Dissertationen zum Thema „Transformer inrush current“

The present PhD thesis deals with transformer inrush current in offshore grids including offshore wind farms and High Voltage Direct Current (HVDC) transmission systems. The inrush phenomenon during transformers energization or recovery after the fault clearance is one of important concerns in offshore systems which can threaten the security and reliability of the HVDC grid operation as well as the wind farms function. Hence, the behaviour of wind turbines,Voltage Source Converters (VSC) and transformer under the normal operation and the inrush transient mode is analyzed. For inrush current reduction in the procedure of the offshore wind farms start-up and integration into the onshore AC grid, a technique based on Voltage Ramping Strategy (VRS) is proposed and its performance is compared with the operation of system without consideration of this approach. The new methodology which is simple, cost-effective ensures minimization of transformer inrush current in the offshore systems and the enhancement of power quality and the reliability of grid under the transformer energizing condition. The mentioned method can develop much lower inrush currents according to the slower voltage ramp slopes. Concerning the recovery inrush current, the operation of the offshore grid especially transformers is analyzed under the fault and the system restoration modes.The recovery inrush transient of transformers can cause tripping the HVDC and wind farms converters as well as disturbing the HVDC power transmission. A voltage control design based on VRS is proposed in HVDC converter to recover ali the transformers in offshore grid with lower inrush currents.The control system proposed can assure the correct performance of the converters in HVDC system and in wind farm and also the robust stability of the offshore grid.
Esta tesis doctoral estudia las corrientes de energización de transformadores de parques eólicos marinos con aerogeneradores con convertidores en fuente de tensión (VSC) de plena potencia conectados a través de una conexión de Alta Tensión en Corriente Continua (HVDC). Las corrientes de energización pueden disminuir la fiabilidad de la transmisión eléctrica debido a disparos intempestivos de las protecciones durante la puesta en marcha o recuperación de una falta. Para la mitigación de las corrientes de energización durante la puesta en marcha del parque esta tesis propone una nueva estrategia basada en incrementar la tensión aplicada por el convertidor del parque eólico en forma de rampa (VRS). Este método persigue energizar el parque eólico con el menor coste y máxima fiabilidad. La tesis analiza diferentes escenarios y diferentes rampas. Otro momento en que las corrientes de energización pueden dar lugar a un disparo intempestivo de las protecciones es durante la recuperación de una falta en la red de alterna del parque eólico marino. Esta tesis extiende la estrategia VRS, utilizada durante la puesta en marcha del convertidor del parque, para los escenarios de recuperación de una falta.

The UK Government has set an ambitious target to achieve 15% of final energy consumption from renewable sources by 2020. High Voltage Direct Current (HVDC) technology is an attractive solution for integrating offshore wind power farms farther from the coast. In the near future, more windfarms are likely to be connected to the UK grid using HVDC links. With the onset of this fairly new technology, new challenges are inevitable. This research is undertaken to help assist with these challenges by looking at possibilities of problems with respect to faster AC/DC interaction modes, especially, on the impact of inrush currents which occur during fault-recovery transients. In addition to that, possible mitigation strategies are also investigated. Initially, the relative merits of different transformer models are analysed with respect to inrush current transient studies. The most appropriate transformer model is selected and further validated using field measurement data. A detailed electro-magnetic-transient (EMT) model of a grid-connected MMC-HVDC system is prepared in PSCAD/EMTDC to capture the key dynamics of fault-recovery transformer inrush currents. It is shown that the transformer in an MMC system can evoke inrush currents during fault recovery, and cause transient interactions with the converter and the rest of the system, which should not be neglected. It is shown for the first time through a detailed dynamic analysis that if the current sensors of the inner-current control loops are placed at the converter-side of the transformer instead of the grid-side, the inrush currents will mainly flow from the grid and decay faster. This is suggested as a basic remedial action to protect the converter from inrush currents. Afterwards, analytical calculations of peak flux-linkage magnitude in each phase, following a voltage-sag recovery transient, are derived and verified. The effects of zero-sequence currents and fault resistance on the peak flux linkage magnitude are systematically explained. A zero-sequence-current suppression controller is also proposed. A detailed study is carried out to assess the key factors that affect the maximum peak flux-linkage and magnetisation-current magnitudes, especially with regard to fault specific factors such as fault inception angle, duration and fault-current attenuation. Subsequently, the relative merits of a prior-art inrush current mitigation strategy and its implementation challenges in a grid-connected MMC converter are analysed. It is shown that the feedforward based auxiliary flux-offset compensation scheme, as incorporated in the particular strategy, need to be modified with a feedback control technique, to alleviate the major drawbacks identified. Following that, eight different feedback based control schemes are devised, and a detailed dynamic and transient analysis is carried out to find the best control scheme. The relative merits of the identified control scheme and its implementation challenges in a MMC converter are also analysed. Finally, a detailed EMT model of an islanded MMC-HVDC system is implemented in PSCAD/EMTDC and the impacts of fault-recovery inrush currents are analysed. For that, initially, a MMC control scheme is devised in the synchronous reference frame and its controllers are systematically tuned. To obtain an improved performance, an equivalent control scheme is derived in the stationary reference frame with Proportional-Resonant controllers, and incorporated in the EMT model. Following that, two novel inrush current mitigation strategies are proposed, with the support of analytical equations, and verified.

