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Electric power systems are characterized by their immense complexity. The assessment of their security on-line has always been a challenging task. Many possibilities were investigated in the past in an attempt to characterize the secure operating region of a power system. Pattern recognition is thus far the only tool that can take various degrees of network complexity into consideration. / In the present study, an efficient algorithm which learns adaptively the secure operating region is proposed. At each iteration, training operating points are generated sequentially on a piecewise linearly approximated separation surface computed by the one-nearest-neighbor (1-NN) rule. The separation surface so estimated approaches the true one as the number of training points increases. The algorithm not only provides a consistent technique in learning an unknown region, it generates a highly efficient training set. It is found to be effective in reducing the size of the training set without adverse effect to the classifier. / Once the secure region of a power system is available, the task of on-line security monitoring reduces to one of determining whether the current operating point resides in the secure region. As demonstrated in the thesis, both the security status and the security margin of the operating point can be assessed very efficiently. By using the piecewise linearly approximated secure region, the thesis proceeds to give efficient ways of moving an insecure operating point into the secure region. This comprises the problem of security enhancement. / The regionwise methodology via the Voronoi diagram developed in the thesis is also applied to a wide range of problems, such as network planning, coordinating tuning of machine parameters and automatic contingency selection. The major merit is that the dynamics and the nonlinearity of the system no longer present a limitation to solving these problems.

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

Thesis (M.S.)--Drexel University, 2008. / Includes abstract. Includes bibliographical references (leaves 81-83).

Thesis (M.S.)--Ohio University, August, 2006. / Title from PDF t.p. Includes bibliographical references.

Thesis (M.S. in electrical engineering)--Washington State University, December 2007. / Includes bibliographical references (p. 61-62).

Thesis (Ph. D.)--University of Wyoming, 2005. / Title from PDF title page (viewed on Oct. 16, 2007). Includes bibliographical references (p. 117-120).

Dissertation (Ph.D.)--Auburn University, 2006. / Abstract. Vita. Includes bibliographic references.

Thesis (M.S.)--Ohio University, November, 1998. / Title from PDF t.p.