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Nowadays great attention is paid to the problem of power quality. With the modern equipment, their operation is very sensitive to the quality of the power supply. When the power quality is not guaranteed, such as a nonstandard voltage, current or frequency, which will damage the equipment or the equipment will operate improperly. One of the basic problems here is Sag/Swells voltage. To solve this problem, the dynamic voltage Restorer (DVR) is put into use in the power distribution network. DVR will reduce or add the voltage in series with supply voltage through injection transformer to correct the amplitude, voltage phase and harmonic components into line. This paper proposes a control method for the DVR based on space vector control, with two feedback loops according to voltage and current. The authors use independent control methods, separation of components of direct and reverse in d-q Synchronous Reference Frame for DVR. This method has effectively controlled for the voltage sags and swells phenomenon in balanced and unbalanced. The research results are simulated and verified on Matlab - Simulink software.

We investigate the correlation of serum brain-derived neurotrophic factor (BDNF) level and its gene polymorphism with liver function classification in patients with hepatitis B virus (HBV) induced liver cirrhosis. A total of 182 patients with HBV induced liver cirrhosis were collected as a case group, and 186 healthy subjects in the same period were used as the control group. ELISA measured serum BDNF levels. Polymerase chain reaction-restriction fragment length polymorphism was used to detect rs6265 (A/G) and rs10835210 (A/C) in the BDNF gene. The serum BDNF level was significantly lower in the case group than in the control group. With the elevation of Child-Pugh classification in patients with HBV induced liver cirrhosis, the decrease trend of serum BDNF level was even lower. The difference in frequency distribution between the case group and the control group was statistically significant regarding GG, GA, and AA genotypes, as well as G and A alleles in rs6265 (all P < 0.05). The frequency distribution of genotypes and alleles of rs6265 was statistically different in HBV induced liver cirrhosis patients with different liver function grades (P < 0.05). In patients with HBV induced liver cirrhosis, the AA genotype of BDNF gene rs6265 had the lowest level of serum BDNF. Our study suggests that serum BDNF plays an important role in the grading and early diagnosis of liver function in patients with HBV-induced liver cirrhosis, and AA genotype at rs6265 of BDNF gene is a negative factor for liver cirrhosis. Moreover, the polymorphism of this locus could affect the serum BDNF level.

With the development of electric power industry, power cable will play a more and more important role not only widely used in distribution network, but also in the field of AC/DC and high voltage transimission system. Power cable is generally underground or underwater, the problem that fault concealment and long time troubleshooting make serious impact on the power supply reliability of power system. Evaluate real-time operation state of power cable by using multi-parameters from variety of monitoring and detection information, and strengthen early defect equipment monitoring on the basis of evaluation result, it can reduce equipment failure rate and prevent accident expanding and it has very important significance for improving power supply reliability, From the perspective of information fusion, the method of evaluation algorithm based on RBF (Radial basis function) neural network is proposed. Multi-parameter including online detection data, environmental factors, testing and equipment information is used to conduct a comprehensive evaluation on cable status. The method using data fusion in decision-making level by RBF neural network for results of different algorithms including catastrophe theory and ANP fuzzy theory can make up applicability problem of different evaluation algorithm, and achieve complementary functions between the algorithms. To further adapt to the actual conditions of parameters, the integrity of input parameters was associated to credibility of evaluation results, it will make evaluation results more complete. The affectivity of the algorithm was verified by practical data.

The paper presents a procedure for fault location in distribution network with only two-phase current transformers (TA), based on the use of the artificial neutral network (ANN). We constructed IA + IC as a new wave module to solve only two-phase current transformer which can not be zero sequence current situation, then traveling wave in the propagation characteristics of the bifurcation lines have been analyzed. Radiation network model is built and various fault conditions are simulated, the results showed: simulation results is consistent with analysis. Based on the theoretical analysis and simulation this paper selects the polarity of first three waves and their time difference as the input of artificial neutral network, fault zone detect first, fault distance locator next, then train and test the neutral network to establish fault diagnosis model. Using this model, fault zone and fault distance can be successfully identified. The model has been tested successfully on fault location in distribution networks with only two-phase current transformers.