Este trabalho apresenta um procedimento completo de simulação da proteção digital diferencial aplicada a transformadores de potência, visando o emprego deste à avaliação do comportamento de relés comercialmente disponíveis. Foi escolhido o software ATP (Alternative Transients Program) como ferramenta para a simulação de distintas situações sobre um sistema diferencial de proteção aplicado a um transformador de 25 MVA. Dentre as ocorrências evidenciadas, destacam-se: situações de faltas internas, faltas externas, situações de energização e energização com falta interna do transformador, condição de sobreexcitação e de saturação de TC (Transformador de Corrente). Cabe comentar que das simulações a real caracterização sobre o relé em teste, fez-se necessário todo um pré-processamento e análise da informação que será convenientemente abordada e justificada no trabalho apresentado, denotando-se um procedimento comum de teste a ser adotado a esta filosofia de proteção. A metodologia e esquema prático adotado trazem uma contribuição importante para a análise laboratorial de modelagens e simulações aplicadas a relés de proteção presentes no mercado e contribui de maneira substancial para os estudos teóricos de possíveis soluções para limitações eventualmente encontradas
This dissertation presents a complete procedure of simulation of digital differential protection applied to power transformers, focusing on its use to evaluate of the behavior of commercially available relays. Software ATP (Alternative Transients Program) was chosen as a tool for the simulation of distinct situations in a differential protection system applied to a 25 MVA three-phase transformer. Amongst the evidenced occurrences internal and external fault conditions, energization with or without internal fault of a three-phase transformer, overexcitation and CT (Current Transformer) saturation conditions were distinguished. It should be mentioned that from simulations to the characterization the real situations on the relay in test, a pre-processing and analysis of the information were necessary, and will be justified in the present study, denoting a common test procedure to be adopted to this philosophy of protection

