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Voltage Sag Evaluation Method of a Real Distribution System Based on a Connection Number Model
Applied Mechanics and Materials
Abstract
The evaluation results of power system are greatly influenced by the reliability parameters and uncertainty of system components. The connection number assessment model and an approach have been presented to assess the occurrence frequency due to voltage sags. The proposed method had been applied to a real distribution system. Compared with the interval number method, the simulation results have shown that this method is simple and flexible.
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In this paper, voltage sags produced by balanced and unbalanced short circuits are analyzed by means of a new analytical method. The main feature of this approach is that contrary to the fault positions method, it does not require a preassignation of discrete fault positions along the lines. The developed algorithm has been applied to the 24-buses IEEE Reliability Test System (RTS) and to a real transmission system to illustrate its application. Results are analyzed and compared with the fault positions method. The mathematical formulation of the proposed approach is straightforward and different fault distributions along the lines can be effortlessly considered. The proposed method is adequate for the analysis of any size networks.
This paper discusses the sensitivity of personal computers (PCs) to voltage sags and short interruptions on the basis of the extensive test results. Existing standards and previously published works are reviewed, and a description of a used testing procedure is presented. The following tests were performed: sensitivity to rectangular voltage sags with ideal and nonideal supply characteristics, and sensitivity to voltage sags caused by the starting of large motors. The results obtained emphasize the importance of clear definition of the malfunction criteria for this equipment.
The sensitivity of sensitive equipment to voltage sag is usually expressed by the failure rate of equipment caused by voltage sag. The failure rate depends on the characteristics of voltage sag at power supply site and the equipment voltage tolerance. These characteristics are uncertain resulting in the difficulty in assessment and prediction. The uncertainties of voltage sags and voltage tolerance of sensitive equipment were synthetically considered to assess the failure rate of sensitive equipment due to voltage sag. The events of equipment failure due to voltage sags were defined as fuzzy-random events. The concept of fuzzy-random variable was introduced to describe the variety of sensitive equipment failure event caused by voltage sag. The fuzzy-random based assessment principle and approaches were proposed. The method of λ-cut sets for the fuzzy-random variable was used to convert the problem of fuzzy-random probability into classical probability problem. This method had effectively ensured the feasibility of the assessing method. The proposed method was used to assess the sensitivity of personal computers to voltage sags. The simulation results were compared with the results of Monte Carlo simulation also. It has been proved that the proposed method is proper and feasible and the evaluation results are consistent with the practical experiences.
The concept of power quality comprehensive evaluation (PQCE) for regional grid has been proposed. The regional grid power quality has been analyzed in hierarchy. First, the PQCE of each substation bus has been done by genetic projection pursuit method (GPPM). This process could pick-up the characteristic of power quality index and overcome the influence of subjective factors in traditional evaluation methods. Then the weights of the GPPM comprehensive evaluation outcomes were proposed by the eigenvalue weighted method. The PQCE results of the regional grid and its each voltage level and each substation can be acquired by the weight. The power quality of regional grid can be reviewed from the local to overall by means of this evaluation results.
This paper presents a summary of the work performed by the authors on voltage sag analysis using a time-domain tool. The document describes a procedure for stochastic prediction of voltage sags based on the Monte Carlo method. A medium size distribution network is used to analyze the advantages of this approach, the convergence of the Monte Carlo method, the influence of protective devices and the importance of voltage sag indices. The limitations of the present version and the future work are also discussed.
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