Traveling wave consists of the frequencies ranging from tens of kHz to hundreds of kHz in distribution network with single-phase fault, S-transform is implemented to detect the fault line in distribution network from the tens of kHz high frequency transient component of the fault traveling wave. The moment depending on the maximum component in the highest frequency row of the S-transform magnitude matrix of zero modal bus voltage corresponds to the real mutation moment of zero modal bus voltage. Then the moment of the first fault traveling wave front is calibrated and recorded as the beginning moment of single-phase fault occurrence. At this moment, the phases of initial current traveling wave front detected by TA at the protection relay device between fault line and sound lines are opposite. The S-transform is implemented to fault zero modal currents. The argument difference of the highest frequency row between fault line and sound line is 180o after fault, which makes fault line detectible. The proposed method detects the phase characteristics of traveling wave signal from the level of relatively low high-frequency transient component, which can not only reduce the requirements of traveling wave acquisition and processing speed, but also enhance the capacity of high resistance tolerance and anti-noise ability. The simulation results verified the feasibility and validity of this method.

The conclusion draws from traditional power supplying capability evaluation method can not reflect the actual supplying capability of gridby quantitative index, so evaluating the overall power supplying capability by means of fuzzy method has its advantage. Fuzzy analysis method has been employed to create a city gridpower supplying evaluating model in respect of the reality of power supplying condition of KunMing network, in which weighting is assigned by effect value of data reflected by information entropy to avoid the influence of subjective elements in weighting assigning. Seven elements which reflect the power supplying capability of KunMing grid objectively and comprehensively have been chose to construct corresponding membership degree function curve according to their different reflecting dimensionalities of power supplying capability, then the membership degree value of each elements is deduced. Each of the seven evaluating elements is judged to obtain quantitative fuzzy evaluating results, and then these 7 elements are combined to judge the power supplying capability synthetically to derive the fuzzy evaluating result of power supplying capability of KunMing network.

In resonant grounded systems, when single phase-to-earth fault occurring, transient components of zero-sequence current in fault lines are composed of that in healthy lines. So there is a great difference between health lines and fault lines of transient information. This paper gives a new diagnostic method based on cluster. A cluster is an assemblage constituted by a set of objects with the character of similarity each other. But the objects in different clusters usually are not similar. In the process of cluster, the more similar the variables are, the more precedent they merged. Not more similar, merged later. The degree of similarity of different variables merged last is the lowest. When single phase-to-earth fault occurs, the transient information of zero-sequence current is seen as variables of cluster. A detecting criterion is built up by calculating and analyzing the statistics of cluster. The process of cluster can be shown though scatter plot and binary tree diagram. Simulation results show that the proposed method is convenient, symbolic and reliable.

The identification of shielding failure and back striking in transmission lines is always difficult. The process of back striking and shielding failure in UHVAC transmission lines was analyzed in this paper. Because the mechanisms of produced transient zero module current and its propagation paths were different between back striking and shielding failure, their wavelet energy of different frequency bands of transient currents were different. Thereby, from the perspective of protective relaying, this paper proposes an identification method to shielding failure and back striking in transmission lines based on wavelet transform. All data can be acquired from high speed relay protection device. And the results of PSCAD/EMTDC simulation show the effectiveness of the proposed method.

H. Rahman and B. H. Khan have given a new model for simultaneous AC-DC power transmission through a transmission line. This paper model formation to evaluate the reliability of main electrical scheme. Use advanced four state component model, redefined abnormal state and maintainable state, combined maintenance state based on condition of component and schedule maintenance state to maintenance state on the basis of taking account of the condition-based maintenance and then confirmed the conversion relationship and the parameter to each state. The main electrical scheme is simplified on the basis of function and gets more simple net. For DC station, it simplified with the method of combining components and dividing subzone. Apply advanced four state component model to make certain reliability parameters of each part and get reliability parameters of main electric scheme through Markov model.

