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Jiang J.,Chongqing University | Xu H.,Chongqing University | Zhang T.-Q.,Chongqing New Century Electrical Co.
Dianli Xitong Baohu yu Kongzhi/Power System Protection and Control | Year: 2014

Large capacity induction machines have a great influence on short-circuit current level of industrial distribution network. Accurate calculation of the feedback current plays an important role in protection configuration and short-circuit current calculation. The motor speed changing during voltage drop is an important factor affecting the accuracy of feedback current calculation, regardless of the speed changing may cause error in feedback current calculation and affect the operation of protection. Using the positive and negative sequence steady-state equivalent circuit of induction motor and constant complex coefficient linear differential equations solving process, forced component and free component of stator/rotor flux linkage are solved. Then the induction motor feedback current formula in consideration of speed changing factor is deduced. Furthermore, the influence of speed on each component of the flux and feedback current is analyzed. The correctness of the proposed analysis is verified by the fifth electromagnetic transient model of induction motor in PSCAD/EMTDC simulation software. ©, 2014, Power System Protection and Control Press. All right reserved.

Cai M.,Chongqing University | Tang K.,Chongqing University | Zhang T.,Chongqing New Century Electrical Co.
Dianwang Jishu/Power System Technology | Year: 2011

In allusion to the feature that non-linear load leads to haomonics, an equivalent load model in time domain is built. Under unknown load parameters at system side and consumer side, by use of physical relation between voltage and current at the point of common coupling (PCC) the load impedance is traced and identified by parameter indetification to locate harmonic source, meanwhile the quantized nonlinearity of current is led in to decide the responsibility to be borne by each consumer for the deterioration of power quality caused by harmonics. Simulation results show that the proposed method is simple and feasible and is not influenced by background harmonics.

Wang T.,Chongqing University of Posts and Telecommunications | Zhang D.-l.,Chongqing University of Posts and Telecommunications | Tao Z.-J.,Chongqing New Century Electrical Co. | Wang P.,Chongqing University of Posts and Telecommunications
Advanced Materials Research | Year: 2012

On the basis of in-depth study of the power system enterprise applications with distributed and heterogeneous characteristics, a solution to cope with an integrated data conversation platform is proposed against the background of power dispatching automation system which the data modeling and software component interface is not mature enough. This article also gives software design methods based on the CORBA specification and IEC 61970 standards for power system automation and elaborated the task execution flow of generic data access (GDA); at last corresponding test is also given. At the same time the development process for CORBA object services, resources sequence caching, distributed object calls and other important issues are given a detailed solution. © (2012) Trans Tech Publications, Switzerland.

Wang G.,Chongqing University | Jiang J.,Chongqing University | Tang K.-M.,Chongqing University | Zhang T.-Q.,Chongqing New Century Electrical Co.
Dianli Xitong Baohu yu Kongzhi/Power System Protection and Control | Year: 2010

Weighted least squares fuzzy support vector machines method is proposed for ultra-short-term load forecasting. In order to reflect the characteristic that the nearer data have a greater impact on the predicting value, the membership distribution of time domain is introduced in bi-direction, namely, transverse (output samples) and longitudinal (training samples). To overcome the disadvantage of predicting with a fixed coefficient, fast leave-one-out method is used to adaptively optimize the parameters on-line. The load data from a substation is used for simulating and the applications of different methods are compared. The results show that the proposed method can improve the forecasting accuracy compared with traditional methods.

Tang L.-J.,Chongqing University | Yu C.-Z.,Chongqing University | Zhang Q.,Chongqing University | Xiong W.,Chongqing New Century Electrical Co.
Dianli Xitong Baohu yu Kongzhi/Power System Protection and Control | Year: 2010

Limited by the techniques in the traditional protection device of under frequency load shedding(UFLS), the frequency change rate is always represents by an average value in a time segment. In order to put an end to the above phenomenon, the paper designs a sort of novel UFLS device based on MCF52235. By means of the module of DMA timer that owns input capture ability, the new device could capture the jump step pulse edge of the measured signal. Combined inner timer counter register with capture register, it could record the standard pulse number during a cycle. And by use of corresponding software algorithm, it could work out the measured signal's frequency and its change rate. Therefore the deviation resulted from average computing could be eliminated. The test result shows that the device can accurately act in time when the system frequency is reduced, and can effectively prevent wrong action of under frequency load shedding in abnormal cases.

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