Installation of reactive compensators is widely used for improving power system voltage stability. Reactive compensation also improves the system loading margin resulting in more stable and reliable operation. The improvements in system performance are highly dependent on the location where the reactive compensation is placed in the system. This paper compares three load flow analysis methods - PV curve analysis, QV sensitivity analysis, and Continuation Load Flow - in identifying system weak buses for placing reactive compensation. The methods are applied to three IEEE test systems, including modified IEEE 14-bus system, IEEE 30-bus system, and IEEE 57-bus system. Locations of reactive compensation and corresponding improvements in loading margin and voltages in each test system obtained by the three methods are compared. The author also analyzes the test systems to locate the optimal placement of reactive compensation that yields the maximum loading margin. The results when compared with brute force placement of reactive compensation show the relationship between effectiveness of the three methods and topology of the test systems.

The number of integrated wind farms into the power system is increasing as well as the total installed wind power capacity, which may cause voltage stability concerns. Additionally, there are European Transmission System Operators (TSOs) that do notinvolve wind farms in contributing to the voltage control in any significant extent. In the on-going project by the European Network of Transmission System Operators for Electricity (ENTSO-E), to update the European grid requirements, this will probably be changed. The aim of this Master thesis is to demonstrate the voltage variations in the high voltage grid during different operational conditions. Thereafter, clarify when high voltages may occur at the connection point of the studied wind farm. Furthermore, it is investigated whether the wind farm is able to regulate the voltage in the cases when high voltages occur. The load flow and switching studies are performed with the software tool Power System Simulator for Engineering (PSS/E) version 32.1.1. The grid model represents a part of the Swedish high voltage grid. Since voltage stability often is a local issue, special modelling aspects has been performed at the hydropower generators in the close-located area of the wind farm. The main conclusions of this Master thesis are that high voltages is associated with low load situations, i.e., mostly during summer nights. Furthermore, the studied close-located reactor is not able to keep the voltage within desired level by itself. Finally, it has been shown that the wind farm is technically able to contribute to the voltage stability in the close-located area. But since wind power is an intermittent power source it makes the voltage regulating capacity less reliable compared to hydropower. The results and conclusions given in this Master thesis have also been summarized in a conference paper for The 11th International Workshop on Large-Scale Integration of Wind Power into Power Systems as well as on Transmission Networks for Offshore Wind Power Plants, see Lidström et al [35].

The objective of this thesis is to update the outage management system (OMS) in Taipower by verifying the phasing of distribution transformers and the connectivity of customers served by each distribution transformer. The GPS based phase measurement unit (PMU) is used to measure the voltage phasing of the transformer. The power line carrier (PLC) based identifier has been developed to support the identification of distribution transformer and all the customers served. In the thesis, four practical distribution feeders in Fengshan District of Taipower are selected for the update of distribution transformer phasing of OMS system for the update of distribution transformer phasing of OMS system. After correcting the phasing of distribution transformer in the OMS database, the attributes of distribution components are retrieved for the OMS system. The network configuration of distribution feeders is identified by exacting the topology process and node reduction to prepare the input data for load flow analysis. With the monthly energy consumption of customer from the customer information system (CIS) and the typical load patterns of various customer classes, the hourly loading of each transformer can be derived. By retrieving the actual power data of test feeders from the distribution dispatch control center (DDCC), the three phase load flow analysis is executed to solve the three phase currents of trunk line sections, laterals and distribution transformers. The three phase currents solved can therefore be applied to derive the strategy of three phase balancing of distribution feeders.

This thesis is to investigate the power system operation strategy for an electrified mass rapid transit¡]MRT¡^network with the load transfer among main transformers by considering load growth and due to annual ridership increase, the loading factors of main transformers are improved so that the power system loss can be reduced. For the conventional planning of an electrified MRT system to serve the public transportation for the metropolitan area, the transformer capacity is often designed to meet the criterion of not only covering the peak demand but also providing the 100% fully capacity reserve for the system operation of target year. With such a high backup capability, the transformers are very lightly loaded for most of the operation time and significant core loss will be introduced over the lifecycle. In this thesis the train motion equation has been applied to find the mechanical power required, the proper strategy of unit commitment of main transformers and network reconfiguration by switching operation has been considered to enhance the operation efficiency of an MRT power system. To demonstrate the effectiveness of the proposed methodology, the Taipei MRT network is selected for computer simulation. It is found that the loading factors of main transformers can be improved dramatically and the load balance among the transformers can be obtained by the proper switching operation. An efficient strategy for transformer planning by taking into account the growth rate of load so that the overall investment cost of main transformers can be justified. The load characteristics and load growth rate of mass rapid transit¡]MRT¡^are derived by an Energy Management Model (EMM) and the AC load flow analysis is used to solve the transformer copper loss and core loss over the study period. To obtain optimal planning and operation strategy of main transformers for the MRT power system, the transformers initial investment cost and depreciation cost, peak power loss and energy loss, and reliability cost of distribution transformers are combined to form the overall cost function .By performing the dynamic programming (DP) the unit commitment of main transformers by considering the annual peak and off peak power loading of whole MRT system is derived. It is found that more efficient system operation can be obtained by the proposed methodology.