The ultra high voltage current(UHVDC) is the important technical means for the solution of high voltage, large capacity, and long distance power transmission. ±800KV UHVDC transmission technology will be used in the project which transfer hydroelectric power in Yunnan Province and Sichuan Province to Guangdong Province and Shanghai and other east places in China. During the building course of double poles UHVDC system, one pole is often built up and run firstly, then the other pole is built and run. Even double poles are finished and run, if one pole defaults, the UHVDC system will run in single pole way. So single running way is common in UHVDC system, it is necessary to do some overvoltage research on UHVDC when the system runs in single pole way. The Yunnan Province to Guangdong Province ±800KV UHVDC system is taken as example to study the overvoltage, the single pole circuit of Yunnan Province to Guangdong Province UHVDC transmission system is given out, and the parameters of different electric equipments such as converter transformer, converter, electric line, reactor, filter are given out, too. Then this paper introduces some defaults which cause the overvoltage in UHVDC system, such as the AC defaults including three phases short circuit, two phases short circuit, one phase earthing and the DC transmission line default, the output breaker opening and so on. The PSCAD/EMTDC is used to simulate the UHVDC transmission system. Firstly, the model with PSCAD/EMTDC is built up, and then different defaults which cause overvoltage are simulated. The simulation result are given out and some useful conclusion are drawn in this paper.

In power system stability research, the coordinated control between PSS and FACTS is an important problem. The usually method is to apply genetic algorithm (GA) to optimize the parameters of them. The traditional GA has the merits of parallel algorithm, strong ability of global searching and sample programming. However, its hill-climbing ability is weak, and easily be convergence earier. Tabu search (ES) algorithm uses a flexible memory of search history to prevent cycling and to avoid entrapment in local optima. It has been shown that, under certain conditions, the TS algorithm can find global optimal solution. But the fatal fault of it is that the solution seriously depends on the initial condition. In order to eliminating the shortcomings of GA and TS, an improved genetic-tabu hybrid algorithm is proposed in the paper. The algorithm synthesizes the global search ability of GA and local optimization ability of TS, so improve the convergence and search rate. Simulation results show that the proposed control scheme provides good damping of electromechanical modes of oscillations and enhances power system stability with power angle and voltage.

Due to small grounding current and unstable electric arc at fault position, the faulty circuit selection in resonant grounded systems has always been a complex and difficult problem. This paper proposes a new diagnostic method based on the matter-element and correlation analysis of Extension Theory. The characteristics variables of zero-sequence current and the correlation function have been used to identify the correlation. With the results, we may select the faulty lines. In the new method, the weighting coefficient of fault characteristics is endowed with variance of correlation function. Which not only widening the gap between correlations but also erasing the influences of little current and the unstable electric arc. When the fault is in the short circuit, the method may erase the influence of capacitive current in normal long one too. Lots of digital simulation results show that the proposed method is effective and reliable.

This paper addresses the transient response of instant ground fault in Yun-Guang hybrid UHVDC/AC power transmission system. A detailed bipolar UHVDC electromagnetic transient model is established by PSCAD/EMTDC software. The control strategies for UHVDC system are investigated and the main factors of commutation failure are analyzed. A lot of simulation results demonstrate that Yunnan rectifier AC system fault can not cause UHVDC commutation failure. Metallic ground fault of Guangdong inverter AC system will result in UHVDC commutation failure but enough transition resistance can reduce the chance of it. When one pole ground fault of UHVDC line occurs, DC current of the fault pole has an obvious overshoot and non-fault pole is influenced a little. UHVDC can come back to normal operation once the instant ground fault is cleared.

Mid and long-term stability of complex power system is a most prominent problem which conventional transient simulation can not resolve. This paper analyzes the dynamic voltage stability of Yunnan power grid including plusmn 800 kV UHVDC transmission in 2010 by using full dynamic software. Full dynamic simulation is such a method in which the electro-mechanical transient, mid- and long-term dynamic simulations are organically unified. Gear method with variable step-size and order is applied to realize full dynamic simulation. Main models for dynamic voltage stability are presented. The influence of OLTC upon voltage stability at serious disturbance is investigated and the effectiveness of full dynamic simulation for dynamic voltage stability is verified. The results show that Yunnan main power grid is strong enough to keep stable at the assumed serious fault, but 500 kV OLTC automatic regulation post fault may result in voltage instability if system has not enough reactive power reserved.

