room actions are required for reducing timescales in the future so as to enable optimum operation of the system. To maximise utilisation of the electricity transmission system there is a requirement for fast transient and dynamic stability control. In this regard, GB electrical power transmissions system reinforcement using new technology, such as High Voltage Direct Current (HVDC) links and Thyristor-Controlled Series Compensation (TCSC), is planned to come into operation. The research aim of this PhD thesis is to fully investigate the effects of HVDC lines on power system small-disturbance stability in the presence of operational uncertainties. The main research outcome is the comprehensive probabilistic assessment of the stability improvements that can be achieved through the use of supplementary damping control when applied to HVDC systems. In this thesis, two control schemes for small-signal dynamic stability enhancement of an embedded HVDC link are proposed: Modal Linear Quadratic Gaussian (MLQG) controller and Model Predictive Controller (MPC). Following these studies, probabilistic methodologies are developed in order to test of the robustness of HVDC based damping controllers, which involves using classification techniques to identify possible mitigation options for power system operators. The Monte Carlo (MC) and Point Estimated Method (PEM) are developed in order to identify the statistical distributions of critical modes of a power system in the presence of uncertainties. In addition, eigenvalue sensitivity analysis is devised and demonstrated to ensure accurate results when the PEM is used with test systems. Finally, the concepts and techniques introduced in the thesis are combined to investigate robustness for the widely adopted MLQG controller and the recently introduced MPC, which are designed as the supplementary controls of an embedded HVDC link for damping inter-area oscillations. Power system controllers are designed using a linearised model of the system and tuned for a nominal operating point. The assumption is made that the system will be operating within an acceptable proximity range of its nominal operating condition and that the uncertainty created by changes within each operating point can possibly have an adverse effect on the controller’s performance.

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Development on dolomite poses a risk due to the possible formation of instability features such as sinkholes. Most of these features are however man-induced, and the risk associated with development on dolomitic areas can be mitigated through correct management. Therefore, since the Tlokwe City Council is accountable for safe development within its jurisdiction, a Dolomite Risk Management Strategy (DRMS) should be put in place. There are several factors that contribute to the risk for development on dolomite. These factors can be catagorised into two groups that should be considered during the hazard identification process, namely physical factors that consists of geology, geohydrology and geotechnical, and anthropogenic factors that consists of existing infrastructure and development, land use planning, as well as social structure and awareness. These factors are assessed by means of a risk assessment in order to obtain a disaster risk score for different areas within the study area. Based on this score, priority focus areas can be identified, mainly for critically important further research before any development can be allowed or mitigation measures implemented. Once these research activities are completed, a DRMS can be compiled based on the guidelines set by SANS 1936, which will promote the safety of people and property when further development on dolomite takes place. Urgent and interim mitigation measures are proposed to manage the risk during further research activities. / Thesis (MSc (Environmental Sciences))--North-West University, Potchefstroom Campus, 2013

Development on dolomite poses a risk due to the possible formation of instability features such as sinkholes. Most of these features are however man-induced, and the risk associated with development on dolomitic areas can be mitigated through correct management. Therefore, since the Tlokwe City Council is accountable for safe development within its jurisdiction, a Dolomite Risk Management Strategy (DRMS) should be put in place. There are several factors that contribute to the risk for development on dolomite. These factors can be catagorised into two groups that should be considered during the hazard identification process, namely physical factors that consists of geology, geohydrology and geotechnical, and anthropogenic factors that consists of existing infrastructure and development, land use planning, as well as social structure and awareness. These factors are assessed by means of a risk assessment in order to obtain a disaster risk score for different areas within the study area. Based on this score, priority focus areas can be identified, mainly for critically important further research before any development can be allowed or mitigation measures implemented. Once these research activities are completed, a DRMS can be compiled based on the guidelines set by SANS 1936, which will promote the safety of people and property when further development on dolomite takes place. Urgent and interim mitigation measures are proposed to manage the risk during further research activities. / Thesis (MSc (Environmental Sciences))--North-West University, Potchefstroom Campus, 2013