With increasing level of distributed generation¡]DG¡^on radial feeders in electric distribution systems, it could cause over-voltages as well as under-voltages depending on several factors including DG capacity, locations, and the strategy of voltage regulation. This thesis describes the typical and proposed voltage control strategies that could allow the increase of DG interconnection capacity. By using probabilistic load flow technique, voltage regulation performance for cases with different levels of DG outputs, demands and voltage control strategies are presented. They are compared by using a voltage profile improvement index and a risk assessment technique.

Power losses in the grid are important, and as the power losses decrease the efficiency increases. Not much research has been done recently on the Newton-Raphson Power Flow (NRPF) method in polar form for systems with High Voltage Direct Current (HVDC) subsystems. The point of departure for this thesis is based on decoupling the NR Power Flow method Power flow problems are solved for many fundamental problems in the operation and planning of the power system. Although many methods are available to solve these problems, this thesis focuses on developing an enhanced HVDC power flow method with improved computational efficiency and convergence stability. A comparison of the results with full Newton-Raphson Power Flow method is presented to evaluate the performance of the proposed method. Simulations were conducted on the 14-bus and 30-bus IEEE systems. Two and three converters are shown to improve the voltage magnitude, active and reactive power profile .The overall results indicate which mode is the best mode compared to others depending on the bus importance.

As a special case of the static state estimation problem, the load-flow problem is studied in this thesis. It is demonstrated that the non-linear load-flow formulation may be solved by real-coded genetic algorithms. Due to its global optimisation ability, the proposed method can be useful for off-line studies where multiple solutions are suspected. This thesis presents two methods for estimating the uncertainty interval in power system state estimation due to uncertainty in the measurements. The proposed formulations are based on a parametric approach which takes in account the meter inaccuracies. A nonlinear and a linear formulation are proposed to estimate the tightest possible upper and lower bounds on the states. The uncertainty analysis, in power system state estimation, is also extended to other physical quantities such as the network parameters. The uncertainty is then assumed to be present in both measurements and network parameters. To find the tightest possible upper and lower bounds of any state variable, the problem is solved by a Sequential Quadratic Programming (SQP) technique. A new robust estimator based on the concept of uncertainty in the measurements is developed here. This estimator is known as Maximum Constraints Satisfaction (MCS). Robustness and performance of the proposed estimator is analysed via simulation of simple regression examples, D.C. and A.C. power system models.

As perdas técnicas e comerciais apresentam valores significativos nas empresas de distribuição de energia elétrica, prejudicando o seu desempenho técnico e financeiro. A aplicação e avaliação das técnicas de redução de perdas estão diretamente relacionadas à correta estimação das mesmas. Este trabalho tem o objetivo de analisar o desempenho dos métodos baseados em fluxo de carga e estimação de estados na estimação de perdas, considerando sistemas de distribuição equilibrados. O método de fluxo de carga utilizado é o Newton-Raphson. Considerando este fluxo de carga, os métodos de comparação com medições e de fatores de correção são descritos e aplicados, ambos revisados da literatura. Utilizando o estimador de estados por mínimos quadrados ponderados, a estimação das perdas é dada com o auxílio da análise de erros grosseiros. Nos métodos utilizados, o primeiro aplica a análise dos resíduos, conforme é apresentado na literatura, no outro método, é proposta a aplicação da análise dos erros compostos. O estudo de caso é realizado em um sistema de distribuição equilibrado, considerando predições de carga e um número restrito de medições. Nos casos propostos, são inseridos diferentes níveis de perdas comerciais, em diferentes barras, e é considerado que as predições de carga e as medições estão sujeitas a erros. Para cada caso proposto, os resultados apresentam os erros dos métodos na estimação das perdas técnicas e comerciais. Adicionalmente, é realizada uma análise da relação dos erros com o nível de inserção de perdas comerciais. O trabalho também apresenta o desempenho dos métodos na localização das perdas comerciais e um estudo do custo computacional das metodologias. Os resultados demonstram que a precisão da predição de carga é determinante na estimação das perdas comerciais. O método baseado em estimador de estados com a aplicação da análise de erros compostos, proposto neste trabalho, apresentou os melhores resultados na estimação e identificação de perdas. A expansão deste método para sistemas de distribuição maiores e desequilibrados aparenta ser uma alternativa interessante para a estimação e combate de perdas. / The technical and commercial energy losses are significant in distribution companies, hampering the technical and financial performance. The application and evaluation of techniques to reduce losses are directly related to the proper loss estimation. This work aims to analyze the performance of loss estimation using methods based on load flow and state estimation, considering balanced distribution systems. The method of load flow used is the Newton-Raphson. Considering this load flow, the methods of comparison with measurements and correction factors are described, both of them from the literature. Using the weighted least squares state estimator, the losses are estimated using the gross error analysis. One of the methods uses the residue analysis, as presented in the literature, in another method, is proposed to use the composed error analysis. The case study is performed in a balanced distribution system, considering load forecastings and a limited number of measurements. In the proposed cases, different levels of commercial losses are inserted in different buses, and it is considered that load forecatings and measurements are subject to error. For each proposed case, the results show the methods errors in technical and commercial loss estimation. Additionally, an analysis of the relationship of estimation errors with the level of commercial losses is performed. This work also shows the methods performance in the commercial losses location and a study of the computational costs of methods. The results show that the load forecast accuracy is relevant in the commercial losses estimation. The method based on state estimation that uses composed error analysis, proposed in this dissertation, showed the best results in the loss estimation and identification. The expansion of this method for larger and unbalanced distribution systems appears to be an interesting alternative to estimate and combat losses.

