Table of Content

31 May 2014, Volume 47 Issue 5

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Security Column

Design of Temperature Early-Warning System for High Voltage Cable Connectors

TENG Zhi-jun, HE Xin, LI Guo-qiang, DU Na, GAO Yang

2014, 47(5):  1-5.  DOI: 10.11930/j.issn.1004-9649.2014.5.1.4

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Temperature warning system for high voltage cable connectors plays an important role in protecting the safety of the transmission and distribution line operation. According to the actual layout of the high voltage cable connectors, the physical layer of the early-warning system of ZigBee network is responsible for the acquisition of the temperature of high voltage cable connectors. While the transport layer based on power fibers is in charge of the remote and reliable transmission of temperature data. Thus, a hierarchical-distributed temperature monitoring system for high voltage cable connectors was designed, which adopts ANN to measure the temperature of three-phase high voltage cables at some points, and achieves the temperature warning. The system has high reliability, scalability, and small temperature prediction error, which is suitable for on-line monitoring of the power sector.

Analysis of Lightning Outage for 500 kV Main Transformer

DONG Jia-bin

2014, 47(5):  6-10.  DOI: 10.11930/j.issn.1004-9649.2014.5.6.4

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As for the lightning outage of the phase-B winding of a 500 kV main transformer in a substation of CSG(China Southern Grid), this paper was aimed at finding the reason of the accident. According to the analysis of the test data, there seemed to have a series of fault phenomenon of arc discharges, turn-to-turn short circuit, deformation and even broken-wires in windings. In the disintegration process of the transformer when it was returned to the factory, some factors like free carbon and winding deformation were founded, which verified the initial conclusion from the data analysis. The causes of the accident turned out to be the electromagnetic vibration, which made the paper insulation worn out by the winding block. As a result, the insulation was broken down due to the thunder electric wave invasion, then the inter-tern short circuit fault was induced. In the end of the paper, the anti-accident measures were presented.

Black-Start Plan Assessment for Power Systems with Isolated Island Based on Rough Entropy

OU Wei-jian, FANG Xin-yan, HU Zi-heng, HUANG Mei

2014, 47(5):  11-16.  DOI: 10.11930/j.issn.1004-9649.2014.5.11.5

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Assessment of black-start plans for power system with isolated islands is an issue of fuzzy multi-criteria. An assessment index architecture for black-start plans of power systems with isolated islands was established, in which rough entropy was introduced, the qualitative indices were quantified by using triangular fuzzy number, the continuous attributes were discretized, and the redundant or unimportant attributes were reduced by using rough sets theory. As the result, a method to obtain the weight of assessment indices for black-start plans was conducted, which can be used with the ideal point method to give the sequence of black-start plans for power systems with isolated islands. This method mixes the quantitative and qualitative indexes together reasonably, and takes account of the relevance and redundancy between indexes. A practical example proves its effectiveness and feasibility.

Analysis and Prevention of Seal Welding Cracking in Supercritical Boiler Water Walls

CHEN Ming

2014, 47(5):  17-19.  DOI: 10.11930/j.issn.1004-9649.2014.5.17.2

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It is observed that cracking occurs in the seal welding seams of the 660-MW supercritical boiler water walls in Xuangang Power Plant. The analysis on the cracking from the aspects of materials, welding process, wall plug welding, ambient temperature and welding structure is performed. It concludes that first, the welding performance of 15CrMoR steel is poor and there is a strong tendency to cold cracking; second, as the impurities at the edge of fin cuts, such as iron and oil are not completely cleaned up, the hydrogen content in the welded seams is over high and the defects in the welded seams are much more than the allowable number required by the standard after welding, thus forming the potential cracking; third, the ambient temperature at the construction field is so low that the temperature of the welded pieces drops too fast and the transformation of the deposited metal tissue is incomplete, leading to the formation of hardened tissue; fourthly, the welding stress is large due to the dense distribution of welded seams in the small-diameter and thick-wall tubes, the high tube stiffness and the high space limit. Therefore, appropriate precautions and repairing processes are developedand applied in the construction of the power plant with good results.

