Papers by Author: Xian Yong Xiao

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Authors: Xu Na Liu, Ying Wang, Xian Yong Xiao
Abstract: In order to accurately describe the equipment’ severity caused by voltage sag, the credibility measure which meets the conditions of non-additive is proposed based on their physical properties of responses. This assessment measure can avoid the deficiencies that classical probability measure needs a large number of samples and the non-duality of fuzzy measure. The membership functions of sensitive equipment voltage tolerance capability that corresponding to the characteristic quantities in the status uncertain area was determined by fuzzy statistical method and polynomial fitting method. Then the joint credibility distribution function was deduced based on uncertainty theory. Hence, the assessment model of severity of equipment failure is constructed. Based on practical samples, the PCs were simulated using the proposed method. Comparing the simulation results with methods using classical probability measure and possibility measure prove that the proposed method is proper and credible and can reflect practical condition more objectively.
Authors: Tian Wen Zheng, Jian Wen Yang, Xian Yong Xiao, Ying Wang
Abstract: The bus will experience different voltage sag when fault occurs at different location. Based on the non-liner profile characteristic of voltage sag measured at the bus, the paper proposes a new fault location method. Firstly, it obtains the analytical expression of each section based on the relationship between voltage sag and fault location. Then calculate the fault distance using chord secant method and identify the faulted section through the minimal deviation of fault distance. The combined two results of fault distance and faulted section make fault location accurately. It overcomes the difficulty of radial power distribution systems fault location. Through simulating for the IEEE 13 node test feeder with different faults, including various fault resistance, loading variation and the connected distributed generation, it proves the method’s accuracy and effectiveness.
Authors: Li Pin Chen, Xian Yong Xiao, Ying Wang, Jian Jiao
Abstract: When faults happen to the power system components, the duration of voltage sags is determined by the cooperation of protection system. Many literatures have been done in analyzing the factors which influence the magnitude of voltage sags, but the impact of protection cooperation on sag duration is not considered by existing studies. In order to estimate the duration of voltage sags more precisely, the novelty of the proposed approach is in probabilistic modeling of the cooperation of the protection system using the concept of Markov state space, then voltage sag frequency and sensitive equipment trips considering protection cooperation can be estimated by utilizing the configuration and setting value of the protection system. The proposed method was applied to the IEEE 57-bus test system, and the simulation results show that the proposed method is practical, simple and adaptive.
Authors: Zhuo Lin Zeng, Xian Yong Xiao, Ying Wang
Abstract: In order to depict the complex uncertainty involved in evaluation of equipment sensitivity to voltage sags, the voltage tolerance level of sensitive equipment is characterized by interval data, a evaluation model is proposed to derive interval probabilities of equipment operation status. Hybrid entropy is used to measure the uncertainty of randomness and fuzziness. Then, the interval result is transformed into point-valued probability based on maximum hybrid entropy model. By the help of personal computers, the proposed model is finally verified in a test distribution system.
Authors: Hao Li, Xian Yong Xiao, Ying Wang
Abstract: It is difficult to assess the impact of voltage sags on sensitive equipment because of the complex uncertainties involved in voltage tolerance capability. Determining the distribution regularity of voltage tolerance capability is an important step in voltage sag sensitivity assessment. Computers’ voltage tolerance capability are obtained through laboratory tests. The point-value distribution function of voltage tolerance capability is calculated by Maximum Entropy Principle and then the interval probability distribution function is derived based on confidence interval, so as to derive an interval probability of equipment failure probability. The proposed model is finally verified in the IEEE-30 bus system. The results are compared with that of stochastic estimation method, showing that the proposed method can reflect actual conditions better and obtain accurate result.
Authors: Jing Feng, Xian Yong Xiao, Chao Ma
Abstract: The risk assessment incorporate the severity as well as the possibility of event, however synthetic severity index weight coefficient is setting up subjectively in existing catastrophic event risk assessment. To overcome the uncertainty of the weight setting in conventional synthetic risk assessment, this paper introduces the entropy method to determine the weight objectively. Based on the existing severity measure matrix, the weight coefficient of severity indicator is generated by the entropy weight method combined with fuzzy membership function, furthermore proposing a catastrophic event assessment mathematical model and method based on uncertainty. The simulation of the local power grid proved that the proposed method is with correctness and objectivity, provided with engineering value.
Authors: Jing Feng, Ying Wang, Xian Yong Xiao
Abstract: The synthetic risk assessment method incorporating the severity and the possibility is used to identify the catastrophic event sequences in power system. The weight setting of each severity index is determined by the proposed entropy weight method. Comparing with traditional methods, the entropy weight method can determine the weight coefficients objectively. The simulation results for the WSCC-9 buses system have proved the validity of the proposed method. This method can be used in the practice power system.
Authors: Wen Hai Zhang, Jian Wen Yang, Xian Yong Xiao, Ying Wang
Abstract: When single-line-to-ground fault happen in neutral non-effectively earthed system, there is a big difference between the fault feeder and un-fault feeder in transient signal energy centralized frequency band and signal amplitude of fault phase. The transient signal energy in fault feeder’s fault phase is bigger, and it centralizes in lower frequency band. But the transient signal in un-fault feeders’ has the contrary features. And this feature is affected little by the fault initial angle. So the paper proposed a method that using the gravity frequency and transient signal energy to form a two-dimension line selection method that using the signal overall distribution characteristics. It can be applied in neutral unearthed and resonant system simultaneously. And the method is effectively to different fault initial angle and fault resistance. The method is proved correctly, effectively and adaptively by actual simulation in different fault cases.
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