The analysis and characterization of the steady-state security of a bulk-power electric system is investigated in a region-wise or set-theoretic framework. The study is divided into three parts: a detailed examination of the theoretical aspects of general security regions; a formulation and analysis of the problem of characterizing a set of secure operating points by a simple, explicit function; and an investigation into the secure loadability of a power system. Based on the results of the theoretical study, general approximate relations expressing dependent load flow variables in terms of the nodal injections are derived. Their degree of accuracy and extent of validity are investigated through analytical and simulation-based analyses. The general problem of characterizing subsets of a security region by simple, explicit functions is formulated as an optimization problem. For the case where the subsets are expressed by ellipsoids, two algorithms are developed and tested. The problem is then extended to include embedding the largest ellipsoid of a £ixed orientation inside a security region. The application of explicit security sets to the problem of predictive security assessment is studied in detail. A number of explicit security subsets overlapping along the predicted daily trajectory is used to define a "security corridor". This predicted corridor has the property that as long as the actual trajectory stays within it, very little computation is needed to assess the system security. The secure loadability of a power system is first studied in the demand space by considering the orthogonal projection of security sets into that space. It is then studied in the voltage space in the context of existence of a secure load flow solution to a given loading condition. Properties of the set of secure voltage solutions are explored by enclosing it with a linear set. Furthermore, it is shown that, under favorable conditions, one can easily characterize a subset of the set / L'analyse et la caracterisation de la securite en regime permanent pour un reseau et transmission ont ete etudiees dans le contexte de la theorie des ensembles. L'etude est divisee en trois parties: un examen detaille: des aspects theoriques des regions de securite generale; la formulation et l'analyse de probleme de la caracterisation d'un ensemble de points de fonctionnement par une fonction simple, sous forme explicite, et l'etude de la capacite de charge d'un reseau. Une analyse theorique a permis de deriver des relations approximative generales, exprimant les variables dependantes de l'ecoulement de puissance en terme des injections de noeud. Le degre de precision de ces approximations ainsi que leurs limites d'application sont determinees a l'aide de simulations et d'analyses theoriques. Le probleme general de la caracterisation des sous-ensembles d'une region de securite par des fonctions simples et sous forme explicite est formule comme probleme d'optimisation. Dans le cas ou les sous-ensembles sont exprimes par des ellipsoides, deux algorithmes sont developpes et verifies. Le probleme est alors elargi de facon a inclure le plus grand ellipsoide d'orientation fixe a l'interieur d'une region de securite. L'application d'ensembles de securite au prob1eme de l'evaluation preventive est etudiee en detail. On utilise un certain nombre d'ensembles de securite se recoupant long de la trajectoire journaliere prevue de facon a definir un corridor de securite. Ce corridor prevu possede la propriete qu'aussi longtemps que la trajectoire y est confinee, un minimum de calculs est requis pour evaluer la securite du systeme. Le chargement securitaire d'un reseau est en premier lieu etudie en considerant la projection orthogonale des ensembles de securite sur cet espace. Il est ensuite etudie dans l'espace des tensions, dans le contexte de l'existence d'une solution pour une charge donnee. Les proprietes de l'ensemble des solutions securitaires sont explorees en l'enchas

M.Ing. (Electrical and Electronic Engineering) / Shunt reactors are used in power system amongst other things, to suppress overvoltages in the network during network switching, auto reclosing of transmission lines and under low loading condition of the network. Traditionally, shunt reactors of fixed type have been used and these have been permanently connected to the system. This research work investigated the feasibility of replacing the fixed shunt line reactors with a reactor, whose parameters are automatically varied depending on the system reactive power requirements, in a mature power system overlaid with high voltage lines to improve amongst, other things voltage stability. However, in a mature system overlaid with parallel higher voltage lines, power tend to flow on the matured system rather than higher voltage system as predetermined by various impedances of the power system. It is therefore desirable that loading of higher voltage lines be increased because of their higher power transfer capability and fact that higher voltage networks generate capacitive power which is substantially more than for each line at the original voltage. However, replacing a large number of fixed line reactors, at low loadings of higher voltage lines, even when system collapse is averted by increasing the number of reactors inserted into the system, overvoltage problems may still be an issue, until a certain number of must-run reactors, operating at full reactance, are put into service. If too much inductive reactance is removed from the system when the loading levels are extremely low, the power system will collapse. Therefore, there was no economic benefit in replacing all the fixed shunt line reactors with controllable type when the loading was still relatively low. Thus, the majority of the converted reactors were operating in their full rating as there was still more reactive power to be absorbed. However, when the power was diverted to flow on the higher voltage system through the use of series compensation of the higher voltage system, there was a possibility of making some fixed shunt line reactors on the higher voltage network controllable. This also allowed more power to be transferred in the higher voltage system thus improving its utilisation. Also, a positive impact on active system losses was realised.