ause Analysis on Cracking Tube Leakage of High-Pressure Heater in a Power Plant

SONG Fei, LIU Feng, ZHAO Guang-sen, DENG Yu-qiang, ZHANG Xiang-jin

2014, 47(5):  20-24.  DOI: 10.11930/j.issn.1004-9649.2014.5.20.4

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In a power plant, cracking tube leakage occurs in the high-pressure heaters, which has threatened the operation security of the generating units. In this paper, the causes of the cracking are analyzed by using macro morphology inspection, macro fracture analysis, X-ray energy spectrum analysis of corrosion products and metallographic observation. The analysis results reveal that the radial cracks at the tube orifice are induced by stress corrosion, and the circumferential cracks at the tubes around the tube plate by both corrosion fatigue and stress corrosion, while the main causes of the corrosion are the over-numbered chloride ionsin the water and the air leakage at the drainage side due to the condenser leakage. Some preventive measures are therefore put forward.

Cause Analysis on Steam Turbine Valve Control Misoperation during Grid Instantaneous Faults

ZHANG Bao, YANG Tao, XIANG Jin, FAN Yin-long, GU Zheng-hao, XU Feng, LIU Xiao-sheng

2014, 47(5):  25-28.  DOI: 10.11930/j.issn.1004-9649.2014.5.25.3

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In this paper, several steam turbine fast valve control misoperation events caused by grid instantaneous failures are introduced. In combination with the grid fault record data, several power transmitters of different types are tested. The result shows that when the input signal changes rapidly, distortion happens in the output value of some power transmitters with the distortion direction and amplitude relevant to the phase of faults, fault time, power transmitter connection type and the manufacturer such that the grid fault information may be amplified, which is the root cause of the fast valve control misoperation events. Based on the test results, some suggestions are put forward on the selection and application of power transmitters.

Causes and Treatment of Turbine Oil Deterioration

YAO Ming-zhao

2014, 47(5):  29-31.  DOI: 10.11930/j.issn.1004-9649.2014.5.29.2

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Only after one-year operation severe turbine oil deterioration occurs at two 660-MW units of one power plant showing breen color. The analysis on oil quality and antioxidant is then carried out. It turns out that the diphenylamine antioxidant was added inappropriately to the fresh oil which causes the turbine oil to deteriorate rapidly in high-temperature operation. Based on the analysis result, the oil is treated with oil processing equipment and the T501 antioxidant is added to eliminate the adverse effects of improper antioxidants on oil. Moreover, it is suggested that specifications on oil additives should be put forward to ensure that the oxidation- resistance performance of fresh oils can meet related technical requirements.

Tracing the Source of Black Particles in Fire-Resistant Oil of Unit 2 in a Power Plant

WANG Xiao-wei, ZHAO Ping-zhong, WANG Juan, TANG Jin-wei

2014, 47(5):  32-34.  DOI: 10.11930/j.issn.1004-9649.2014.5.32.2

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Black particles are observed in the fire-resistant oil of Unit 2 in a power plant. Even after the oil treatment with the fire-resistant oil treatment equipments, the black particles still come up occasionally. Through the analysis by SEM, X-Ray energy spectrum and overheat spot searching in turbine regulating system, the black particles are determined to be the coke generated from the fire-resistant oil under the local long-term overheating environment. Therefore, preventive measures are put forward, such as enhancing oil filtering, to remove the carbides and impurity particles from the oil in time, isolating and removing the overheat spots as soon as possible to eradicate the root cause of any potential carbonization from local overheating.

Power System

Detection of Power Quality Disturbances Based on EEMD and Teager Energy Operator

DENG Wei-quan, ZOU Jin-hui, FAN Yu-gang, WU Jian-de

2014, 47(5):  35-38.  DOI: 10.11930/j.issn.1004-9649.2014.5.35.3

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To detect power quality disturbances, empirical mode decomposition(EMD) theory, ensemble empirical mode decomposition (EEMD) algorithm and the Teager energy operator(TEO) are combined to conduct the method, that is based on EEMD and Teager energy operator, to detect power quality disturbances, in which the power system monitoring signal can be decomposed firstly into different single components of intrinsic mode functions (IMF) with different characteristic time scale by using empirical mode decomposition method, and then the instantaneous amplitudes and instantaneous frequencies of the intrinsic mode functions can be obtained by using Teager energy operator, and the amplitude spectrum of the signal can be given. The method takes full advantage of the rapid response capability of adaptive EEMD and Teager operator, and its validity was verified by the simulation results.

