Transformers are essential components facilitating transmission and distribution of electric power. Energisation of transformers, however, can cause core operating at deep saturation region and thereby induce transient inrush currents of high magnitude and with rich harmonics. This can lead to undesirable effects including potential damage to the transformer itself, relay mal-operation, harmonic resonant overvoltages, and reduced power quality in the system (mainly in the form of voltage dips). This thesis investigates voltage dips caused by energising generator step-up (GSU) transformers and two types of generation connection are studied: one is a combine cycle gas turbine (CCGT) plant connected to a 400 kV transmission grid and the other is a large offshore wind farm connected to a 132 kV distribution grid. To carry out the investigation, detailed network models were developed in alternative transients program/electromagnetic transients program (ATP/EMTP) and validated with the help of field measurements. For the connection of generation in the transmission grid, deterministic assessment was conducted to comparatively analyse voltage dips caused by energising large GSU transformers under different energisation conditions and different network conditions; special attention was paid to the energisation cases involving sympathetic inrush between transformers by addressing its prolonging effects on voltage dips, with sensitivity studies further carried out to identify the key influential parameters. In addition, stochastic assessment was conducted by applying Monte Carlo method, which helps identify the dip frequency pattern and the likelihood of reaching the dip magnitude resulted from the commonly agreed worst case energisation condition; their sensitivities to the variation of circuit breaker closing time span, transformer core residual flux, system condition and the number of transformers being energized together were also investigated. Furthermore, possible cost-effective operational approaches to mitigate the voltage dips were explored and compared. For the connection of large offshore wind farm, voltage dips caused by energising wind turbine transformers under different scenarios were assessed; in particular, sympathetic inrush between wind turbine transformers were studied, and the energisation sequence resulting in less sympathetic inrush was deterministically identified and stochastically validated. The simulation results of deterministic studies indicate that, when carrying out energisation of a large GSU transformer in the transmission grid under the commonly agreed worst case energisation condition, the dip magnitude can reach 9.6% and the duration 2.7 seconds; moreover, when coupled with sympathetic inrush, the duration can be prolonged by 136%, lasting for 6.4 seconds. The sensitivity studies show that transformer core saturation inductance is the key parameter determining dip magnitude and transformer copper losses is the key parameter determining dip duration. Stochastic assessment of voltage dips shows that, out of 1000 stochastic dip events, less than 0.5% of the dips can reach the worst case dip magnitude and about 80% are of magnitudes less than 0.6 pu of the worst case dip magnitude; the dip frequency pattern is found to be insensitive to the circuit breaker closing time variation but can be considerably influenced by the residual flux distribution. In terms of mitigation measures, it was proven that, by adjusting tap changer position, applying static var compensator and even opening coupler circuit breaker in the substation, the degree of voltage dip especially the dip duration can be significantly reduced. Contrasting to those observed in the transmission grid, voltage dips resulted from energising wind turbine transformers in large offshore wind farms are of less concern; dip magnitudes are no more than 1% in the case of energising a stand-alone wind turbine transformer. However, sympathetic inrush between wind turbine transformers within one feeder was found to be significant and the energisation sequence resulting in less sympathetic inrush is to separately energise the wind turbine transformer from the one closest to the offshore platform to the one farthest away from the platform.

Student Number : 0004041J - MSc dissertation - School of Electrical and Information Engineering - Faculty of Engineering / Slip energy recovery (SER) drives are used extensively in industry as they offer cost effective speed control of large wound rotor induction motors. The biggest disadvantage associated with the use of SER drives is the vulnerability of the rotor circuit converters to power system disturbances such as voltage dips. The failure of converters as a result of voltage dips is a problem associated with the use of these particular drives. The aim of this research is to better understand the stresses on rotor circuit converters as a result of voltage dips at the terminals of the motor. The rotor transients developed by a wound rotor induction motor are investigated for a range of three phase and single phase voltage dips. Simulations conducted in the Alternative Transients Program (ATP) supplement measurements conducted on a simplified SER circuit. The results confirm that voltage dips cause significant stresses on the converters in the rotor circuit. Good correlation was obtained between simulated and measured results. This work allows for a better understanding of the response of wound rotor induction motors to voltage dips and identifies the threat that voltage dips impose on the SER rotor circuit converters.