The classical four-state component model haven't accord to practical situation because the equipment repairing technique based on condition of component developed quickly, and this paper put forwarded an advanced four state component model. That model redefined abnormal state and maintainable state, combined repair state based on condition of component and schedule repair state to repair state and then confirmed the conversion relationship and the parameter to each state. This paper put forwarded combining components and dividing subzone method to simplify the main electrical scheme to be a simple directional network, applied advanced four state component model in that network to calculate the subzone's reliability parameter. Applied the least path searching method to search the least path matrix for the network and predigested the method by matrix multiplication, enumerated each fault state of that network by analytical method, worked out the reliability index of that network by VC++. And the reliability index of network is the reliability index of main electrical scheme in ChuXiong plusmn800 kV rectifier station. At last this paper analyzed the result of main electrical scheme's reliability and it proved the method's validity which used in this paper.

A new integrated fault line detecting method using extenics is proposed, for existing methods of fault line detection are affected by fault switching angle and electric arc etc., the accuracy of fault line detection is not satisfied. Three factors of matter-element in single-phase fault line detection are confirmed, which are the possible fault line's aggregate and its correlative characteristic aggregate and quantity field with the stated characteristic. The characteristic aggregate includes the decaying direct current component, the D-value of transient energy, the D-value of reactive power and the correlation coefficient. The relation function of extended aggregate is imported, in order to quantificationally calculate the fault degree of each line and confirm the corresponding weight function. Then, the fault line detection is realized. The method integrates four algorithm. It can eliminate not only the effect of the small current of fault line and the unstable grounding electric arc, but also the effect of the capacitance current of the long sound lines when the short line is fault. The method is not affected by the uncertain factors such as the fault switching angle, transition resistance. Large simulations indicate that the fault line detecting method is correct and reliable.

As one of the most important equipments to guarantee power gird operating safely and stably, the fault diagnosis of transformer has most important sense. Since the general diagnosis methods such as DGA and attributes' reduction of rough set haven't enough precision for transformer's fault diagnosis, Extenics and rough set theory are brought into diagnosing the fault of transformer. Using attribute predigesting method in rough set theory to classify the attribute term which needed by each fault diagnosis. Then building matter element model for transformer's fault diagnosis. Using DGA testing datum to be attribute set and the transformer's standard fault model to be the decision set for transformer's fault diagnosis. Utilize association function from Extenics to count each fault degree. Define the fault accepting rule to get transformer's fault. Use this method to diagnose one fault transformer and the diagnosis result matched case of fact fault. Apply this method to diagnose 76 DGA testing data and the right ratio of diagnostic result is better than IEC method.

The ultra high voltage direct current(UHVDC) is the important technical means for the solution of high voltage, large capacity, and long distance power transmission. plusmn 800 KV UHVDC transmission technology will be used in the projects which transfer hydroelectric power in Yunnan Province and Jingshajiang river to Guangdong Province and Shanghai and other places in China. Along with the rapid development of UHVDC in China , how to improve the security and reliability of the running of UHVDC system has become an urgent thing. Travelling wave protection is the main protection for HVDC link. So it is necessary for us to study Travelling wave protection for UHVDC link. In this paper, the circuit of UHVDC transmission is given out. The parameters for different electric equipments, such as converter transformer, converter, electric line, reactor, filter are given out. The travelling wave protection theory is discussed in this paper,too. The PSCAD program is used to simulate the UHVDC transmission system. We have the simulation result and draw the conclusion in this paper.

UPQC is a powerful application to settle the Power Quality problem. The DC voltage being the given value is the prime of its correct and valid working. The principle and the advantage of PilambdaDmu controller are presented in this paper. By using the software MATLAB and EMTDC/PSCAD, the PilambdaDmu controller and the UPQC are simulated separately. The PilambdaDmu control of the DC voltage is the utilized through the interface of the MATLAB and EMTDC/PSCAD software. Simulation results show the validity and correctness of the PilambdaDmu controller and it is advantaged than the traditional PI control. The PilambdaDmu controller would be widely used in Power System and other systems.

This paper introduce a method of enlarging power transfer capability of electric power corridor connecting to different regions by means of compensation. Different from traditional way to consider voltage stability condition, this paper focus on the influence caused by power transferred in corridor, and this make developing new tool of analysis necessary. A new modified continuous power flow calculation method is developed in this paper, sensitivities of voltage to power transferred is used to determine the site of Var compensation and optimal algorithm of predictor corrector Interior point method is employed to optimize total injection of reactive power in selected weak buses.

