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Liao Z.,South China University of Technology | Yue L.,Zaozhuang Power Supply Company | Wen F.,Zhejiang University | Huang S.,South China University of Technology | Li S.,South China University of Technology
Dianli Xitong Zidonghua/Automation of Electric Power Systems | Year: 2013

Most existing power system fault diagnosis methods employ the state information of protective relays and circuit breakers, while the time sequencing information of alarm messages has not yet been fully used. As the result, definite fault diagnosis results cannot always be achieved especially for complicated and multiple faults with information missing and/or distorting, and sometimes it may result in false fault diagnosis. Under this background, a hybrid rule network based power system fault diagnosis method is developed. First, the largest sets of fault hypotheses are generated by establishing rule networks for various components. Then, a fault hypothesis authentic assessment model employing the time sequencing information of alarms is developed so as to determine the fault components and identify the causes. The developed method can fully use the digital information from sequence of events (SOE) and the analogue information from fault recorders, as well as use the cause-effect relationships and time sequencing information of alarms, so as to effectively improve the fault-tolerance capability of the fault diagnosis method. Finally, a practical fault scenario is served for demonstrating the feasibility and efficiency of the developed fault diagnosis model and method. © 2013 State Grid Electric Power Research Institute Press.

Xia W.H.,Shandong University of Science and Technology | Xia W.H.,Zaozhuang Power Supply Company | Gong M.F.,Shandong University of Science and Technology | Li G.L.,Shandong University of Science and Technology | And 3 more authors.
Advanced Materials Research | Year: 2013

Aiming at the problem that Current Transformer (CT) affects differential protection, this paper proposes a new method to identify CT saturation based on Empirical Mode Decomposition (EMD). Differential current can be decomposed into few Intrinsic Mode Functions (IMFs) by EMD. When CT is linear transfer, the current waveform is nearly a sine wave, and it only contains one dominant IMF. However, CT saturation leads to the distortion of secondary current which contains at least two dominant IMFs. From the defined projection area on t-axis of each IMF and the specific gravity coefficient, the number of dominant IMF can be got. Thus CT saturation can be identified. Theoretical analysis and simulation results show that this method can identify CT saturation of different degree. It is convenient to achieve and hardly to be affect by aperiodic component. © (2013) Trans Tech Publications, Switzerland.

Qi Z.,North China Electrical Power University | Zhang S.,Zaozhuang Power Supply Company | Yang K.-Z.,Electric Power Development Co.
Dianli Xitong Baohu yu Kongzhi/Power System Protection and Control | Year: 2010

Due to the large amount of branches and high grounding resistance of distribution grid, the grounding fault location in 10 kV system has not been solved effectively. The grounding fault location technology in 10kV system is proposed by combining voltage-time line sectionalizer and AC signal method. Firstly, the grounding fault is isolated by line sectionalizer, so that the fault is located and the influence caused by distributed capacitance is weakened. Then 60 Hz AC signal is injected at the fault area, and the signal can be measured so as to find the exact location of grounding fault. To avoid the influence of distributed capacitance to AC injection signal, the calculation method of optimal length of isolation area is intensively studied. The correctness and feasibility of this technology has been fully proved by site experiments.

Gong M.-F.,Shandong University of Science and Technology | Xia W.-H.,Zaozhuang Power Supply Company | Zhang X.-M.,Jinan Power Supply Company | Li G.-L.,Zaozhuang Power Supply Company
Dianli Xitong Baohu yu Kongzhi/Power System Protection and Control | Year: 2013

Aiming at the problem that CT saturation will affect transformer differential protection's accuracy and speed, this paper proposes to use Hilbert Huang Transform (HHT) to identify transformer fault under CT saturation condition. The waveform of transformer's external fault current contains some catastrophe points; in contrast, internal fault current's waveform is continuous. The new method is just based on this waveform characteristic. Firstly, a group of intrinsic mode functions (IMF) which are different in characteristic scale are obtained from Empirical Mode Decomposition (EMD). Then, Hilbert transform is applied for the first decomposed IMF to get the instantaneous frequency. Instantaneous frequency's catastrophe points just reflect current's catastrophe points. According to time interval between the two adjacent catastrophe points, it can identify transformer's external fault, internal fault and transferring fault accurately. PSCAD simulation results verify that under CT saturation condition, this method can identify all kinds of faults of transformer in 12 ms. Besides, it can block the inrush current.

Chen F.,University of Jinan | Zhang L.,Shandong University | Han X.-S.,Shandong University | Zhang P.,Zaozhuang Power Supply Company | Wang C.-Y.,Zaozhuang Power Supply Company
Dianli Xitong Baohu yu Kongzhi/Power System Protection and Control | Year: 2014

To solve existing problems for evaluation of distribution line loss and the related improvement measurement, this paper presents a probabilistic algorithm, which is used to evaluate the loss reduction strategy. In view of lack of real-time data about distribution network, firstly, the distribution loads are classified by their characteristics, and the same class loads have similar power curve. The loads obtained are assigned by power curve and energy supply. Then, all of load data are revised by matching power flow and data under typical data. Based on above-mentioned, the mathematic distribution character of line loss with load fluctuation is calculated by Monte Carlo simulation method, which is the basis for evaluation of loss reduction. The validity and efficiency of the proposed method is testified by real-time data of 10 kV distribution line at somewhere in Shandong Province.

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