This thesis considers three separate but connected problems regarding energy networks: the load flow problem, the optimal power flow problem, and the islanding problem. All three problems are non-convex non linear problems, and so have the potential of returning local solutions. The goal of this thesis is to find solution methods to each of these problems that will minimize the chances of returning a local solution. The thesis first considers the load ow problem and looks into a novel approach to solving load flows, the Holomorphic Embedding Load Flow Method (HELM). The current literature does not provide any HELM models that can accurately handle general power networks containing PV and PQ buses of realistic sizes. This thesis expands upon previous work to present models of HELM capable of solving general networks efficiently, with computational results for the standard IEEE test cases provided for comparison. The thesis next considers the optimal power flow problem, and creates a framework for a load flow-based OPF solver. The OPF solver is designed with incorporating HELM as the load flow solver in mind, and is tested on IEEE test cases to compare it with other available OPF solvers. The OPF solvers are also tested with modified test cases known to have local solutions to show how a LF-OPF solver using HELM is more likely to find the global optimal solution than the other available OPF solvers. The thesis finally investigates solving a full AC-islanding problem, which can be considered as an extension of the transmission switching problem, using a standard MINLP solver and comparing the results to solutions obtained from approximations to the AC problem. Analysing in detail the results of the AC-islanding problem, alterations are made to the standard MINLP solver to allow better results to be obtained, all the while considering the trade-off between results and elapsed time.

As perdas elétricas, que no Brasil giram em torno de 14,4%, são prejudiciais ao desempenho técnico e financeiro das concessionárias de energia elétrica, principalmente em um cenário de uma eminente crise energética e alta regulação. A mitigação das perdas elétricas está diretamente relacionada com sua correta estimação. Para operar um sistema de energia elétrica, é de fundamental importância definir a correta modelagem dos elementos do sistema. As metodologias de estimação das perdas de energia, para sistemas de distribuição, vigentes não levam em conta possíveis erros na correta modelagem das cargas conectadas. Desta forma, este trabalho tem o objetivo de analisar a influência causada pela utilização dos modelos de carga, na estimação das perdas elétricas em sistemas de distribuição. Esta análise abrange as metodologias de fluxo de carga backward-forward sweep por soma de corrente, por soma de potência e Newton-Raphson. A perda de energia é calculada pela diferença entre a energia injetada no sistema, menos a energia entregue. O estudo de caso é realizado em um sistema de distribuição teste de 13 barras da IEEE. No caso proposto, são realizados cálculos das perdas de energia para o sistema de distribuição, considerando diferentes modelos de carga. Desta maneira, o trabalho estimou a diferença no cálculo das perdas para cada tipo de modelo de carga, em relação a perdas calculadas com o padrão original das cargas. Outro ponto analisado foi o desempenho das metodologias de fluxo de carga, frente à alteração dos modelos de carga. Os resultados demonstram que a alteração dos modelos de carga influência a estimação das perdas elétricas nos sistemas de distribuição, e o desempenho dos fluxos de carga. / Electrical losses, which in Brazil are around 14.4%, are harmful to the technical and financial performance of electric utilities, especially in a scenario of an imminent energy crisis and high regulation. Mitigation of electrical losses is directly related to its correct estimation. To operate an electric power system, it is of fundamental importance to define the correct model of the system elements. The methodologies for estimating energy losses, for the existing distribution systems, do not take into account possible errors in the correct model of connected loads. Thus, this study aims to examine the influence caused by the use of different load models, in the estimation of electrical losses in distribution systems. This analysis covers the backward-forward sweep load flow methodologies by the sum of current, by the sum of power and Newton-Raphson. The energy loss is calculated by the difference between the energy injected into the system, minus the energy delivered. The case study is performed on the IEEE 13 Node Test Feeder. In the proposed case, calculations of energy losses in the distribution system are performed considering different load models. Therefore, the study has estimated the difference in the calculation of energy loss for each type of load model, for the losses calculated with the original pattern of loads. Another point discussed is the performance of load flow methodologies, related to the change of load models. The results have shown that the change in load models influence the estimation of electrical losses in distribution systems and in the performance of load flows.