Transformadores de potência são dispositivos que requerem atenção especial devido a sua grande importância ao sistema elétrico de potência no qual ele está conectado. Geralmente relés diferenciais são utilizados como proteção primária em transformadores de potência. Nestes relés, a corrente diferencial é comparada com um nível de ajuste e caso ocorra uma falta interna, o transformador deverá ser desconectado do restante do sistema. Entretanto, a simples detecção da presença de uma corrente diferencial não é suficiente para distinguir faltas internas de outras situações que também podem produzir tal corrente. Tais situações surgem durante a energização dos transformadores, devido a saturação dos transformadores de corrente, entre outras, as quais podem resultar em uma incorreta atuação da proteção. Uma rápida e correta discriminação entre faltas internas e outras situações é um dos desafios da moderna proteção de transformadores de potência. A respeito da identificação de faltas internas ou situações de energização, além da mencionada lógica diferencial é acrescentado uma subrotina baseada na restrição de harmônicas. Neste método, a corrente de energização é reconhecida através da presença de uma segunda harmônica obtida por filtros de Fourier. No entanto, o método de filtragem pode algumas vezes retardar a operação da proteção. Além disto, uma componente de segunda harmônica pode também estar presente durante uma falta interna. Este trabalho propõe a utilização da transformada Wavelet - uma poderosa ferramenta matemática - empregada como um meio rápido e eficiente de analisar as formas de onda de transformadores de potência e como uma alternativa a tradicional transformada de Fourier. Os sinais das correntes diferenciais são processados pelas transformadas discretas Wavelet, visando obter uma discriminação entre ambas situações (energização e falta). Um nível de limiar é utilizado após a decomposição Wavelet do sinal para discriminar entre as situações descritas. A janela de dados utilizada para este propósito pode ser variada. Para testar o algoritmo proposto, as simulações de energização e falta foram implementadas, utilizando o programa ATP (\"Alternative Transient Program\"). Em situações onde a janela de dados é reduzida para 1/4 de ciclo o critério de discriminação pode ser otimizado utilizando a transformada discreta de Wavelet auxiliada com técnicas de reconhecimento de padrões. Este trabalho apresenta a utilização de redes neurais artificiais para tal finalidade como exemplo. Resultados encorajadores são apresentados sobre a capacidade de discriminação para as situações descritas assim como a rapidez de resposta quando comparados aos métodos tradicionais.
Power transformers are devices that require special maintenance and care due to their importance to the electrical system to which they are connected. Generally, differential relays are used for the primary protection of large transformers. In such relays, differential currents are compared to a threshold and in the case of an internal fault, the transformer should be disconnected from the rest of the system. However, a simple detection of a differential current is not sufficient to distinguish internal faults from other situations that also produce such a current. Some of these situations appear during transformer energization (inrush currents), CT (current transformer) saturation, among others, which can result in an incorrect trip. A correct and fast distinction of internal faults from the other situations mentioned is one of the challenges for modern protection of power transformers. Concerning the identification of internal faults as opposed to inrush currents, the approach tarditionally used is the aforementioned differential logic together with harmonic restraint. In this method, transformer inrush current due to energization is recognized on the basis of second harmonic components obtained by Fourier filters. However, the filtering method can sometimes delay the protection process. In addition to this, a second harmonic component can also be present during internal faults. This work proposes Wavelet transform - a powerful mathematical tool - employed as a fast and effective means of analyzing waveforms from power transformers, as an alternative to the traditional Fourier transform. The differential signals are processed by discrete Wavelet transform to obtain the discrimination between both situations (inrush and fault). A threshold level is utilized after the Wavelet decomposition to discriminate the situations describeb. The time window used for such purpose can be varied. In order to test proposed algorithm, simulations of fault and inrush currents in a power transformer were implemented using ATP ( \"Alternative Transient Program\") software. When the time window is reduced to only 1/4 of the cycle the discrimination criteria should be optimized using a pattern recognition technique to aid the Discrete Wavelet transform. This study shows as a sample for this purpose the use of artificial neural networks. Very encouraging results are presented concerning the capacity of discrimination of the described situations as well as the speed of response when compared to the traditional method.

Hydropower is the most important power balancing resource in the Swedish electrical power system, regulating the power supply to match the load. Consequently, several hydropower plants have periods of stand-by operation where the power production is absent but where several devices within a plant are still active. Such a device is the step-up power transformer, which during stand-by operation still generates no-load energy losses. These losses can accumulate to a considerable amount of energy and costs during the long technical lifetime of the apparatus. One option to minimize these no-load energy losses is by turning the transformer off when its generating unit is in stand-by operation. However, when this transformer operational change has been explained to experts in the field, the most common response has been that a more frequent reenergizing of a transformer leads to higher risks for errors or transformer breakdowns. This study aimed to analytically investigate three effects from this operational change. First, the potential of fatigue failure for the windings due to the increased sequences of inrush current. Secondly, the thermal cycling as a consequence of change in present losses. Lastly, the energy and economic saving potentials for hydropower plants where this operational adjustment is applied. The study used both established as well as analytical tools explicitly created for this study. These were then applied on currently active transformers in different plant categories in Fortum’s hydropower fleet.  The study primarily showed three things. Firstly, risk of fatigue failure due to the increased presence of inrush currents did not affect the transformer’s technical lifetime. Secondly, the thermal cycling changes were slightly larger with absent no-load losses during stand-by operation. The average temperature for the transformer decreased, which in general is seen as a positive indicator for a longer insulation lifetime and thus the transformer’s technical lifetime. Finally, the created frameworks showed the potential of saving energy and money for all plant categories, where the potential grew with the installed production capacity and the stand-by operation timeshare. Despite the simplifications made to describe the complex reality of a transformer operating in a hydropower plant, this thesis contributes to lay a foundation for future investigation of an easy adjustment to avoid unnecessary energy losses and costs for transformers in hydropower plants.