Real-Time Risk Assessment Method of Small Signal Stability of Power Systems

SHI Lin, LUO Yi, ZHU Yi-hua, DUAN Tao, LI Xiao-lu, XIONG Wei-bin, LI Mao

2014, 47(5):  39-43.  DOI: 10.11930/j.issn.1004-9649.2014.5.39.4

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In order to get a real-time reflecting of small signal stability of power systems, a set of indices of real-time risk assessment is given, and a real-time risk assessment method of small signal stability of power system is proposed, in which the damping ratio of 0.05 is chosen as the threshold value to judge small signal stability in a modal analysis under current or N-1 status. In addition, the model for real-time failure rates of power transmission lines is used to calculate small signal instability probability under N-1 status. According to the sensitivity analysis of damping ratios, the controlled quantities of the nodes selected by participation factors, are iteratively calculated with the objective of minimizing control cost. The comprehensive and optimized control scheme is generated by coordinating the controlled quantities of all poorly-damped oscillatory modes and the scheme’s cost is taken as the index to evaluate the consequence. Finally, an example based on the data about Central China Power Grid operation and the local weather in a certain time section was taken to prove the effectiveness of the method mentioned above.

Voltage Stability Analysis Based on Thevenin Equivalent Parameters

FU Zheng-xin, LU Ji-ping, QIAO Liang, LI Jun

2014, 47(5):  44-47.  DOI: 10.11930/j.issn.1004-9649.2014.5.44.3

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Through the inverse matrix of the nodes admittance matrix and the off-line solution of power flow, the node’s self-impedance and open-circuit voltage can be gotten respectively, which are the equivalent impedance and source of the two-node network. On the basis of the simplification network, the voltage stability indices were deduced, by which an clear judgment on node voltage stability and its degree can be obtained. In the solving process of the equivalent model of two-node network, the influences of generator’s power resistance and load were taken into account, which made the method simple, widely applied. Furthermore, it can avoid the zero drift in Thevenin solution and larger error when the network has changed.

Power System Simulation in Peer-to-Peer Computing Environment

WANG Shu-zhong, GUO Jian, SONG Dun-wen, SHI Xiu-ping, FAN Ning-ning

2014, 47(5):  48-52.  DOI: 10.11930/j.issn.1004-9649.2014.5.48.4

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In order to solve the computational bottleneck of centralized and large-scale computing systems, improve the response speed and reliability of electric power simulation, and make full use of idle computing resources, a peer-to-peer(P2P) based computing platform for power system simulation was built. The feasibility of the integration of power system simulation with P2P technology was analyzed. By using the hybrid P2P structure, an overall architecture of simulation platform was designed. According to the specific requirements of electric power simulation platform, a P2P communication protocol was stipulated and its syntax and semantics were analyzed in detail. Moreover, a distributed storage system based on P2P structure was studied, which can be applied to the simulation platform with PSD-BPA program. Experimental results show that the platform has a greater superiority in solving large-scale computing problems, and has a broad range of application prospects.

A Distance Protection Scheme of Series Compensated Line Based on R-L Model

ZHENG Tao, GAO Chao, YANG Song-wei

2014, 47(5):  53-58.  DOI: 10.11930/j.issn.1004-9649.2014.5.53.5

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Since the failure characteristics of series compensated lines are more complicated, the distance protection is usually difficult to operate correctly. This paper investigated a new fault location algorithm based on one-terminal signals. This method is conducted by the R-L model of the transmission lines. According to the different fault parameters of the transmission line in front of or behind the series compensation device, two calculation models for distance measurement were presented. By comparing the calculated resistance values with the real values, the relative position of the fault can be located. If a fault takes place in front of the series capacitor, the circuit breaker would be tripped directly. But if the fault takes place behind the series capacitor, the fault location can be found by the presented model and the calculation algorithm mentioned above. This scheme can solve the transient overreach problem in traditional series compensated protection scheme. At the same time, this scheme uses the transient data only before the mental oxide varistor(MOV) conducting, the protection can avoid MOV’s nonlinearity which makes the voltage of series compensated capacitors not easy to obtain. By this method, the reliability of the distance protection can also be improved greatly. At the end, the validity and adaptability of the scheme were verified through the PSCAD simulation.

