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Cheng L.-M.,University of Sichuan | Li X.-Y.,University of Sichuan | Liu J.,Ertan Hydropower Development Company
Gaodianya Jishu/High Voltage Engineering | Year: 2011

The imbalance between electromagnetic torque and mechanical torque of each synchronous machine is the main factor which affects transient stability in the AC/DC transmission systems, and the DC power can be regulated rapidly. Thereby, combining the control of valve opening and DC power modulation, we proposed a coordinated control strategy to improve transient stability. According to the characteristic of system model, namely, a nonlinear system with multi-input and multi-output, the control strategy was designed based on feedback linearization of nonlinear system theory and optimal control theory of linear system. The validity of the coordinated control method was verified in a typical AC/DC parallel hybrid transmission system.

Xue Y.F.,Ertan Hydropower Development Company
Applied Mechanics and Materials | Year: 2013

Pre-estimate of hydropower project investment risks is of much importance because of the huge economic loss caused by the negative effects of the risk factors. Components of cash flow of hydropower project investment and finance evaluation are presented to study the effect of investment risk variables on hydropower project based on the structure of hydropower project investment and benefits. The project investment risk and index are evaluated by the simulation technique, which provides a basis for scientific decision-making of the project. © (2013) Trans Tech Publications, Switzerland.

Wu Y.,Tsinghua University | Liu S.,Tsinghua University | Zhang L.,Ertan Hydropower Development Company
Engineering with Computers | Year: 2011

This paper reports the simulation results for the unsteady cavitating turbulent flow in a Francis turbine using the mixture model for cavity-liquid two-phase flows. The RNG k-ε turbulence model is employed in the Reynolds averaged Navier-Stokes equations in this study. In the mixture model, an improved expression for the mass transfer is employed which is based on evaporation and condensation mechanisms with considering the effects of the non-dissolved gas, the turbulence, the tension of interface at cavity and the effect of phase change rate and so on. The computing domain includes the guide vanes, the runner, and the draft tube, which is discretized with a full three-dimensional mesh system of unstructured tetrahedral shapes. The finite volume method is used to solve the governing equations of the mixture model and a full coupled method is combined into the algorithm to accelerate the solution. The computing results with the mixture model have been compared with those by the single-phase flow model as well as the experimental data. The simulation results show that the cavitating flow computation based on the improved mixture model agrees much better with experimental data than that by the single-phase flow calculation, in terms of the amplitude and dominated frequency of the pressure fluctuation. It is also observed from the present simulations that the amplitude of the pressure fluctuation at small flow rate is larger than that at large flow rate, which accords with the experimental data. © 2010 Springer-Verlag London Limited.

Wang G.,Ertan Hydropower Development Company | Zhang J.-M.,Tsinghua University | Wei X.,Southwest Jiaotong University
Yantu Gongcheng Xuebao/Chinese Journal of Geotechnical Engineering | Year: 2011

Soil-structure dynamic response analysis in liquefiable soil is a difficult problem due to the difficulty of modeling the post-liquefaction behavior and the instability of numerical calculation. A cyclic elasto-plasticity model developed by the authors, which can describe the large strain behavior during an entire liquefaction process, has been implemented in a fully coupled finite element program. The seismic response of Daikai subway station subjected to the 1995 Hyogoken-Nambu Earthquake is investigated to illustrate the philosophy of soil-structure dynamic response analysis with emphasis on soil liquefaction and also to validate its effectiveness. The calculated stress-strain curves and effective stress paths of typical soil elements are given to reveal the relationship of the large lateral deformation of the station and surrounding soil with the liquefaction extent of sandy stratum. It is found that liquefaction-induced large deformation may be the main reason causing serious damage to the Daikai station during the earthquake.

Yu Y.,North China Electrical Power University | Wei C.,Ertan Hydropower Development Company | Zhu L.,Deyang Electrical Power Bureau
Dianli Xitong Baohu yu Kongzhi/Power System Protection and Control | Year: 2010

The paper adopts PSCAD/EMTDC software to establish the system model and simulates the impact of DC ground electrode current on transformers of different structures including group transformer, three-phase three pole transformer, and three-phase fineplole transformer, etc. The results show that because of the independent magnetic flux circuit and small reluctance, group-type transformer is most influenced by DC bias; three-phase three-pole transformer which has no DC circuit and has larger reluctance is least-affected by DC bias; three-phase five-pole transformer in which area of iron core is smaller than that of single-phase transformer is impacted between the former two even though having DC circuit.

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