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Xue M.,Shanxi Electric Power Research Institute
Applied Mechanics and Materials

This paper proposes the modle based on Grey system theory to evaluate conditions of transformer. The model of unequal-interval GM (1,1) and GM(1,1) model including buffer operator are established to predict the values of gas dissolved in oil of transformer. According to the results of prediction,state of power transformer will be divided into five categories in order to propose corresponding repair strategy.The method is effective on providing support for transformer condition maintenance.The proposed method has been verified by the experimental data. © (2014) Trans Tech Publications, Switzerland. Source

Wang X.,Tianjin Electric Power Research Institute | Lin J.,Tongji University | Li S.,Shanxi Electric Power Research Institute | Zheng W.,State Grid Corporation of China
Dianli Xitong Zidonghua/Automation of Electric Power Systems

Islanding operation is a special operation mode in the smart grid. For a power transmission system, if a connected system is split into several stable islanding sub-systems in time in the optimal islanding operation mode in case of extreme emergency, not only will enormous losses due to large area blackout or even system collapse caused by the spread of the local fault be avoided, but the amount of load shedding and generator tripping might be minimized as well. For a distributed system with distributed generator (DG), optimum islanding operation can bring the potential of DG into full play, while improving the reliability of power supply. The influencing factors of the optimal island partitioning in the smart grid are summed up and all the relevant methods and strategies available at home and abroad are thoroughly analyzed and classified. And the advantages and disadvantages along with key issues of each method are also discussed. Finally, the development tendency and the problems demanding prompt solution are treated. © right. Source

He W.F.,Xian Jiaotong University | Dai Y.P.,Xian Jiaotong University | Wang J.F.,Xian Jiaotong University | Li M.Q.,Xian Jiaotong University | Ma Q.Z.,Shanxi Electric Power Research Institute
Applied Thermal Engineering

The performance of air-cooled steam condensers (ACSCs) is always influenced under the unfavorable effect of wind conditions. It is significant to understand the mechanism of such influences so as to improve and optimize the performance of the condensers. In this study, the flow field around a 2 × 600 MW direct air-cooled power plant at different wind speeds and ambient temperatures is numerically simulated, and the relevant influence mechanism is illustrated. User defined function (UDF) based on steam properties, which plays a critical role in the prediction of condenser back pressures, is proposed to simulate the condensation of the turbine exhaust in the exchangers. It is found that wind speed has great influences on the performance of air-cooled steam condensers due to the variation of pressure distribution around the ACSC platform. Heat transfer rate degrades rapidly, while the fan flow rate rises slightly, with the increase of ambient temperature because the heat transfer potential between ambient air and the turbine exhaust is determined by their temperature difference. Finally, the stable back pressures corresponding to each prescribed wind condition are forecasted according to the comparison between the computational heat transfer rate and the ideal heat rejection. © 2012 Elsevier Ltd. All rights reserved. Source

Jing M.,Shanxi Electric Power Research Institute
Dianli Xitong Zidonghua/Automation of Electric Power Systems

Positive-sequence polarized voltage of distance relay is discussed with voltage phasor diagram method. The phase angle variation of bus voltage and bus positive-sequence voltage before and after the various asymmetrical faults for long-distance and heavy-load lines are analyzed and compared. The bus positive-sequence voltage is adopted as polarized voltage of distance relay, which can effectively reduce and avoid overreach of distance relay when the grounding fault via fault resistance occurs near the setting point of the distance relay. ©2010 State Grid Electric Power Research Institute Press. Source

Chang X.,Shanxi Electric Power Research Institute
Dianwang Jishu/Power System Technology

Supercapacitor is a storage technology proposed as means of supplying short-duration transient energy. Inherent long time constant associated with supercapacitor means that this short-term energy transfer is inefficient. The proposed energy storage system combining supercapacitor and electrolytic capacitor is an improvement to supercapacitor based energy storage system with less volume, less cost and higher efficiency. Although the proposed system structure is simple with only two parallel capacitors, its performance relating to several parameters is improved. Based on constant current discharge mathematical model, relationship between the parallel system parameters and its performance are analysedand verified with experiment. It is shown that the parallel system improves energy transfer efficiency by 10% compared to supercapacitor system, and the efficiency can also be improved by adjusting certain parameters of the parallel system. ©, 2015, Power System Technology Press. All right reserved. Source

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