Developments in measurement technology, communication and data storage have resulted in measurement systems that produce large amount of data. Together with the long existing need for characterizing the performance of the power system this has resulted in demand for automatic and efficient information-extraction methods. The objective of the research work presented in this thesis was therefore to develop new robust methods that extract additional information from voltage and current measurements in power systems. This work has contributed to two specific areas of interest.The first part of the work has been the development of a measurement method that gives information how voltage flicker propagates (with respect to a monitoring point) and how to trace a flicker source. As part of this work the quantity of flicker power has been defined and integrated in a perceptionally relevant measurement method. The method has been validated by theoretical analysis, by simulations, and by two field tests (at low-voltage and at 130-kV level) with results that matched the theory. The conclusion of this part of the work is that flicker power can be used for efficient tracing of a flicker source and to determine how flicker propagates.The second part of the work has been the development of a voltage disturbance classification system based on the statistical learning theory-based Support Vector Machine method. The classification system shows always high classification accuracy when training data and test data originate from the same source. High classification accuracy is also obtained when training data originate from one power network and test data from another. The classification system shows, however, lower performance when training data is synthetic and test data originate from real power networks. It was concluded that it is possible to develop a classification system based on the Support Vector Machine method with “global settings” that can be used at any location without the need to retrain. The conclusion is that the proposed classification system works well and shows sufficiently high classification accuracy when trained on data that originate from real disturbances. However, more research activities are needed in order to generate synthetic data that have statistical characteristics close enough to real disturbances to replace actual recordings as training data.

A inserção de fontes de geração distribuída (GD) traz a possibilidade de diversificação da matriz energética e a redução de perdas elétricas no transporte de EE – porque as fontes localizam-se próximas aos clientes finais. Entre elas destacam-se as fontes fotovoltaicas, eólicas, pequenas centrais hidrelétricas (PCH) e termelétricas à biomassa. As duas primeiras, apresentam a peculiaridade de normalmente serem conectadas à rede através de inversores de frequência. As outras duas costumam ser conectadas diretamente ao sistema. Todavia, a GD também propicia consequências ao SEP, muitas vezes indesejadas, como variações nos parâmetros da qualidade da energia elétrica (QEE). O compromisso que se deve manter com a QEE entregue aos consumidores é de vital importância para as empresas transmissoras e distribuidoras de energia elétrica, bem como para os utilitários dessa EE. Além disso, para que haja o correto funcionamento de equipamentos eletrônicos e de diversos processos industriais é necessário que a energia elétrica permaneça em uma faixa de tensão aceitável. Entre os fenômenos de interesse da área de qualidade de energia elétrica, os quais devem ser eliminados ou mitigados para a melhor operabilidade do SIN, pode-se citar: harmônicos, flutuação de tensão, subtensão, sobretensão e afundamentos de tensão. Devido a observabilidade rotineira e aos prejuízos (financeiros e/ou técnicos) associados ao fenômeno, o interesse desse estudo consiste nos afundamentos de tensão. Nesse contexto, apresenta-se uma proposta para análise dos afundamentos de tensão em um ambiente com geração distribuída (fotovoltaica, eólica, PCH e termelétrica à biomassa) através de simulações de curtos-circuitos. Os resultados obtidos através da metodologia proposta mostram que a inserção de GD pode trazer uma variação no número de afundamentos de tensão e melhorar os níveis de tensão nas barras, sobretudo nos locais onde foram inseridas bem como em suas proximidades. Também, há redução no número de afundamentos de maior severidade os quais causam mais prejuízos e preocupação a operabilidade do SEP. / The insertion of distributed generation (DG) sources brings the possibility of diversification of energy sources types and the reduction of electrical losses in the transport of EE - because the sources are located close to end users. Among these sources are photovoltaic, wind, small hydropower and biomass-fired power plants. The first two, are usually connected to the network through frequency inverters. The other two are usually connected directly to the system. However, DG also provides consequences to the electrical power system, often unwanted, such as variations in the parameters of power quality (PQ). The commitment should be retained with the power quality delivered to customers. Moreover, for the correct operation of electronic equipment and various industrial processes it is necessary that the voltage remains within an acceptable range. Among the phenomena of interest to electric power quality, which must be eliminated or mitigated, we can mention: harmonics, voltage fluctuation, undervoltage, overvoltage and voltage sags (dips). Due to losses (financial and/or technical) associated with the phenomenon, the interest of this study consists of the voltage sags. In this context, we present a proposal for analysis of voltage sags in an environment with distributed generation (photovoltaic, wind, thermal and biomass-fired power plants) through simulations of short circuits. The results obtained through the proposed methodology shows that the inclusion of DG can bring a change in the number of voltage sags and improve voltage levels in bars, especially in places where they were inserted and in its vicinity. Also, there is a reduction in the number of severe voltage sags which cause more harm and concern to end-users and utilities.

