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Zhang L.Y.,Sichuan University | Xiao X.Y.,Smart Grid Key Laboratory Of Sichuan Province
Applied Mechanics and Materials | Year: 2013

The necessity of research on the vegetation-related failure and its inherent hidden timescale in the cascading failures is attached importance based on the facts of recent blackouts internationally. The dynamic behavior of line sag and the vegetation growth are modeled. The time of vegetation related failure after step increase of the line current due to other disconnect events is calculated considering specified physical circumstances, and it can help operators be aware of the necessary urgency of system crisis. Case studies are made on WSCC-9 and IEEE-24 test system respectively, and the results show the method proposed is able to identify collapse sequences due to vegetation-related failures and corresponding timescales, and make great contribution to the prediction and prevention of cascading failures. © (2013) Trans Tech Publications, Switzerland.

Yang D.,Sichuan University | Wang Y.,Smart Grid Key Laboratory Of Sichuan Province | Xiao X.,Smart Grid Key Laboratory Of Sichuan Province
Applied Mechanics and Materials | Year: 2013

Considering the complicated uncertainty of the occurrence of equipment failure and the serious level of its sequence due to voltage sags, this paper classifies the invalided samples into three categories. The corresponding uncertainty is measured by random entropy, fuzzy entropy and cross entropy respectively. A maximum hybrid entropy assessment model is proposed. Based on the quantitative assessments of equipment invalidation rates, the comprehensive assessment is carried out according to the corresponding weight. Compared with existing methods, the proposed method is able to overcome both over- and under-estimation problems, with the results in line with practice very well. © (2013) Trans Tech Publications, Switzerland.

Zhang L.,Sichuan University | Ding L.,Sichuan Electric Power Research Institute | Xiao X.,Sichuan University | Xiao X.,Smart Grid Key Laboratory of Sichuan Province | And 2 more authors.
Advanced Materials Research | Year: 2012

A method was proposed to throw light on the initial period of cascading failure that would be the best time to implement prediction and prevention. A more accurate hidden failure model which considers fault locations and protection schemes was created, as well as a conductor temperature-outage probability model depicting tree-to-line contacts happened in the blackout frequently. It reveals the physical process of cascading failure more clearly and demonstrates that differently located fault which may trigger different PEFD of hidden failures and different ambient situations can both result in different outage sequence. © (2012) Trans Tech Publications.

Li Z.,University of Sichuan | Li Z.,Smart Grid Key Laboratory of Sichuan Province | Yang H.-G.,University of Sichuan | Yang H.-G.,Smart Grid Key Laboratory of Sichuan Province
Dianli Xitong Baohu yu Kongzhi/Power System Protection and Control | Year: 2012

The power supply of regional power grid is a substation that connects the upper and lower grid. REI equivalent is applied to solve the problem of slack node selection in voltage and reactive power optimization control in regional power grid. Taking into account the difficulty of getting the upper grid operating parameters, varying-intercept linear regression method is proposed to obtain equivalent parameters according to local data, in which valid sample points are obtained through fluctuation filter and vector translation transformation and analyzed by time-weighted regression method. Case analysis show that without the information of the upper grid, this model can reflect the characteristics of voltage and reactive power of the boundary bus, enable the lower grid to regulate the voltage of the boundary bus, and make the calculated voltage of the whole grid more accurate. Compared with conventional model, this model only adds a node in optimization calculation, so it's simple and practical.

Guo X.-M.,University of Sichuan | Guo X.-M.,Smart Grid Key Laboratory of Sichuan Province | Liu J.-Y.,University of Sichuan | Liu J.-Y.,Smart Grid Key Laboratory of Sichuan Province
Dianli Xitong Baohu yu Kongzhi/Power System Protection and Control | Year: 2011

Power disaster-relief resources allocation schedule, as an important part of an Emergency Command Decision Assistant system, plays an important role in response to sudden power failures caused by external factors. Based on the characteristics of demand for power material, the paper makes full use of the information connected to grid emergency command system. In order to search for the best logistics path, symmetric triangular fuzzy numbers is used to simulate the uncertainties in emergency logistics. The order of power restoration is established to greatly enhance the stability margin of the grid and reduce the outage cost. On this basis, power disaster-relief resources allocation schedule is established considering the guarantee rate. An example proves the efficiency and validity of the approach.