Transient stability analysis is an important part of power planning and operation. For large power systems, such analysis is very time consuming and expensive. Therefore, an online transient stability assessment will be required as these large power systems are operated close to their maximum limits. In this thesis swallowtail catastrophe is used to determine the transient stability regions. The bifurcation set represents the transient stability region in terms of power system transient parameters bounded by the transient stability limits. The system modelling is generalized in such, that the analysis could handle either one or any number of critical machines. This generalized model is then tested on a three-machine as well as a seven-machine system. The results of the stability analysis done with the generalized method is compared with the time solution and the results were satisfactory. The transient stability regions determined are valid for any changes in loading conditions and fault location. This method is a good candidate for on-line assessment of transient stability of power systems. / Applied Science, Faculty of / Electrical and Computer Engineering, Department of / Graduate

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Thesis (MScIng)--University of Stellenbosch, 2004. / ENGLISH ABSTRACT: Electricity theft in South Africa has become a major problem. This led to several developments from both industries and research institutes to counter these actions. Since equipment is already installed and major capital has been invested to provide electricity for a broad spectrum of consumers, the challenge is to find a low cost solution harnessing current investments and technology to detect electricity theft more accurately. This thesis investigates into the electricity theft topic. Two different methods, Time Domain Pulse Reflectometry and a data driven platform based on the Theory of Constraints philosophy, were investigated to provide means to detect and determine the impact of illegal electricity usage. Both methods required detailed designs to conduct preliminary proof of concept tests in a laboratory environment. These methods are evaluated against their economical viability, possible practical implications and applications. This thesis presents a practical approach to electricity theft detection and provides the basic tools for management of this ever-increasing problem. / AFRIKAANSE OPSOMMING: Suid Afrika se elektrisiteit diefstal statistiek het die afgelope jare skrikwekkend gegroei. Dit het die industrie genoop om baie meer navorsing in die area te doen. Met reeds gevestigde toerusting en tegnologie om di´e energie medium so effektief moontlik te versprei, is die uitdaging juis om ’n ekonomiese oplossing te vind om reeds beskikbare tegnologie¨e meer doeltreffend aan te wend. Die doel van die tesis is om die gebied van elektrisiteit diefstal na te vors. Twee verskillende metodes is ondersoek, naamlik Tydgebied-pulse-reflektometrie en ’n informasie gebaseerde stelsel wat op die Randvoorwaarde Teorie gebaseer is, om effektief die omvang van elektrisiteit diefstal in ’n mikro, asook makro omgewing te bepaal. Die twee metodes is in ’n beheerde omgewing getoets sodat die konsepte wat ontwikkel is bewys kon word. Die metodes is ge-evalueer in terme van die ekonomiese lewensvatbaarheid daarvan met inagneming van die praktiese implikasies. Die tesis bied bestuur die nodige kennis om elektrisiteit diefstal in die praktyk doeltreffend die hok mee te slaan.

A project report submitted to the Faculty of Engineering, University of the Witwatersrand, in partial fulfilment of the requirements for the degree of Master of Science in Engineering. Johannesburg 1995. / Advances in digital computing technology make it possible to improve the design of the Man Machine Interface (MMI), SCADA and ALARM modules used in electrical utility control centres. to overcome the problem of control staff data overloading. A possible solution is proposed, based on-an explicit representation of a disturbed power system state in addition to quiescent conditions. The structure of modem SCADA, installations is analysed in terms of the computing power of full graphic workstations, the quantities of element data delivered to the control room and the capabilities of intelligent remote terminal units. This analysis indicates that existing designs for the presentation of SCADA data need to change to solve the data overloading-problem. The proposed philosophy moves the focus of attention from the element level up to the device level by grouping and dividing all elements into categories at the RTU and linking them to their parent device, Control staff are notified graphically on the one-line displays, next to the device in question, of the existence of abnormal elements by category. The element state details for the device are only displayed on demand, resulting in a 95% reduction of alarm text messages. Suggestions are made as to the software functions needed at tbe RTU and the workstation to assist with the display of system data. Lastly racommendations are offered to reduce maintenance by standardising and pre-ordering device element data. / AC2017