In this thesis is described the function and design of the transformer designed on ferromagnetic core, composed of transformer sheets. It is explained a transient inrush current of the transformer. In this work is inserted voltage and current waveforms, designed printed circuit board, serving to reduce the inrush current.

This thesis investigates the impact of resonant overvoltages and their origin. Series and parallel resonances are present in any electrical grid. The frequency of which this resonance occurs is called resonance frequency. For parallel resonance, which is mainly being studied in this thesis, a high impedance peak can be found at the resonance frequency. This impedance peak in conjunction with a harmonic rich current cause a kind of temporary overvoltages called resonant overvoltages. The harmonic content of the current is high following a fault clearing in the grid, due to transformer saturation. The resonance frequency is heavily dependent on the amount of reactance present in the grid, which entail that a change in reactance causes a change in the resonance frequency. The electromagnetic transient tool PSCAD has been used to investigate resonant overvoltages following transformer energization caused by faults and switching in Stockholm. Secondly, a model was created of a grid connecting off-shore wind power to the mainland via long AC submarine transmission cables. These cables, having a high capacitance, lower the resonance frequency. Faults in this model were simulated to investigate the phenomenon of resonant overvoltages in such a grid. This was especially interesting due to Swedens planned expansion of wind power in the Baltic sea. While resonant overvoltages were found in Stockholm they were not deemed significant due to their low magnitude and longevity. However, severe resonant overvoltages were found in the off-shore wind farm model. The worst resonant overvoltages had a maximum amplitude of the 2nd order harmonic voltage of 130 kV which, while eventually damped, were significant for up to 50 periods. Lastly, the phenomenon of an increased resonance frequency during the saturation of a transformer was studied. The most severe resonant overvoltages occured in a model where the frequency scans showed a resonance frequency of 98 Hz. Indicating, caution needs to be had during EMT-studies of resonant overvoltages while choosing what resonance frequency to study.

Lors de la réalimentation des auxiliaires d'une tranche nucléaire ou hydraulique, l'étape la plus à risque est la remise sous tension brusque du transformateur à cause des surtensions et courants d'appels générés. Ces phénomènes transitoires engendrent des effets très indésirables autant pour le réseau comme pour le transformateur (efforts électrodynamiques sous les bobinages, vibration du circuit magnétique, bruit et vieillissement prématuré du transformateur.) Le but de ces travaux de thèse est de proposer de nouvelles méthodologies permettant d'évaluer les paramètres mal connus (les valeurs des flux rémanents présents dans le circuit magnétique du transformateur avant sa mise sous tension). Face aux problèmes actuelles pour l'estimer (méthode non directe, dérive, imprécision de la mesure de la tension, etc.), deux nouvelles méthodes basées sur la magnétisation préalable du circuit magnétique (méthode de prefluxing) et sur la mesure des flux de fuites du circuit magnétique (méthode de mesure directe de flux par mesure de l’induction magnétique) sont proposées
During the re-energization of the auxiliaries of a nuclear or hydraulic power plant, the most dangerous step is the re-energization of the power transformer, because of the temporary overvoltage and inrush currents. These transients phenomenon causes undesirable effects for both network and for the power transformer (electrodynamic forces over the windings, the magnetic circuit’s vibration, noise and the premature aging of the transformer). The goal of these thesis is to suggest new methodologies allowing us to evaluate unknown parameters (the residual flux’s values in the magnetic circuit before transformer’s energization). According to the latest problems in order to evaluate it (no direct method, derivation, voltage measurement error, etc) two new methods based on the previous magnetization of the magnetic circuit (prefluxing method) and on the leakage flux measurement of the magnetic circuit (direct measurement of the flux by measuring the magnetic induction method) are proposed

