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Chen J.,XJ Electrical Co. | Zhang Y.,XJ Wind Power Technology Co. | Deng M.,XJ Electrical Co. | Yao D.,XJ Electrical Co.
Dianli Xitong Baohu yu Kongzhi/Power System Protection and Control | Year: 2016

To solve the problem of transformer differential protection refusing action, when outside fault CT saturation transfering the same phase inside fault with CT saturation, this paper puts forward a scheme based on differential current sampling points differentia saturated open. For a single power supplying when differential current sampling points of CT saturation periods will be small or presenting interruptive angles; if multiple power supplying and single CT saturation, differential currents return to normal waveforms. It uses ratio braking relations of differential current sampling point and characteristics of the braking current interruptive angle, by identifying total sampling points of meeting ratio braking characteristics and interruptive points within a cyclic wave, to judge whether the fault in the area. The simulation results show that this method is suitable for the identification of the same phase fault about transformer differential protection. © 2016, Power System Protection and Control Press. All right reserved. Source


Li W.,Harbin University of Science and Technology | Tong S.,XJ Wind Power Technology Co. | Cheng P.,Harbin Engineering University
Zhongguo Dianji Gongcheng Xuebao/Proceedings of the Chinese Society of Electrical Engineering | Year: 2010

Taken a 400 W off-grid type permanent magnet synchronous generator as an example, the 2-D model of electromagnetic field was established. By using the field-circuit coupled method, the electromagnetic parameters of prototype with different loads and speeds were calculated. Based on the original structure design of prototype, two kinds of rotor structures were proposed and compared in terms of the no-load leakage coefficient, anti-EMF waveforms and the harmonic content of air-gap flux density; and the influences of these two structures on the electromagnetic performance of generators were analyzed. According to the heat transferring theories, the heat losses evaluated by the electromagnetic analysis were taken as the distributed heat sources; and the 2-D calculation model of temperature field for the whole area was built. The relationship between wind speed, load and temperature distribution, through calculation and analysis of temperature field under different wind speed and load conditions, can be gained. Electromagnetic and thermal performance tests were studied; and it was showed that the test values were almost equal to the calculated ones, so some useful conclusions can be drawn to provide support for design and optimization of the off-grid type permanent magnet synchronous generator. © 2010 Chinese Society for Electrical Engineering. Source


Cheng H.-B.,XJ Wind Power Technology Co. | Yuan W.,XJ Wind Power Technology Co. | Zhou W.-B.,XJ Wind Power Technology Co. | Xu J.-G.,XJ Wind Power Technology Co. | Lu R.-B.,XJ Wind Power Technology Co.
Dianli Xitong Baohu yu Kongzhi/Power System Protection and Control | Year: 2013

Advantages and disadvantages of all kinds of LVRT topological structures and the control strategies applied in the current DFIG are discussed, and the new LVRT scheme different from the Crowbar technology is presented. On the basis of analyzing the new LVRT topological structures of DFIG with DBR circuit topology as well as the effect of the DBR circuit during grid voltage dip, the mathematical models of the equivalent circuit of DFIG power system during normal voltage and grid voltage dip are established. Through analyzing the mathematical models, the control mode of LVRT is presented. At last, the experimental waveforms are analyzed at the WEC rate power output while under 20% balanced and unbalanced voltage dip respectively on the new LVRT topology, and it is fully verified that the DBR strategy is feasible. Source

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