A inserção de fontes de geração distribuída (GD) traz a possibilidade de diversificação da matriz energética e a redução de perdas elétricas no transporte de EE – porque as fontes localizam-se próximas aos clientes finais. Entre elas destacam-se as fontes fotovoltaicas, eólicas, pequenas centrais hidrelétricas (PCH) e termelétricas à biomassa. As duas primeiras, apresentam a peculiaridade de normalmente serem conectadas à rede através de inversores de frequência. As outras duas costumam ser conectadas diretamente ao sistema. Todavia, a GD também propicia consequências ao SEP, muitas vezes indesejadas, como variações nos parâmetros da qualidade da energia elétrica (QEE). O compromisso que se deve manter com a QEE entregue aos consumidores é de vital importância para as empresas transmissoras e distribuidoras de energia elétrica, bem como para os utilitários dessa EE. Além disso, para que haja o correto funcionamento de equipamentos eletrônicos e de diversos processos industriais é necessário que a energia elétrica permaneça em uma faixa de tensão aceitável. Entre os fenômenos de interesse da área de qualidade de energia elétrica, os quais devem ser eliminados ou mitigados para a melhor operabilidade do SIN, pode-se citar: harmônicos, flutuação de tensão, subtensão, sobretensão e afundamentos de tensão. Devido a observabilidade rotineira e aos prejuízos (financeiros e/ou técnicos) associados ao fenômeno, o interesse desse estudo consiste nos afundamentos de tensão. Nesse contexto, apresenta-se uma proposta para análise dos afundamentos de tensão em um ambiente com geração distribuída (fotovoltaica, eólica, PCH e termelétrica à biomassa) através de simulações de curtos-circuitos. Os resultados obtidos através da metodologia proposta mostram que a inserção de GD pode trazer uma variação no número de afundamentos de tensão e melhorar os níveis de tensão nas barras, sobretudo nos locais onde foram inseridas bem como em suas proximidades. Também, há redução no número de afundamentos de maior severidade os quais causam mais prejuízos e preocupação a operabilidade do SEP. / The insertion of distributed generation (DG) sources brings the possibility of diversification of energy sources types and the reduction of electrical losses in the transport of EE - because the sources are located close to end users. Among these sources are photovoltaic, wind, small hydropower and biomass-fired power plants. The first two, are usually connected to the network through frequency inverters. The other two are usually connected directly to the system. However, DG also provides consequences to the electrical power system, often unwanted, such as variations in the parameters of power quality (PQ). The commitment should be retained with the power quality delivered to customers. Moreover, for the correct operation of electronic equipment and various industrial processes it is necessary that the voltage remains within an acceptable range. Among the phenomena of interest to electric power quality, which must be eliminated or mitigated, we can mention: harmonics, voltage fluctuation, undervoltage, overvoltage and voltage sags (dips). Due to losses (financial and/or technical) associated with the phenomenon, the interest of this study consists of the voltage sags. In this context, we present a proposal for analysis of voltage sags in an environment with distributed generation (photovoltaic, wind, thermal and biomass-fired power plants) through simulations of short circuits. The results obtained through the proposed methodology shows that the inclusion of DG can bring a change in the number of voltage sags and improve voltage levels in bars, especially in places where they were inserted and in its vicinity. Also, there is a reduction in the number of severe voltage sags which cause more harm and concern to end-users and utilities.