Le transformateur de puissance est un équipement essentiel d'un réseau électrique et le plus coûteux dans les postes. Pour augmenter son degré de disponibilité et de fiabilité, il est nécessaire d'appliquer la manœuvre contrôlée afin de diminuer la saturation du noyau lors de l'enclenchement, et donc limiter les courants d'appel. Ces derniers sont asymétriques, d'amplitude élevée, et riches en harmoniques. Ils peuvent causer des effets indésirables comme le disfonctionnement des dispositifs de protections, l'endommagement mécanique des enroulements du transformateur et réduire en général la durée de vie et la qualité des systèmes. Une technique efficace pour réduire ces courants d'appel est de mettre sous tension le transformateur quand le flux dynamique généré par la source est égal à son flux rémanent. Un modèle simplifié du transformateur de puissance est adopté pour l'analyse des phénomènes physiques liés à l'application des manœuvres. Pour évaluer le degré de faisabilité de cette technique, des simulations sont effectuées en utilisant le simulateur de réseau EMTP. Les contraintes requises pour chacun des composants du système de manœuvre contrôlée comme les segments de ligne, les disjoncteurs sont étudiées en détail pour déterminer l'algorithme de calcul de l'instant optimal de manœuvres. Ensuite des tests de validation statistiques sont effectués afin d'évaluer les performances des différentes approches employées. Enfin une étude consacrée à la reconstitution du flux rémanent via un transformateur capacitif de tension (TCT) est menée pour appliquer l'algorithme de manœuvre contrôlée dans les postes en utilisant les équipements de mesure déjà existants.

This dissertation presents the development of an algorithm for classifying electrical transients in power transformers for protection. Initially the main transient involving power transformers were analyzed, with a special focus on the magnetizing current that occur during energizing equipment, known as inrush currents. Among the studied transient, current inrush are those that present greater difficulty in identification and discrimination by the differential protection, due to its high peak magnitude. In a second moment, was developed a test system implemented in ATP / EMTP software for the simulation of different operating situations of the power transformer, current data being obtained from TCs for analysis. After known the problem and implement a test for acquisition system, we developed an algorithm based on the last samples of the detail coefficients, called Details Signals, from the decomposition of the data of differential phase current using the Discrete Wavelet Transform. The methodology has the objective improve the system for protection of the transformer, becoming one efficient alternative for the identification of transients.
Esta dissertação apresenta o desenvolvimento de um algoritmo para classificação de transitórios elétricos em transformadores de potência, para fins de proteção. Inicialmente foram analisados os principais transitórios associados aos transformadores de potência, tendo um foco especial na corrente de magnetização que surge durante a energização do equipamento, conhecida como corrente de inrush. Dentre os transitórios estudados, as correntes de inrush são as que apresentam maior dificuldade de identificação e discriminação por parte da proteção diferencial, devido a sua alta magnitude de pico. Em um segundo momento, foi desenvolvido um sistema teste implementado no software ATP para a simulação das diversas situações de operação do transformador de potência, sendo obtidos dados de correntes a partir dos TCs para análise. Após conhecer o problema e implementar um sistema teste para a obtenção dos dados, desenvolveu-se um algoritmo baseado nas últimas amostras dos coeficientes de detalhes, chamada de Sinais de Detalhes, provenientes da decomposição dos dados de correntes diferenciais das fases por meio da Transformada Wavelet Discreta. A metodologia desenvolvida tem como objetivo melhorar o sistema de proteção do transformador, tornando-se uma alternativa eficiente para a identificação de transitórios.

博士
國立成功大學
電機工程學系碩博士班
93
This dissertation proposes a novel approach for transformer design that reduces the inrush current by employing an asymmetrical winding configuration. Different from the symmetric winding structure of traditional transformer designs, the proposed method can provide both a high inrush equivalent inductance for reducing inrush current and a suitable leakage inductance for voltage regulation and short-circuit current in the transformer. In order to estimate a satisfactory distributive ratio for the asymmetrical winding configuration before manufacture, in this research the inrush equivalent inductance and the leakage inductance are derived from the structural parameters of the transformer. Furthermore, for proving the influences of the inrush equivalent inductance on inrush current, a magnetizing inrush model for the transient period of inrush current is presented. In the magnetizing inrush model, the relationship between the magnetic flux density and magnetic field intensity differs from the ordinary B-H curve, the magnetic characteristics of core are presented by H-B planes and the B-H curve can be represented as a simple tangent function. Using the magnetizing inrush model, the inrush current can be estimated before the transformer is manufactured. Proofs of the influences of the inrush equivalent inductance are also provided. 　　Through the theoretical analyses, the desirable winding configuration is presented that allows the inrush current to be reduced with appropriate voltage regulation and short-circuit current. Moreover, the inferential results are successfully obtained substantiation from the experiments.