Une structure de contrôle distribué partiellement coopérative est proposée dans cette thèse. La structure est consacrée au problème de commande d’un réseau composé de sous-systèmes non linéaires/linéaires qui sont interconnectés par leurs états et les entrées de commande. Par la coopération partielle, cela signifie que chaque sous-système est capable de préserver son propre objectif en utilisant un indice de la coopération ajustable qui définit dans quelle mesure il accepte de dégrader son propre niveau de performance afin d’aider ses voisins à maintenir leur intégrité sous les interconnexions potentiellement déstabilisantes. La communication entre les sous-systèmes est basée sur l’échange de niveaux de fonction de Lyapunov avec les contraintes associées et la quantité d’information transmise est plutôt réduite par rapport aux travaux les plus récents. Une autre caractéristique intéressante de cet structure de contrôle distribué non linéaire coopératif est l’utilisation de vecteurs prioritaires par chaque sous-système. Ce vecteur définit un ordre hiérarchique de l’importance de ses voisins menant à une stratégie de coopération dans lequel les sous-systèmes critiques dans le réseau peuvent être préservés en dépit des interactions. Une version linéaire de la structure de contrôle distribué coopératif est présenté. Cette conception de structure linéaire conduit à une évaluation rigoureuse de stabilité du réseau en boucle fermée globale. Une méthode d’amélioration de la stabilité est proposée basée sur la résolution d’un problème d’optimisation non convexe avec des degrés de liberté liés au paramétrage de l’affectation de priorité. Pour montrer son efficacité, le contrôle distribué coopératif proposé pour le réseau linéaire est appliqué pour traiter le problème de contrôle de la fréquence de charge dans un réseau d’alimentation et le problème de contrôle du système cryogénique. / In this dissertation, a partially cooperative distributed control framework is proposed. The framework is dedicated to the control problem for a network consisting of linear/nonlinear subsystems that are interconnected through their states and control inputs. By partial cooperation, it means that each subsystem is able to preserve its own objective while using a tunable cooperation index that defines to what extend it accepts to degrade its own performance level so as to help its neighbors maintain their integrity under potentially destabilizing interconnections. The communication between the subsystems is rather reduced comparing to most of the existing contributions. Another attractive feature of the proposed framework is that each subsystem in the network can be assigned with priority indicating the importance of the corresponding subsystem seen by its neighbors. Through proper parameterization of the priority assignment, improved performance of the subsystems and the network can be acheived. In the linear version, a rigorous stability assessment method is presented and a systematic way of proposing an optimized priority assignment for a given network is introduced as well. The proposed scheme is applied to handle the load frequency control problem in a 4-area power network and the control problem of a cryogenic system to illustrate its effectiveness.

Study of Production Drifts Stability and Assessment of Reinforcement Requirements at LKAB Konsuln Test-Mine Levels 436 and 486 Using Geologic Structures Data, and Modelling Software - Dips and Unwedge:  a Part of dp1 Project (Mine Layout and Technology) of the Sustainable Underground Mining (Sum) Project Oludare Joseph Olufe Global population has been on exponential increase over the past half century. The population explosion is driving massive urbanization and infrastructure developments across the globe, which result in huge demand for metals, especially steel. The trend is forecasted to continue to rise steeply in for the next two decades. This is putting enormous strain on metals mining, especially because new surface economic deposits are rare to come by. Therefore, mining is steadily going deeper in many of the mining destinations across the world.     Mining at great depths present unique challenges, particularly regarding stability of excavations at depths. Rock falls, rock burst, excavation collapse are common occurrences associated with deep mining. In regions with high seismicity potentials the frequency and consequences could be very high. Over the past decade ground instability has become a significant challenge confronting mining at LKAB deep mines. There had been incidents that resulted in long term closure of sections of the mines, with resultant adverse economic impacts. More undesirable is loss of live of personnel.     The study was conducted at the Konsuln test mine levels 436 and 486, aimed to investigate the impacts of geologic structures on excavations instability at depths, at the Kiruna iron ore mines, on one hand.  And on the other hand, evaluate the influence of geologic structures on ground reinforcements at the mine. Structural data were collected and analysed using Dips program to define orientation of major structures. The results were used for wedge analysis and excavations stability modelling using Unwedge program. Important rock mechanical parameters were defined based on data provided, and others based on literatures. A design factor of safety of 1.5 was used.     Results from the study established that structures have significant impact on excavations instability at the Konsuln mine. 100% of the production drifts studied has minimum of four wedges formed in its perimeters. Out of this approximately 37% has factor of safety lower than 1.5. Evaluation of reinforcements (shotcrete and rock bolts) implemented in the mine found that approximately 15% of the total wedges formed in the production drifts has factor of safety less that 1.5 after both shotcrete and rock bolt reinforcements had been implement. Also, approximately 5% of the total wedges has apex height longer the rock bolt length.     It was therefore concluded that structurally induced instability is a major contributor to excavations instability at the Kiruna mine. The study approach presented a new methodology to understand and provide robust solution to ground instability problem at the mine.