Zhao H.,University of Sichuan | Xiao X.,University of Sichuan | Xiao X.,Smart Grid Key Laboratory of Sichuan Province | Li Z.,Chengdu Electric Power Bureau | And 2 more authors.
Dianli Zidonghua Shebei/Electric Power Automation Equipment | Year: 2011

According to the transition process of equipment fault status, all kinds of status excluding normal and complete fault status are considered as incomplete fault status and the possibility of equipment failure due to voltage sag is evaluated. The voltage tolerance level of sensitive equipment is characterized by the interval data and, combined with the randomness of voltage sag, the interval possibility of incomplete fault status is determined. To more comprehensively take the complexity and uncertainty into account, the hybrid entropy is used to measure the randomness and fuzziness of practical voltage sag and the model of maximum interval hybrid entropy is developed to estimate the equipment sensitivity under certain conditions and to obtain the point probability of equipment failure rate. Comparison with the measured data of personal computer failure rate due to voltage sag shows that, the results in small samples are quite accurate. The simulation for IEEE 33-bus system proves the effectiveness of the introduced method.

Li H.-Q.,Sichuan University | Li H.-Q.,Smart Grid Key Laboratory of Sichuan Province | Xiao X.-Y.,Sichuan University | Xiao X.-Y.,Smart Grid Key Laboratory of Sichuan Province | And 2 more authors.
International Journal of Electrical Power and Energy Systems | Year: 2011

The existing problem with probability evaluation of sensitive equipment failure arising from voltage sags is how to measure the uncertain properties and determine the mathematical models of influencing factors. In this paper, the uncertain properties of voltage sags, voltage tolerance of sensitive equipment, and equipment operation states are explored. The intension and extension uncertainties of influencing factors are used to distinguish the mathematical properties. Stochastic and fuzzy variables are introduced to quantify these uncertainties. The corresponding models are proposed. A multi-uncertainty evaluation method of sensitive equipment failure probability is presented also. With the proposed method, the maximum entropy method is used to extract the probability distribution of voltage sag intensity while the determination principle of membership function of fuzzy safety event is applied to determine the multi-uncertainty evaluation model. As a case study, a personal computer is simulated. The results show that the proposed method is feasible and effective, and can be deployed in other fields. © 2010 Elsevier Ltd. All rights reserved.

Huang Y.,University of Sichuan | Huang Y.,Smart Grid Key Laboratory of Sichuan Province | Liu J.,University of Sichuan | Liu J.,Smart Grid Key Laboratory of Sichuan Province | And 4 more authors.
Dianli Xitong Zidonghua/Automation of Electric Power Systems | Year: 2012

A battery model is developed. The scale effect of electric vehicle centralization is analyzed and a framework of centralized electric vehicles taking part in vehicle to grid is described. By developing the load frequency control model for electric vehicles participation, the role and effect of the control model is studied. The simulation results show that, as a type of mobile battery energy storage facility, electric vehicles can provide faster system reserve by effective controlling. © 2012 State Grid Electric Power Research Institute Press.

Chen L.-P.,University of Sichuan | Xiao X.-Y.,Smart Grid Key Laboratory of Sichuan Province | Zhang Z.,Yibin Electrical Power Bureau | Wang Y.,University of Sichuan
Dianli Xitong Baohu yu Kongzhi/Power System Protection and Control | Year: 2013

In order to depict the duration of voltage sags more precisely, the time characteristic of protection system is taken into consideration, which influences the duration of voltage sags obviously. Based on the traditional model for voltage sags frequency assessment, the mapping relationship between voltage sags duration and frequency is established using the method of fault positions, which can reflect the actual process of the protection operation. The proposed method is applied to the IEEE 30-bus test system, and the simulation results show that the time characteristic of protection system has an obvious effect on voltage sags frequency assessment, and neglect of the time characteristic of protection system would result in large error. The proposed method is simple, adaptive and practical, and it is of academic value and practical foreground.

Huang J.,Sichuan University | Xiao X.-Y.,Sichuan University | Xiao X.-Y.,Smart Grid Key Laboratory of Sichuan Province | Liu X.-N.,Sichuan University
Dianli Xitong Baohu yu Kongzhi/Power System Protection and Control | Year: 2012

Considering the integrity and strong relevance of each point in short-term daily load value, the paper proposes a new model exposing and forecasting the daily load as a whole. We consider the 24 daily load values as a 24-dimensional data set, study the complex load changing rule from the multi-dimensional perspective and establish a high-dimensional load forecasting model. We use manifold theory to make an effective dimension reduction of the high-dimensional model, thus extract the inherence characteristics and overall regularity of the high-dimensional data, revealing the useful information it contains. We adopt locally linear embedding (LLE) to make a nonlinear dimension reduction for the 24-dimendional load data, and forecast the load in low dimensionality space, and then reconstruct the 24 load prediction based on the LLE reconstruction algorithm. Simulation results show that the proposed model performs better than those component predictions.

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