4 research outputs found

    An Initial Investigation for Locating Self-Clearing Faults in Distribution Systems

    No full text

    Operation of soft open point in a distribution network under faulted network conditions

    Get PDF
    A Soft Open Point (SOP) is a power electronic device, usually implemented using back-to-back voltage source converters (VSCs) installed at normally-open points (NOP) of a distribution network. SOPs are typically utilised to enhance distribution network operation, under normal network conditions. Their applications include power loss reduction, feeder load balancing, network reinforcement, voltage profile improvement and distributed generation (DG) connection support. This thesis investigates the operating principle and applications of a back-to-back VSC based SOP under faulted network conditions. The dynamics of a network with SOP were observed during normal and faulted network conditions. The conventional fault analysis technique using symmetrical components was extended to include SOP, such that it can be applied on distribution networks with SOP. Equivalent sequence networks were developed for different type of faults, including phase-to-ground faults, phase-to-phase faults and three-phase faults. The correlation between the symmetrical components (of voltages and currents) at the SOP grid connection point and the SOP set points were studied. A simple but effective method of fault detection during grid-connected operation was formulated using the sequence voltages at the grid connection point of the SOP. The impact of the SOP dynamics on a conventional distributed feeder automation (D-FA) scheme was investigated. It was found that the current contributed from the SOP during a fault could potentially disturb the protection coordination of the network. Consequently, the sequence of events in a feeder automation scheme is disrupted if the SOP is kept operational beyond the fault ride-through period. A new operating mode was defined to operate the SOP during network faults such that it can be co-ordinated with network protection. Based on the local measurements at SOP grid connection point, methods to determine the presence of a fault, fault type and location of a fault were investigated. A D-FA scheme was proposed, in which the fault diagnostic capability of an SOP was utilised to coordinate the feeder automation sequence. Substantial improvements were achieved in both the restoration time and life of existing switchgear by using SOPs for feeder automation. The fault diagnostic capability of an SOP was validated using a power hardware-in-the-loop (PHIL) experimental setup. A VSC prototype with a constant DC voltage source was used to emulate an SOP. The prototype was integrated with a distribution network modelled in the real-time digital simulator (RTDS), through a power interface. Individual protection features of the SOP including fault detection, fault type identification and estimation of fault location were validated using this experimental setup. The results obtained using the real-time PHIL experiment were consistent with the results obtained using software simulations

    Localização de faltas incipientes em sistemas de distribuição de energia elétrica com cabos subterrâneos