Renewable energy is playing an increasingly significant role in power system operation and stability assessment with its numerous penetration expansion. This is not only brought by its uncertain power output and inverter-based equipment structures but also its operation characteristics like Low Voltage Ride Through (LVRT). It is thus necessary to take these characteristics into consideration and further to find more adaptive schemes to implement them for more effective analysis and safer power system operation. All the aforementioned is based on the accurate identification of the system fundamental information. In this dissertation, a systematic approach is proposed to find the valid system model by estimating the transmission line parameters in the system with PMU measurements. The system transient stability assessment is conducted based on this validated model. The constrained stability region is estimated with Lyapunov functions family based method in the center of angles reference frame considering renewables LVRT as operation limits. In order to integrate the LVRT constraints, a polytopic inner approximation mechanism is introduced to linearize and organize the transformed constraints in state space, which brings much scalability to the whole process. From the voltage stability perspective, an approach to adaptively adjust LVRT settings of the renewable energy sources in the system is formulated to guarantee the system load margin and thus the voltage security. A voltage prediction method is introduced for critical renewable energy sources identification. Estimation methods based on interpolation and sensitivities are developed and conducted for saving computation effort brought by continuation power flows. Multiple test cases are studied utilizing the proposed approaches and results are demonstrated. / Doctor of Philosophy / Renewable energy utilization is continuously rising nowadays. They are clean but highly dependent on natural resources, which causes their uncertainty and intermittence in electric power output. The power system, on the other hand, is designed for schedulable and controllable power generators, which make the traditional methods for system operation and analysis of the system stability much less effective facing the trend of renewables integration. In this dissertation, a series of systematic approaches are proposed firstly identify the system parameters for more accurate system modeling through PMU measurements, then to assess the system transient stability considering the renewable energy sources operation limits, and finally to adaptively adjust these operation limit for improving the system voltage security. The operation limits are transferred into the form in terms of system states. Linearization and approximation methods are also introduced to enhance the scalability of the processes. Multiple test cases are studied with the proposed approaches and the results demonstrate their effectiveness and efficiency.

Title: Postural stabilization and balance - theoretical background and definitions (literature review) Objectives: The aim of this theses is to investigate the present situation of theoretical background of postural stabilization and balance and find out the differences between both of these phenomenons. The theses should summarize the current literature including the newest studies. Furthermore, it discusses the most used computerized measurements methods for assessing balance and postural control. Methods: The theses has character of literature review. It is divided into several parts. The beginning introduces the theoretical background. The descriptive and analytical chapter discuss the most used computerized measurement methods for assessing balance and postural control. The discussion summarizes the current situation and results of the theses. Results: The total amount of the 104 studies was found, but only 12 of them met the criteria of the theses. Currently the most used methods for assessing balance and postural control are the computerized dynamic posturography and the visual feedback posturography. In the published studies there were found several differences in the methods of posturography. Even, there was revealed ideological diversity in the authors' opinions and disunity in...

Voltage stability is the ability of the power system to maintain steady acceptable voltages at all the buses in a system under normal operating conditions and after being subjected to a disturbance. The increased consumption of electricity without the augmentation of the necessary transmission infrastructure has resulted in the overloading of the transmission lines. As a result, the transmission lines operate near the steady state stability limit. The transmission of large amounts of power through the lines results in the large voltage drops in the lines. Sudden disturbances like line or generator outage and fault in the transmission lines may occur because of natural or man made causes. Under the above mentioned conditions, the transmission system may not be able to supply the load demand. This results in drops in the system bus voltages which may be sudden or progressive. If the necessary remedial measures are not taken, then this may lead to blackout or collapse of the whole system. As a result of a number of voltage stability incidents reported from various countries, there is a widespread interest in understanding, characterizing and preventing this phenomena. This thesis is essentially concerned with analyzing the existing methods and the development of new methods for the assessment of voltage stability of power systems. We examine four existing methods for assessing voltage stability with regard to the computational effort involved in their calculation, the useful information we get by using them, their relative effectiveness in assessing the voltage stability and their consistency in predicting the voltage stability of the system. We also study the impact of the system conditions on several of these indices. Further, we propose a set of new indices which provide information similar to the conventional indices but are slightly different. The generalized circle diagram approach proposed earlier to study the variation of the system variables with respect to the independent node parameters is shown to be adoptable for finding the voltage stability limit of a system. It has been shown that the well known continuation power flow method used for voltage stability analysis is identical to the generalized circle diagram approach. A computationally simple approach, based on the Thevenin equivalent of the power system is used to determine the loadability limit of a system. In the continuation power flow method, it is inherently assumed that only one generator responds to the real power load increase of the system. However, an alternate view is presented where all the generators respond to the real power increase in the system and an algorithm is proposed to realize this condition. Using this algorithm, the generation pattern of the system is modified so as to increase the loadability limit of the system considerably. The origin of the voltage instability in power systems can be traced to the load characteristics. Induction motors constitute a significant proportion of the total industrial and residential loads. Two algorithms that are useful to study the voltage stability of systems having induction machines have been presented and validated. These methods are based on the induction machine static equations. The first method is useful in assessing the impact of network disturbances on voltage stability and the second facilitates the computation of the loadability limit. A criterion has been proposed to find the stability limit, stable and unstable operating regions for a system considering various types of induction motor loads on the basis of which, a practical algorithm is proposed and validated to determine the stability of the induction motors driving different types of loads in a large power system. In addition, a method is developed to determine the stability aspects when the constant torque loads and the constant input power loads driven by induction motors operate in a power system, which contains other types of loads like the constant P - Q type of loads. Switching capacitors at the induction motor terminals is one of the ways by which voltage instability occurring due to the induction motor loads can be prevented. A new technique is proposed wherein knowing the capacitance and the slip at the instant of switching, the rotor dynamics following the switching and the existence of a steady state operating point following the switching can be predicted. This approach can be used to choose appropriate capacitances to be switched at the induction motor terminals to prevent its stalling following a sudden load disturbance.