A inserção de fontes de geração distribuída (GD) traz a possibilidade de diversificação da matriz energética e a redução de perdas elétricas no transporte de EE – porque as fontes localizam-se próximas aos clientes finais. Entre elas destacam-se as fontes fotovoltaicas, eólicas, pequenas centrais hidrelétricas (PCH) e termelétricas à biomassa. As duas primeiras, apresentam a peculiaridade de normalmente serem conectadas à rede através de inversores de frequência. As outras duas costumam ser conectadas diretamente ao sistema. Todavia, a GD também propicia consequências ao SEP, muitas vezes indesejadas, como variações nos parâmetros da qualidade da energia elétrica (QEE). O compromisso que se deve manter com a QEE entregue aos consumidores é de vital importância para as empresas transmissoras e distribuidoras de energia elétrica, bem como para os utilitários dessa EE. Além disso, para que haja o correto funcionamento de equipamentos eletrônicos e de diversos processos industriais é necessário que a energia elétrica permaneça em uma faixa de tensão aceitável. Entre os fenômenos de interesse da área de qualidade de energia elétrica, os quais devem ser eliminados ou mitigados para a melhor operabilidade do SIN, pode-se citar: harmônicos, flutuação de tensão, subtensão, sobretensão e afundamentos de tensão. Devido a observabilidade rotineira e aos prejuízos (financeiros e/ou técnicos) associados ao fenômeno, o interesse desse estudo consiste nos afundamentos de tensão. Nesse contexto, apresenta-se uma proposta para análise dos afundamentos de tensão em um ambiente com geração distribuída (fotovoltaica, eólica, PCH e termelétrica à biomassa) através de simulações de curtos-circuitos. Os resultados obtidos através da metodologia proposta mostram que a inserção de GD pode trazer uma variação no número de afundamentos de tensão e melhorar os níveis de tensão nas barras, sobretudo nos locais onde foram inseridas bem como em suas proximidades. Também, há redução no número de afundamentos de maior severidade os quais causam mais prejuízos e preocupação a operabilidade do SEP. / The insertion of distributed generation (DG) sources brings the possibility of diversification of energy sources types and the reduction of electrical losses in the transport of EE - because the sources are located close to end users. Among these sources are photovoltaic, wind, small hydropower and biomass-fired power plants. The first two, are usually connected to the network through frequency inverters. The other two are usually connected directly to the system. However, DG also provides consequences to the electrical power system, often unwanted, such as variations in the parameters of power quality (PQ). The commitment should be retained with the power quality delivered to customers. Moreover, for the correct operation of electronic equipment and various industrial processes it is necessary that the voltage remains within an acceptable range. Among the phenomena of interest to electric power quality, which must be eliminated or mitigated, we can mention: harmonics, voltage fluctuation, undervoltage, overvoltage and voltage sags (dips). Due to losses (financial and/or technical) associated with the phenomenon, the interest of this study consists of the voltage sags. In this context, we present a proposal for analysis of voltage sags in an environment with distributed generation (photovoltaic, wind, thermal and biomass-fired power plants) through simulations of short circuits. The results obtained through the proposed methodology shows that the inclusion of DG can bring a change in the number of voltage sags and improve voltage levels in bars, especially in places where they were inserted and in its vicinity. Also, there is a reduction in the number of severe voltage sags which cause more harm and concern to end-users and utilities.

This master’s thesis work deal with diagnosis parameters immunity curves uniphase appliance on short - term voltage dips a interuption. Immunity curve is dependence smallest possible sizes RMS voltage for performance given to criteria function on time continuation voltage event. Curves of resistance is different for each electric appliance, and depending on the size and over-voltage network, the burden on resources and voltage during the event.. The goal of this work is to devise a methodology for measuring the implementation of parametric measurement limit curves of resistance for selected types of appliances.