In this paper, it takes the existing experimental electric power transmission price mechanism to the large power consumers of China as basis, combining the operation status of power market of Yunnan province with the power consuming status of the high energy-consuming enterprises, and then establishes profit model of triple sides, including power plants, power network corporations and large power consumers, under both "network purchasing" and "direct purchasing" mode. Through comparison to the profit of triple sides under both models, the essential conditions to implement the direct power purchase between power venders and vendees are presented, and then the advantages and disadvantages of the electric power transmission price mechanism are gotten out. In this paper, it takes the Yunnan Aluminum Industry Co. Ltd. as an example of direct power purchasing mode to calculate and analyze, and finally gives a "three-wins" program of the power plants, power network corporations and large power consumers, which provides a feasible foundation for establishing the direct power purchasing experiments of large power consumers in Yunnan province.

The reliability can be enhanced by using single-phase reclosing, but when reclose to permanent faults, it is another surge on system. So there is necessity to study on the influence of reclosing sequence on transient stability margin. In the case that transient and permanent fault is not effectively identified, the influence of sequence and time of single-phase reclosing on transient stability margin in Southern China Power Grid of 2005 year is studied using software FASTEST when single-phase fault is occurred on 500 kV Anshun - Tianshengqiao transmission line in this paper. Simulation results indicate that when the terminal without fault uses non-voltage detecting and recloses first instead of the two terminals use non-voltage detecting in turn, the transient angle, voltage and frequency stability margin can all be enhanced and the working condition of breaker can be improved. A method combined with fault location algorithm to modify the sequence of single-phase reclosing online to enhance transient stability and lower the surge when reclose to permanent fault is proposed.

The reliability can be enhanced by using single-phase reclosing, but when reclose to permanent faults, it is another surge on system. So there is necessity to study on the influence of reclosing sequence on transient stability margin. In the case that transient and permanent fault is not effectively identified, the influence of sequence and time of single-phase reclosing on transient stability margin in Southern China power grid of 2005 year is studied using software FASTEST when single-phase fault is occurred on 500 kV Anshun-Tianshengqiao transmission line in this paper. Simulation results indicate that when the terminal without fault uses non-voltage detecting and recloses first instead of the two terminals use non-voltage detecting in turn, the transient angle, voltage and frequency stability margin can all be enhanced and the working condition of breaker can be improved. A method combined with fault location algorithm to modify the sequence of single-phase reclosing online to enhance transient stability and lower the surge when reclose to permanent fault is proposed. (4 pages)

This paper is concerned with sympathetic interaction between two transformers caused by inrush transients in order to discuss whether the existing inrush current identification algorithms are applicable to sympathetic inrush. Based on models of two transformers in parallel and in series operation, the influencing factors such as system resistance, switching time, residual flux and the load of a connected transformer are investigated. Then the inrush current identification algorithms including the scheme of second harmonic restraint, dead angle restraint and waveform symmetry principle are used to test their validation under various conditions of the transformer sympathetic inrush. It is believed that the study will provide a theoretical basis to improve the principle of transformer protection and then reduce the possibility of mal-operation of relays. (6 pages)

While a faults at the terminal of a line, the reflection of travelling wave is complex and the polarity of forward and backward current travelling wave may be different. In this condition, the fault location results of faulted lines and fault-free lines are same. Therefore, the protections based on polarity comparison and travelling wave fault location will mal-operate. According to the theory of travelling wave reflection and refraction, if the transmission line is fault-free, the forward travelling wave will be reflected only at the terminal of lines, and the reflect coefficient of current travelling wave is -1. Whereas the forward travelling wave will be reflected at the fault points when switching onto faulted line, and the reflect coefficient of current travelling wave is not equal to -1 whether the faults at the middle or at the terminal of lines. Based on the theory described above, a new closing protection is presented. The principle of proposed protection can ensure that the relays will operate correctly in any case, and the results of tests show that this method is reliable and effective. (5 pages)

UPQC is the powerful tool to settle the power quality problem. This paper presents a novel control strategy of UPQC. It can be used in the system that voltage and current are unbalanced or/and with harmonics. Only the voltages and the currents measured are used in the control, it avoids the transformation like Park transformation of dq0 theory which is based on the instantaneous reactive theory. Simulation results show the validity and correctness of the control strategy, it is a robust method which can compensate the voltage, current and reactive power simultaneously

