After a fault occurs in a powersystem, generally some operating information of protective relays and circuit breakers could be obtained. Because protective relays and circuit breakers might improperly operate or fail...
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After a fault occurs in a powersystem, generally some operating information of protective relays and circuit breakers could be obtained. Because protective relays and circuit breakers might improperly operate or fail to operate, and some errors and distortion may exist in data acquisition and communication, as a result uncertainties could be involved in the received information. A fault diagnosis model based on fuzzy set-covering theory and mode identification technique is proposed in this paper. With the fuzzy technology, the above mentioned uncertainties could be dealt with very well. Meanwhile, as the protective relays and circuit breakers may fail to operate in some cases, there are several different operating modes in protective relays and circuit breakers even for a same electrical device failure. Based on the received information, the proposed model could identify the most possible operating mode, and then the information corresponding to a fault hypothesis could be obtained. In the proposed model, the proposed fault diagnosis problem is described as a 0-1 integer programming one, and thus could be solved by the widely employed search technology, i.e., the well-known Tabu search method. The feasibility and efficiency of the proposed model is demonstrated by a sample powersystem.
powersystem restoration decision-making is one of the most important and indispensable issues for ensuring fast power supply restoration to end users. In recent years, the power industry around the globe has been und...
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powersystem restoration decision-making is one of the most important and indispensable issues for ensuring fast power supply restoration to end users. In recent years, the power industry around the globe has been undertaking an in-depth restructuring, and this has led to some new challenges to the problem of powersystem restoration. In this paper, several important issues related to powersystem restoration in the traditional power industry and in the electricity market environment are analyzed and compared, and then the impacts of the restructuring efforts on the powersystem restoration are identified and clarified from several aspects including black-start, restoration tests, dispatching and distribution system service restoration. Up to now, in most of the practically operating electricity markets around the globe powersystem restoration ancillary service is still based on cost compensation rather than market mechanism.
Voltage sag, one of the modern power quality problems, may cause tremendous economic loss, which needs scientific method to evaluate. This paper proposes an approach using quality loss function and signal-to-noise rat...
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Voltage sag, one of the modern power quality problems, may cause tremendous economic loss, which needs scientific method to evaluate. This paper proposes an approach using quality loss function and signal-to-noise ratio (SNR) in quality engineering theory to make economic assessment to voltage sag. The inverted normal probability loss function is used to describe losses of single-type sags, where SNR method is applied to integrate different types together. The index of sag-caused loss is proposed, which is an important parameter for PQ evaluation. A five-node 35 kV distribution system is used to verify the proposed approach. The result shows that the proposed method could effectively assess financial losses caused by sags and be a reasonable instruction for PQ evaluation, improvement and pricing.
Synchronized phasor measurement technology has been gaining increasingly interests in China due to its wide area time synchronization capability and fast transmission speed. Over 10 years of implementation of wide are...
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Synchronized phasor measurement technology has been gaining increasingly interests in China due to its wide area time synchronization capability and fast transmission speed. Over 10 years of implementation of wide area measurement system (WAMS) in Chinese power grid have shown its great value in powersystemdynamicmonitoring and potential applications in system modeling and validation, feedback control and system wide protection. This paper reviews the overall implementation of WAMS in China and analyzes the corresponding characteristics of WAMS. Moreover the challenges for bulk powersystemprotection with synchronized phasor measurement technology are presented also.
Load modeling is very important to powersystem operation and control. Measurement-based load modeling has been widely practiced in recent years. Mathematically, measurement-based load modeling problem are closely rel...
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Load modeling is very important to powersystem operation and control. Measurement-based load modeling has been widely practiced in recent years. Mathematically, measurement-based load modeling problem are closely related to the parameter identification area. Consequently, an efficient optimization method is needed to derive the load model parameters based on the feedback of estimation errors between the measurements and model outputs. This paper reports our work on applying genetic algorithms on measurement-based load modeling research. Due to its robustness to the initial guesses on the load model parameters, genetic algorithms are very suitable for load model parameter identification. Two cases including both the real measurement in a power station and the digital simulation are studied in the paper. For comparison purpose, the classical nonlinear least square estimation method is also applied to find the load model parameters. The simulated outputs from the load model confirm the efficiency of genetic algorithms in measurement-based load modeling analysis. Future work will focus on fastening the converging speed of the genetic algorithms, and/or utilizing more efficient evolutionary computation methods.
Load modeling is very important for powersystemdynamic analysis and control. The composite load model widely applied recently in the powersystem operation centre consists of the static load and the equivalent motor...