La tesis doctoral presenta un nuevo método de detección y análisis de eventos en la tensión de suministro de energía eléctrica que utiliza simultáneamente el análisis wavelet y un filtro de Kalman extendido actuando en paralelo sobre las muestras de la tensión. El análisis wavelet proporciona la mejor precisión en la determinación de las características temporales del evento y el filtro de Kalman extendido permite, por un lado confirmar la existencia del evento, descartando aquellas detecciones erróneas que puede producir el análisis wavelet debido a su muy alta sensibilidad, así como determinar con la mayor exactitud la magnitud y fase de la tensión durante el evento.El método desarrollado se ha implementado un tiempo real sobre un sistema DSP, de forma que se adquieren las muestras de la tensión y se analizan sus valores dentro del intervalo de muestreo, para poder detectar y analizar eventos en el menor tiempo posible y poder desarrollar estrategias de protección de los distintos equipos conectados a la red de distribución / The thesis presents a new method for detection and analysis of voltage events in power systems using wavelet analysis and an extended Kalman filter acting in parallel on the voltage samples. The wavelet analysis provides the best estimation of the time-related parameters of the voltage event and the extended Kalman filter enables, on the one hand the confirmation of the beginning and the end of the voltage event, avoiding the erroneous detections that can be produced due to the very high sensitivity of the wavelet analysis, and on the other hand, the estimation of the magnitude and phase angle of voltage supply during the event. The method proposed has been implemented in a DSP-based system, where the voltage samples are analyzed within the sampling period for real-time detection of voltage events.

This diploma thesis deals with evaluation of voltage events regarding to immunity of electric appliances. This thesis is divided into three logical sections. In the first part are shown the voltage events, their definitions, causes and spreading in the mains. The second part deals with measurements and existing possibilities of evaluation of voltage events. The third part deals with suggestion of new evaluation of voltage events regarding to immunity of electric appliances and verification in practice.

This thesis describes an investigation into the influences of arcing and conductor deflection due to magnetic forces on the accuracy of fault locator algorithms in electrical distribution networks. The work also explores the possibilities of using the properties of an arc to identify two specific types of faults that may occur on an overhead distribution line. A new technique using the convolution operator is introduced for deriving differential equation algorithms. The first algorithm was derived by estimating the voltage as an array of impulse functions while the second algorithm was derived using a piecewise linear voltage signal. These algorithms were tested on a simulated single-phase circuit using a PI-model line. It was shown that the second algorithm gave identical results as the existing dynamic integration operator type algorithm. The first algorithm used a transformation to a three-phase circuit that did not require any matrix calculations as an equivalent sequence component circuit is utilised for a single-phase to ground fault. A simulated arc was used to test the influence of the non-linearity of an arc on the accuracy of this algorithm. The simulations showed that the variation in the resistance due to arcing causes large oscillations of the algorithm output and a 40th order mean filter was used to increase the accuracy and stability of the algorithm. The same tests were performed on a previously developed fault locator algorithm that includes a square-wave power frequency proximation of the fault arc. This algorithm gave more accurate and stable results even with large arc length variations. During phase-to-phase fault conditions, two opposing magnetic fields force the conductors outwards away from each other and this movement causes a change in the total inductance of the line. A three dimensional finite element line model based on standard wave equations but incorporating magnetic forces was used to evaluate this phenomenon. The results show that appreciable errors in the distance estimations can be expected especially on poorly tensioned di stribution lines.New techniques were also explored that are based on identification of the fault arc. Two methods were successfully tested on simulated networks to identify a breakingconductor. The methods are based on the rate of increase in arc length during the breaking of the conductor. The first method uses arc voltage increase as the basis of the detection while the second method make use of the increase in the non-linearity of the network resistance to identify a breaking conductor. An unsuccessful attempt was made to identifying conductor clashing caused by high winds: it was found that too many parameters influence the separation speed of the two conductors. No unique characteristic could be found to identify the conductor clashing using the speed of conductor separation. The existing algorithm was also used to estimate the voltage in a distribution network during a fault for power quality monitoring purposes.