碩士
國立成功大學
電機工程學系碩博士班
97
This thesis investigates the application of intelligent electronic device to suppress the inrush current of transformer. This study is motivated because the magnitude of inrush current is often several times higher than that of rating current of transformers, by which the performance of protection relays is often affected. Thanks to high flexibility of programming function of intelligent electronic device, it is applied to reduce the impact of transformer inrush current. Meanwhile, the protection coordination of radial distribution system would become more reliable. To ensure the practical value of this proposed strategy, the method has been validated with transformer tests by measuring the resulted current waveforms. It is anticipated that these results can decrease the probability of equipment damage, thereby ensuring a high-quality power-supplying system.

碩士
國立臺北科技大學
電機工程系碩士班
92
Because of magnetic saturation of transformer cores and residual flux, the magnetizing inrush current may reach several times the rated value , when a transformer is instant energized , thus a transient over current different from normal short circuit fault current would easily cause protective relay abnormal action and unusual trip of breaker. Therefore, in this research we try to use physical structure to lead to lump parameters of saturable transformer models. The models’ parameters are not known by the same way as those known from normal factory test by using open-circuit test (no-load current test and no-load lose test) and short-circuit test (load lose test and impedance voltage test). In addition, parameters in need could be found from the designed data of the transformer before manufacturing. We will use electromagnetic transient programs (ATP-EMTP) to simulate relevant waves which we will compare with the measured to testify that the model is accurate. After that, we will have the comparison of those input characteristic impedance when the winding is instant switched-in by two transformers with different capacity to find the relationship between capacity versus input impedance and magnetizing inrush current. Besides, simulating the correlated inrush current’s changes and harmonic content by different angles of the energizing voltages and with, or without residual flux, and discuss by which situation the most inrush current and harmonic content are given. Thus, we will have the conclusion and the way to improve.

碩士
國立成功大學
電機工程學系碩博士班
92
For the high-tech or traditional industry, the stable power supply is always a very critical requirement, where the transformer is deemed a supply hub for the supplying power. It is also hence commonly recognized that the transformer protection should be prudently designed. However, because of nonlinear characteristics of tansformer coils, it often lead to the scenario of huge amount of inrush current once the power source is switched on, thereby even causing the misoperation of protective relays. In view of such drawbacks, this thesis is, therefore, aimed at the identification of transformer inrush current through the wavelet transform aided with the field programmable gate array. In other words, the time-frequency localization and multi-resolution capabilities of wavelet transform are both employed to distinguish the occurrence of inrush current, where the hardware realization is also accomplished. To validate the effectiveness of this proposed scheme, the approach was also individually tested through the simulation signals and experimental data. The test results confirm the practical values of the proposed method.

碩士
逢甲大學
資訊電機工程碩士在職專班
99
Abstract The power transformer is one of the most important pieces of equipment in a power system. Due to frequent power on or off and the instantaneous of power lines and failure transmission, electromagnetic effects cause radial(horizontal) and axial(vertical)stress , resulting in the deformation and distortion of the coil winding, collision of the winding insulation and damage to the transformer. The objective of this thesis is to measure through the Nicolet transient recorder the transformer data (inrush current, input voltage, flux,etc.) before and after light damage and turn-to-turn short-circuit damage, in order to conduct the Matlab analysis and compare before and after discrepancies. This study uses a system consisting of a single phase, three winding 3kVA 220V/110V-220V oil-immersed transformer, one of a set of 110V coil windings, and an LM-358-OPAmp integrated circuit . A Nicolet transient recorder measures and records the data that is then translated by Matlab software into waveform analyses of input voltage, inrush current, flux, BH curve, etc. Finally, the Power Differential Method is used to calculate the transformer''s power consumption and from the difference between the internal one-turn short-circuit fault current and the magnetizing inrush current, identify the deformation or failure of the winding. This experiment proves the power consumption of the distorted internal coil winding and the failed one-turn short-circuit transformer is 3-10 times greater then that of a normal magnetizing inrush current, thus providing a clear distinction between the normal and failed transformer.