Several sensor technologies have been developed and experimented over the last few decades to cater various needs of medical diagnostics. Among these, fiber optic sensors, in particular, Fiber Bragg Grating (FBG) based sensors have attracted considerable attention due to their inherent advantages such electrical passiveness, immunity to Electro Magnetic Interference (EMI), chemical inertness, etc. The present research work focuses on design, development and validation of FBG sensor based devices for measurement of certain healthcare parameters in the context of foot function/gait cycle, cardiac and breathing activity, nostril dominance, hand grip/wrist angle force function, etc. The experimental work presented here emphasizes on the effectiveness and competitiveness of the FBG devices developed, in comparison with standard tools such as Accelerometer, Load cell, Electronic Stethoscope, Electromyogram and Dynamometer. In the field of human balance, stability and geriatrics, two independent FBG devices namely, Fiber Bragg Grating based Stability Assessment Device (FBGSAD) and Optical Sensor Ground Reaction Force measurement Platform (OSGRFP) have been designed, developed and experimented for postural stability assessment and gait analysis respectively. The result of these studies have significant implications in understanding of the mechanism of plantar strain distribution, identifying issues in gait cycles, detecting foot function discrepancies, identifying individuals who are susceptible to falls and to qualify subjects for balance and stability. In the field of ergonomic assessment, Fiber Braggs Grating based Hand Grip Device (FBGHGD) is designed and developed for the measurement of hand grip force which helps in the understanding of several important biomechanical aspects such as neuromuscular system function, overall upper-limb strength, vertebral fracture, skeletal muscle function, prediction of disability, incapacity, mortality and bone mass density (forearm, skeletal sites, spine, hip etc.). Further as an extension of this work, the FBGHGD is used for measurement of force generated by the wrist in different positions of the flexion and extension which relates to the wrist muscle activity and its enactment. In the field of cardiac activity monitoring, a novel, in-vivo, non-invasive and portable device named Fiber Bragg Grating based Heart Beat Device (FBGHBD) is developed for the simultaneous measurement of respiratory and cardiac activities. The work involves designing FBGHBD, validating its performance against traditional diagnostic systems like electronic stethoscope, exploration of its clinical relevance and the usage of FBGHBD in studies involving normal persons and patients with myocardial infarction. The unique design of FBGHBD provides critical information such as nascent morphology of cardiac and breathing activity, heart rate variability, heart beat rhythm, etc., which can assist in early clinical diagnosis of many conditions associated to heart and lung malfunctioning. Further, the scope of this work extends towards evaluating several signal processing algorithms and demonstrating a suitable signal processing architecture for real-time extraction of heart beat and respiratory rates along with its nascent morphologies for critical health care application. In the area of breath monitoring, a Nostril Pressure and Temperature Device (NPTD) is designed and developed which aims at simultaneous, accurate and real-time measurement of nostril air flow pressure and temperature to aid in clinical diagnosis of nasal dysfunction and associated nose disorders. The results of NPTD can offer certain vital features like breathing pattern, respiratory rate, changes in individual nostril temperature/pressure, nostrils dominance, body core temperature etc., which can assist in early clinical diagnosis of breathing problems associated with heart, brain and lung malfunctioning. Since the research work in this thesis involve experiments engaging human subjects, necessary approvals from the ethical committee is obtained before the experiments and required ethical procedures are followed during all the experimental trials.