This paper is concerned with distribution network reconfiguration in order to maintain load and generation balance at acceptable frequency during the restoration process after a total or partial blackout. The problem is formulated as a constrained multiple-objective optimization problem. AGO algorithm is used to search the proper reconfiguration sequence based on the PN model. The proposed method is designed with consideration to the priority of customers emphatically. At the same time, the restoration is accomplished as soon as possible by minimizing the number of switching operations while the radial network structure is maintained. As a result, a feasible sequence of operations to reach the final configuration is outlined. The effectiveness of the proposed approach has been demonstrated through the test system

The arcing fault has a high probability of occurence on a HV transmission line. To date, the transient resistance is always assumed as a linear constant resistance in most of the locating algorithms. On the basis of the previous achievements in arc modeling, the paper describes an ideal voltage-current transform characteristic relationship and its equivalent circuit representing for long arc, and then presents a novel short time-window method for locating arcing faults on coupled double-circuit HV transmission line using one-terminal voltage and current samples. The method proposed has the advantages as follows: (1) arcing discharge is taken into account; (2) CT saturation is considered for a short time-window, which can be chosen from the initial time of a fault, less than half period; and (3) far-terminal equivalent impedance is not required. Moreover, the requirement of high accuracy to fault location is ensured by using the least error squares method. A lot of digital simulation shows that the scheme is feasible. The method has been applied to Kunming electric network.

Most faults in ungrounded neutral systems are single-phase earthing. Because of the influence of arcing and operating manners, the accuracy of fault line selection algorithms using steady zero sequence current is not satisfactory. In this paper, the effects of arcing on the accuracy of fault line selection are detailed after studying the zero-sequence current during arcing faults. The Clarke transform is employed and the wavelets transform is also adopted to develop a novel method for fault line selection. EMTP is employed to simulating the arcing faults and the simulation is performed under various sampling frequencies and A/D resolution. The results show that the novel method is valid, effective and robust.

The extraction of fuzzy rules is always a bottleneck to fuzzy control systems. This paper proposes a new method to extract the fuzzy rules using rough set theory. The method is applied to obtain fuzzy control rules for substation voltage and reactive power controllers. Even lacking the experience of experts, the fuzzy control rules still could be extracted by the method. By reducing the decision table and calculating the rough subjection degree of every rule, the fuzzy control rules of an on-load tap changer and shunt capacitor with suitable belief degree, are formed. The proposed method not only overcomes the disadvantage of the repeating control in the traditional nine-area control method, but. also avoids the imperfect fuzzy rules extracted by experience of experts directly. As a result, the control rules are objective and the number of regulating on-load tap changers and shunt capacitors is reduced. The test results show that the control effect is satisfied. The proposed method could promote the application of fuzzy control techniques.

In this paper, a new fuzzy neural network (FNN) fault location method based on rough set is presented. The method uses rough sets before the FNN to analyze the indiscernibility relation of data, to remove redundant data and extract the key attribute of electrical components after faults. In order to use the method effectively, a FNN fault location model with a layered and distributed structure system is proposed, which first filters the input data and gets the three-phase power frequency voltage and current, then inputs the voltage and current to a sub-FNN to classify the fault type; finally according to the fault type, it uses a different fault location sub-FNN (including three-phase fault location sub-FNN, two-phase fault location sub-FNN, two-phase grounded fault location sub-FNN and single-phase grounded fault location sub-FNN) to locate faults and output the fault position. Simulations show that the FNN can converge easily and that training time is reduced when using the proposed method.

The study of the digital simulation of electromagnetic transients has been an everlasting issue in power systems. Especially, after improvement by Dommel, the time-domain Bergeron model has been successfully applied in EMTP. But the pre-processing before simulating transients caused by various faults and operations are quite troublesome. This paper presents a new electromagnetic transients simulation method which can be generally used to calculate most of the electric faults in power systems. Unlike EMTP, the presented method doesn't need to calculate the initial values of the system again when the structure or parameter of the system changes. Meanwhile, this method can simulate faults on random locations in single- and double-circuit lines including series compensated lines, bus faults, operation of breakers and open-circuit faults. In addition, the fault-start-angle can be set in the method. Because the new method can conveniently simulate not only inrush currents, overvoltages and harmonics components at different fault locations, but also developing faults, it is significant in line protection simulation verification and overvoltage computation. Lots of tests show that the method is both accurate and fast.