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Fu X.,Xian Jiaotong University | Fu X.,Northwest Electrical Power Design Institute | Wang X.,Xian Jiaotong University
International Journal of Electrical Power and Energy Systems | Year: 2011

A computationally simple algorithm is developed for studying the load shedding problem in emergencies where an ac power flow solution cannot be found for the stressed system. The proposed algorithm is divided into two sub-problems: restoring solvability sub-problem and improving voltage stability margin (VSM) sub-problem. Linear optimization (LP)-based optimal power flow (OPF) is applied to solve each sub-problem. In restoring solvability sub-problem, rather than taking restoring power flow solvability as direct objective function, the objective function of maximization of voltage magnitudes of weak buses is employed. In VSM sub-problem, the traditional load shedding objective is extended to incorporate both technical and economic effects of load shedding and the linearized VSM constraint was added into the LP-based OPF. Case studies with a real 682 bus system are presented. The simulation results show that the proposed load shedding algorithm is effective, fast in finding the load shedding scheme to solve the problem of restoring solvability and improving VSM. © 2010 Elsevier Ltd. All rights reserved. Source

Qu G.-Z.,CAS Lanzhou Cold and Arid Regions Environmental and Engineering Research Institute | Zhang J.-M.,CAS Lanzhou Cold and Arid Regions Environmental and Engineering Research Institute | Cheng D.-X.,Northwest Electrical Power Design Institute
Yantu Lixue/Rock and Soil Mechanics | Year: 2011

To better understand the in-situ engineering conditions of frozen ground where the piers of Qinghai-Tibetan ±500kV Direct Current Transmission Line Project will be constructed; the direct shearing creep experiment for frozen silty clay, a kind of soil taken from Wudaoliang on the Qinghai-Tibetan Plateau and remodeled in different moisture contents and densities in laboratory at -2°C, was carried out. The study results show that most creep of the frozen silty clay appears as attenuation creep which has two phases: unsteady creep phase and steady creep phase; only several creeps of frozen silty clay takes on the third phases: accelerated creep phase. The long-term strength of frozen soil could be calculated by the long-term strength equation. The long-term strength of the frozen silty clay closely affected by the moisture content and density of the soil; the frozen soil with higher moisture content has higher long-term strength at low moisture circumstance; but it shows opposite trend at high moisture circumstance; the frozen soil with higher density has higher long-term strength with the same moisture content. Source

Huang J.,Xian University of Technology | Dang F.,Xian University of Technology | Guo C.,Northwest Electrical Power Design Institute
Modern Tunnelling Technology | Year: 2013

This paper quantitatively evaluates tunnel stabilit y using a safety factor defined in light of rock deformation and discusses the degree of stability by increasing the actual rock displacement caused by tunnel excavation to the ultimate displacement at the critical state. Based on the theoretical elasto-plastic analysis of an unlined circular tunnel, it derives a principle parameter reduction method in which the increase of actual displacement is achieved by considering the elastic modulus degradation of the surrounding rock. The safety factor is calculated by using the ultimate displacement as the criterion of tunnel instability. With the finite -element parameter reduction method, the stability of unlined circular tunnels with different depths and diameters in various grades of rock is discussed. The results show that the parameter reduction method is feasible and applicable to rock masses of grades I to IV, whereas there are some deviations for the rock mass of grade V. Source

Yang S.-B.,Northwest Electrical Power Design Institute | Xu X.,Tianjin Pipeline Engineering Group Co.
Yantu Gongcheng Xuebao/Chinese Journal of Geotechnical Engineering | Year: 2012

Based on the support system of deep foundation pit of Beijing Century Building with excavation depth of 19.95 m, the ground situation and surroundings as well as the situation of engineering geology are analyzed concretely. A comprehensive support plan combining the soil-nailing walls with pile-anchor system is proposed to make use of their respective advantages. The technique of artificial excavated piles is adopted to adapt to the cobble stratum so as to solve the problems aroused by power drilling. The maximum value of horizontal displacement is only 12.1 mm, and the mechanical properties of each support element are all in satisfactory. The results illustrate that the design is reasonable and the displacement of the pit is controlled effectively. The experience is valuable to similar projects. Source

Fu X.,Northwest Electrical Power Design Institute
Dianli Zidonghua Shebei/Electric Power Automation Equipment | Year: 2014

An algorithm of static security preventive control is proposed for power system with the consideration of uncertainty factors. A static security index of power system is proposed, which considers the probability of pre-defined contingencies and the uncertainty of load level. The preventive control strategy is obtained by adding the index into the preventive control model, which emphasizes the generator rescheduling and load shedding. For the large influence of load characteristics on system, the ZIP load model is adopted. The simulative result of a practical domestic system verifies its effectiveness. Source

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