    Get PDF
    Nos sistemas de distribuição de alta e média tensão tem-se aumentado a utilização de linhas de distribuição de energia subterrâneas ou cabos subterrâneos. A ocorrência de faltas nas linhas afeta negativamente a qualidade da energia e o correto funcionamento da rede. O processo que leva a uma falta nos cabos é gradual e está caracterizado por uma série de subciclos de faltas incipientes associadas a uma tensão de arco. Estas, muitas vezes, passam despercebidas e, eventualmente, resultam em uma falta permanente. Os métodos clássicos de localização de faltas como as metodologias baseadas no cálculo da impedância aparente, as baseadas na inteligência artificial e as baseadas nas ondas viajantes são, habitualmente, aplicadas ao sistema depois de uma falta permanente acontecer e precisam de um ou mais ciclos do sinal para entregar uma resposta razoável. No entanto, as faltas nos cabos são um processo gradual, de curta duração (entre ¼ e ½ ciclo do sinal) e seria desejável localizar a falta incipiente antes de tornar-se permanente. Nesse contexto, esta pesquisa aborda o problema de localização de faltas incipientes. Assim, nesta tese propõe-se uma nova técnica de localização de faltas incipientes usando medições em um terminal, no domínio do tempo e que utiliza componentes de fase. Desta forma, são desenvolvidas duas novas formulações do modelo elétrico do sistema de distribuição com cabos subterrâneos durante uma falta incipiente. A abordagem proposta considera simultaneamente na sua formulação características da falta incipiente e dos sistemas de distribuição de energia, como a tensão de arco, o modelo Π nominal de parâmetros concentrados do cabo subterrâneo, o desequilíbrio do sistema e a condição da carga. A estimativa da distância da falta, junto com os parâmetros da falta incipiente, é obtida a partir da solução de um sistema sobredeterminado de equações lineares pela aplicação do método de mínimos quadrados ponderados não negativos. As formulações propostas permitem estimar a distância da falta em termos da reatância da linha até a falta. Além disso, é proposto um processo de compensação de corrente para estimar a corrente de falta; é aplicado um pré-processamento dos dados de entrada para suavizar o efeito do ruído que pode conter o sinal e, é aplicado um pós-processamento dos resultados para refinar e entregar a melhor estimativa obtida durante o processo de localização da falta. O desempenho da técnica proposta é avaliado mediante estudos de casos simulados em um circuito real de distribuição no Alternative Transients Program (ATP/EMTP) considerando análises de sensibilidade e comparativa. Também, o modelo da falta incipiente foi programado utilizando a ferramenta de MODELS do ATP/EMTP. Os resultados obtidos, considerando faltas incipientes simuladas que avaliam a influência da variação da magnitude de tensão de arco, do ruído aleatório inserido na tensão de arco, da distância da falta, da taxa de amostragem, do carregamento do sistema, do modelo de tensão de arco e de incertezas nas medições, indicam claramente que a abordagem proposta possui validade como técnica de localização de faltas incipientes, apresentando erros médios globais de 1,60% e 0,93%, respectivamente para cada formulação proposta.The use of underground power distribution lines or underground cables in the high and medium voltage distribution systems has increased dramatically in recent years. The fault occurrence in the distribution lines negatively affects the power quality and the correct network operation. The process which leads to a fault in underground cables is gradual and is characterized by a series of sub-cycles of incipient faults associated with an arc voltage. These often are unnoticed and, eventually, results in a permanent fault. Classical fault localization methods such as the based-impedance, the based on artificial intelligent and the based on traveling waves are, usually, applied to the system after a permanent fault occurrence and need one or more signal cycles for providing a reasonable response. However, the faults in cables are a gradual process, with short duration (between ¼ to ½ of signal cycle) and would be desirable to locate the fault before this becomes a permanent fault. In this context, this research approaches the incipient faults location problem. Thus, in this thesis is proposed a new incipient fault location technique using single-end terminal measurement, in time-domain and employing phase components. In this way, two new formulations of the electrical model of the distribution system with underground cables during an incipient fault are developed. The proposed approach considers simultaneously in its formulation, incipient fault type and power distribution systems characteristics as arc voltage, unbalanced operation, load conditions and complete line model. The fault distance estimation, together with the incipient fault parameters, it is obtained from the solution of an overdetermined linear system of equations by the application of the non-negative weighted least squares estimator method. The proposed formulations allow estimating the fault distance in terms of the line reactance up to the fault. In addition, a load current compensation strategy is proposed to reduce its effect in the fault current estimation; an input data pre-processing is applied to smooth out the noise effect and a post-processing of the results is performed for estimation refinement and to provide the best estimate obtained during the fault location process. The proposed technique performance is evaluated through simulated cases studies in a real-life distribution network with underground cable data in the Alternative Transients Program (ATP/EMTP) considering sensitivity and comparative analyzes. Also, the fault model was programmed using the MODELS tool of ATP/EMTP. The obtained results, considering simulated incipient faults, which evaluate the influence of variations in the arc voltage magnitude, random noise percentage inserted in the arc voltage, fault distance, sampling rate, load dynamics, the arc voltage model and uncertainties in measurements, indicate clearly that the proposed approach is valid as incipient faults location technique, showing overall average errors of 1,60% and 0,93%, respectively for each proposed formulation
    corecore