by Kin Kwong Leung. / Thesis submitted in: November 1999. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2000. / Includes bibliographical references (leaves 67-[70]). / Abstracts in English and Chinese. / Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- Code Division Multiple Access (CDMA) --- p.1 / Chapter 1.1.1 --- The Cellular Concept --- p.2 / Chapter 1.2 --- Fading and Power Control --- p.3 / Chapter 1.2.1 --- Large Scale Fading --- p.3 / Chapter 1.2.2 --- Small Scale Fading --- p.4 / Chapter 1.2.3 --- Power Control --- p.5 / Chapter 1.2.4 --- Standard Interference Function --- p.5 / Chapter 1.3 --- Previous Work --- p.6 / Chapter 1.3.1 --- Power Control --- p.6 / Chapter 1.3.2 --- Convergence Analysis --- p.8 / Chapter 1.4 --- Scope of this Thesis --- p.8 / Chapter 1.5 --- Organization of the Thesis --- p.9 / Chapter 2 --- System Model --- p.10 / Chapter 2.1 --- System and Definitions --- p.10 / Chapter 2.2 --- Varying Link Gains Model --- p.11 / Chapter 2.3 --- SIR model in CDMA System --- p.13 / Chapter 2.4 --- Simulation Model --- p.14 / Chapter 3 --- Fade Margin --- p.17 / Chapter 3.1 --- Introduction --- p.17 / Chapter 3.2 --- Fixed-step Power Control Algorithm --- p.18 / Chapter 3.3 --- Definitions and Feasibility of SIR --- p.19 / Chapter 3.3.1 --- Definition --- p.19 / Chapter 3.3.2 --- Feasibility --- p.20 / Chapter 3.4 --- Performance Analysis on Fading Channel --- p.22 / Chapter 3.4.1 --- Single-User --- p.22 / Chapter 3.4.2 --- Multiple-User --- p.24 / Chapter 4 --- Generalized Step Power Control Algorithm --- p.28 / Chapter 4.1 --- Introduction --- p.28 / Chapter 4.2 --- Generalized Fixed Step Power Control Algorithm --- p.29 / Chapter 4.3 --- Existence of the Solution --- p.30 / Chapter 4.4 --- Parameter Optimization --- p.31 / Chapter 4.4.1 --- Single-User --- p.34 / Chapter 4.4.2 --- Multiple-User --- p.37 / Chapter 4.5 --- Performance Analysis --- p.41 / Chapter 4.5.1 --- Single-User --- p.41 / Chapter 4.5.2 --- Multiple-User --- p.42 / Chapter 4.6 --- Hybrid Scheme --- p.47 / Chapter 5 --- Convergence Analysis --- p.49 / Chapter 5.1 --- Introduction --- p.49 / Chapter 5.2 --- Totally Asynchronous Models --- p.50 / Chapter 5.3 --- Normalized Interference Function --- p.52 / Chapter 5.4 --- Existence of Quantized Solution --- p.53 / Chapter 5.5 --- Convergence Theorem --- p.55 / Chapter 6 --- Conclusion and Future Work --- p.64 / Chapter 6.1 --- Conclusion --- p.64 / Chapter 6.2 --- Future Works --- p.65 / Bibliography --- p.67

Extensive studies have been undertaken on the transient stability of large interconnected power systems with flexible ac transmission systems (FACTS) devices installed. Varieties of control methodologies have been proposed to stabilize the postfault system which would otherwise eventually lose stability without a proper control. Generally speaking, regular transient stability is well understood, but the mechanism of load-driven voltage instability or voltage collapse has not been well understood. The interaction of generator dynamics and load dynamics makes synthesis of stabilizing controllers even more challenging. There is currently increasing interest in the research of neural networks as identifiers and controllers for dealing with dynamic time-varying nonlinear systems. This study focuses on the development of novel artificial neural network architectures for identification and control with application to dynamic electric power systems so that the stability of the interconnected power systems, following large disturbances, and/or with the inclusion of uncertain loads, can be largely enhanced, and stable operations are guaranteed. The latitudinal neural network architecture is proposed for the purpose of system identification. It may be used for identification of nonlinear static/dynamic loads, which can be further used for static/dynamic voltage stability analysis. The properties associated with this architecture are investigated. A neural network methodology is proposed for dealing with load modeling and voltage stability analysis. Based on the neural network models of loads, voltage stability analysis evolves, and modal analysis is performed. Simulation results are also provided. The transient stability problem is studied with consideration of load effects. The hierarchical neural control scheme is developed. Trajectory-following policy is used so that the hierarchical neural controller performs as almost well for non-nominal cases as they do for the nominal cases. The adaptive hierarchical neural control scheme is also proposed to deal with the time-varying nature of loads. Further, adaptive neural control, which is based on the on-line updating of the weights and biases of the neural networks, is studied. Simulations provided on the faulted power systems with unknown loads suggest that the proposed adaptive hierarchical neural control schemes should be useful for practical power applications. / Graduation date: 1999