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Load modeling is very important for powersystemdynamic analysis and control. The composite load model widely applied recently in the powersystem operation centre consists of the static load and the equivalent motor. Current practices in measurement-based load modeling identify all the parameters in this composite load model. However, it is not clear whether all these parameters could be identified from the measurements. This paper investigates the identifiability of the equivalent motor parameters in the composite load model. Trajectory sensitivity approach is applied first to find the motor parameters that have great effects on the measured active as well as reactive load dynamics. The analysis results show that the motor outputs have various sensitivities with respect to the parameters. Since the voltage disturbance, the active load and the reactive load dynamics are applied to identify the motor parameters, those parameters affecting the measurements to a great extent are observable, thus identifiable from the measurements; while those that have little effects on the motor outputs are unobservable from the measurements and consequently unidentifiable. The case studies verify the identifiability of the motor parameters.
This paper presents a model and control strategy for one multi-module-converter based VSC-HVDC system. Each converter operates with a fairly low switching frequency, and thus it is applicable to select high-power low-...
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This paper presents a model and control strategy for one multi-module-converter based VSC-HVDC system. Each converter operates with a fairly low switching frequency, and thus it is applicable to select high-power low-switching-frequency and low-conduction-loss electronic devices such as IGCT or GTO in high-power applications. A mathematical model is developed for the overall multi-module-converter based VSC-HVDC system. A controller is also designed systematically for the HVDC system based on the developed system model. Performance of the overall HVDC system and effectiveness of the designed controller are evaluated based on digital time-domain simulations in the MATLAB software environment.
Recent years, some DG (distributed generation) have been introduced in distribution systems, and the voltage violation problem has been at stake for the distribution system. The impact of DG integration on distributio...
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Recent years, some DG (distributed generation) have been introduced in distribution systems, and the voltage violation problem has been at stake for the distribution system. The impact of DG integration on distribution system is studied in this paper, and the transient stability mechanism of DG is analyzed theoretically. This paper investigates the dynamic analysis of a DVR when applied to correct the voltage distortion in distribution system. Then the model of DG is built by Matlab/Simulink. And it is used to study the impact of DG integration on the distribution system. Then the voltage regulation-dynamic voltage restorer (DVR) is introduced to distribution network with distributed generation. A calculation method for DVR in distribution system with distributed generation is proposed, which is based on a semi-period algorithm to extract fundamental component from fault signal then extract the fundamental positive sequence voltage by the decomposition instantaneous link, and then the quantity of voltage compensation can be solved by direct detection algorithm. Simulation results show that the introduction of DVR (dynamic voltage restorer) to the distribution system with distributed generation is good for voltage regulation and making a good guarantee of the voltage quality of sensitive loads; and the algorithm for DVR is simple and effective.
Currently, the pollution performance of silicone rubber (SIR) insulators is mainly evaluated by the clean fog test method, in which the wetting time of a tested sample is kept within 1 to 2 hours. The objective of thi...
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Currently, the pollution performance of silicone rubber (SIR) insulators is mainly evaluated by the clean fog test method, in which the wetting time of a tested sample is kept within 1 to 2 hours. The objective of this paper is to validate if it is necessary to take the longer wetting time than 2 hours for SIR insulators in the clean fog test. A type of kieselguhr-polluted SIR insulators with the strong surface hydrophobicity was evaluated in a unique environmental test chamber. Each insulator was tested for 24 hours or until a flashover occurred. The test results show that it took 8 hours to 14 hours for some tested insulators to flash over at the scheduled levels of high voltages, due to the gradual decrease in surface hydrophobicity and the consequential increase in wettability with time under the fog conditions. However, the leakage current along the insulator surfaces had no remarkable development before the flashover occurred. The test results prove that it is necessary to take much more wetting time than 2 hours to evaluate the flashover performance of SIR insulators in the clean fog test. Furthermore, another test on the kaolin-polluted SIR insulators with the weak surface hydrophobicity indicated that in order to obtain the lowest pollution flashover voltages of SIR insulators under long-time wetting conditions, the fog parameters should be reasonably chosen to avoid the heavy lose of the salt density on the insulator surfaces with time.
The radiation and propagation of electromagnetic (EM) waves generated from PD caused by the obstruction of main transformer components are studied by FDTD simulation in order to get more information for PD location an...
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The radiation and propagation of electromagnetic (EM) waves generated from PD caused by the obstruction of main transformer components are studied by FDTD simulation in order to get more information for PD location and diagnosis. Current filament, perfect conductive cylinder and perfect conductive spiral coil models are used to simulate the radiation and the influences of iron-core and transformer coil to the propagation of EM waves. The results demonstrate dynamic propagation process of EM waves in time order, and prove the correctness of the shortest optical path principle. But the attenuation and distortion of EM waves-especially the first peak amplitude-caused by the obstruction of large solid conductive obstacle like iron-core are quite intensive that it may cause great difficulties to identify exact arriving time position of incident waves coming along the shortest optical path. While the influences of the coil to the propagation of EM waves are so little that HF EM waves can penetrate it in almost linear path.
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