碩士
國立虎尾科技大學
電機工程研究所
98
In this paper, the differential protection devices for the transformer is one of the basic principles of long maturity, the protection device of the most critical and most difficult problem is how to prevent the magnetizing inrush current caused by differential protection device malfunction, which offered exciting inrush current discrimination measures. How to correctly distinguish the transient magnetizing inrush and fault current can be timely and accurate identification, in order to effectively achieve the purpose of identification. Therefore, this study in no-load transformer input waveform generated by the process of detection, using the shock response spectrum analysis method can effectively identify non-periodic signal transient excitation inrush and fault current. The Matlab software simulation mean calculus SRS, analysis of inrush current signals, extract and address the inrush current characteristics especially for the fundamental wave and the second harmonic of the main features, and diagnostic transformer state. SRS analysis can be found to reliably identify the inrush current and fault current. The digital signal controller is used to design detection circuit, and reach an real-time judge of the effects of inrush current.

碩士
國立虎尾科技大學
電機工程研究所
96
Integration of automatic test of transformer inrush current and shock response spectrum analysis using LabVIEW software is discussed in this thesis. The LabVIEW is a software language with emphasis on computer automation flow chart type. It has strong data acquisition and instrument control ability. It can be applied to analyze and judge data immediately. In this thesis, the LabVIEW is used to measure and analyze inrush current. The experimenttal results are presented by virtual instruments. The purpose of automatic testing and spectrum analysis can be reached. The developed automatic testing system is mainly based on the Programmable System on Chip (PSoC). It is used to design control circuit for function of the automatic testing. Besides, the shock response spectrum analysis method is applied to distinguish transient inrush current from fault current. The developed man-machine interface of the integrating system has good humanistic design. Finally, the integrating system is examined by experimental results with Photon II vibration spectrum analysis instrument. The good accuracy and practicality of the proposed integrating system is uerified from the measured results.

碩士
國立聯合大學
電機工程學系碩士班
96
The power transformer is one of several expensive equipments in power systems . Once the power transformer is malfunctioning, it will cause an unbalanced power supply , which may further lead to the loss of power and utilities need to pay a huge repair expense . Unfortunately , the electric utilities have not yet found effective prevention methods for this kind of problems so far . With the fast development of electric power technology and the continuous efforts made by the power engineers, the possibility of solving the above problems has appeared . The main objective of this study is to investigate an online recognition system for power transformers . The study uses MATLAB software and its related programs as the simulation tool to analyze the power transformer inrush currents in the blink of energizing , which tend to cause the oscillation phenomena within the inside insulating materials, cores and coils , i.e. the inherent capacitance, resistance and inductance. In terms of this phenomenon , various key feature indices can be derived, moreover , by using neural networks the normal inrush currents and possible abnormal symptoms of the power transformer can be identified. The feasibility and effectiveness of the proposed method have been proved by detailed theoretical studies and comprehensive simulations carried out in this study . It is worth to note that with some modifications the proposed method can be further developed into a real-time diagnosis and protection system for the power transformers .

碩士
國立虎尾科技大學
電機工程研究所
98
A credible protection system for a power transformer includes both of the reliability and safety. Reliability means that the schemed protection zone in a protection system will promptly and accurately respond to an intolerable disturbance due to a power failure in the power grid. While safety means that it won’t respond to any power failure beyond its own protection zone which could otherwise results in an unlimited area of blackout. The principle of differential protection device for power transformer has long been developed. This paper aims at the know-how of how to prevent a differential protection device from malfunctioning caused by the magnetized inrush current. Then a counter measure is presented on how to discriminate and judge the magnetized inrush current. Firstly , we use the technique of Shock Response Spectrum (SRS) to analyze and identify the magnetized inrush current. In addition to compute SRS with Matlab S/W , we then can pinpoint the characteristics of magnetized inrush current. Further , with which , we found out the analysis of SRS is credible for discriminating the magnetized inrush current. Moreover , it is practicable to be burned in a programmable chip (ds PIC ) or other peripheral equipments which leads to a real time and effective way of discrimination. Finally , in order to promote the reliability of power supply , we incorporate the technique with the s/w Matlab to simulate the varieties of fault currents and its influence of power load dispatching. As in whole , by analyzing the index of SAIDI ( System Average Interruption Duration Index ) and SAIFI ( System Average Interruption Frequency Index ) , we see the efficiency and strength of this research which not only contribute to the reliability of power supply but also coincide the demand of protection system.