Shu Hongchun

A Novel Control Strategy for UPQC

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

A fault location method of traveling wave for distribution network with only two-phase current transformer using artificial neutral network

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.

A Novel Approach to Distribution Network Reconfiguration Considering the Priority of Customers

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

Analysis on Fault of Yun-Guang hybrid AC/DC Power Transmission System

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.

A novel fault line selection algorithm of single-phase ground faults in ungrounded neutral system using wavelets transform

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.

A novel PI λ D μ controller and its application in UPQC DC voltage control

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 Pi^lambdaD^mu controller are presented in this paper. By using the software MATLAB and EMTDC/PSCAD, the Pi^lambdaD^mu controller and the UPQC are simulated separately. The Pi^lambdaD^mu 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 Pi^lambdaD^mu controller and it is advantaged than the traditional PI control. The Pi^lambdaD^mu controller would be widely used in Power System and other systems.

A least error squares method for locating fault on coupled double-circuit HV transmission line using one terminal data

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.

A new method for locating faults on transmission lines based on rough set and FNN

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.

A new method to detect single-phase fault feeder in distribution network by using S-transform

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 overvoltage research on UHVDC when the UHVDC system runs in single pole way

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.