Study on Regional Protection System of Microgrid Based on Multi-Agent System

ZHAO Feng-xian, SUN Li-ying

2014, 47(5):  59-63.  DOI: 10.11930/j.issn.1004-9649.2014.5.59.4

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With a large amount of distributed generators with various types integrated into the the distribution network, the microgrid is then formulated which has greatly changed the traditional protection configuration of distribution network. Considering its ownstructure of microgrids and the impacts of microgrid on distribution network protection, in this paper, the theory of Multi-Agent system is introduced to the microgrid protection design, in which the microgrid is divided into several subareas, and the faulty region can be locked by obtaining the impedance element and the directional element of power variation within each subarea. Moreover, the distributed processing and cooperation of each Agent is used to implement microgrid protection. Compared with the traditional segment protection, this design is more flexible and reliable in the aspects of relay coordination and overall performance.

Review of New Technologies Impact on Components Reliability Modeling in Power Generation and Transmission Systems

PENG Hui, YANG Fan, ZHAO Shu-qiang, LI Ya-jun, SONG Yun-ting

2014, 47(5):  64-71.  DOI: 10.11930/j.issn.1004-9649.2014.5.64.7

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With the development of power grid construction and the constantly emerging of new power generation and transmission techniques, the new requirements for power system reliability evaluation are put forward in the aspects of accuracy and comprehensiveness. Starting with the reliability modeling of generation and transmission components, the trends of multi-state models with more consideration factors of the generation and transmission components were analyzed. The probabilistic reliability modeling methods for ultra HVDC transmission, VSC-HVDC, wind power plants with energy store devices, FACTS devices and electric vehicles were discussed, as well as their effects on generation and transmission system reliability and the existing shortcomings of the new devices. Finally, the problems to be further researched in future were proposed.

Improving Grid Dynamic Stability by Installing SVCs in Relative Substations in Sichuan-Chongqing Power Grid of UHVAC/UHVDC

CHEN Han-xiong, LI Lan

2014, 47(5):  72-77.  DOI: 10.11930/j.issn.1004-9649.2014.5.72.5

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In order to resolve the problem of insufficient dynamic reactive power support of the load center of Chengdu-Chongqing power grid and improve the grid dynamic stability and transfer spare hydropower from Sichuan to eastern China, the grid dynamic stability by installing SVCs in relative substations in Sichuan-Chongqing Grid of UHVAC/UHVDC was studied based on the planning of the AC-DC Sichuan-Chongqing power grid and the feasibility study of installing SVC at some relative nodes. The results show that the capacity of the AC passage can be increased by about 3 700 MW after installing SVCs with certain capacities on relative UHV notes in Chengdu and Chongqing grids by 2020.

Flexible Insulating Rod for Live Line Working with Ultra-High Voltage

XIANG Wen-xiang, LIU Kai, WU Zheng-rong

2014, 47(5):  78-82.  DOI: 10.11930/j.issn.1004-9649.2014.5.78.4

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Hard insulating rod(“hard rod” for short) for live working with ultra-high voltage of 1 000 kV has the disadvantages of being too long and very heavy, which may cause many troubles in transportation, storage and operation. Therefore, flexible insulating rods were developed through improving the high-performance fibers and the compositively molding of the fiber with thermoplastic material. This new kind of rods can only be of 34.6% weight of hard rod with the same standard. Although the joint of a flexible insulating rod can only be of 10% weight of the steel joint, the specific strength increases to 2.85 times. With resembling in coil shape, the flexible insulating rod overcomes the difficulty of storage and inconvenience during transportation. It replaces hard insulating rod for live line working with ultra-high voltage and boosts the features of being “safe, reliable, light and flexible”.

Calculation Method of Short-Circuit Impulse Current in an Inter-Phase Power Controller

CUI Guang-sheng, SHEN Xu-hui, CHEN Xiang, ZHENG Chao, LEI Zheng

2014, 47(5):  83-87.  DOI: 10.11930/j.issn.1004-9649.2014.5.83.4

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In recent years, intensive grid developments led to short-circuit current overproof increasingly. Therefore, interphase power controllers(IPCs) are receiving attention due to its characteristics of limiting short-circuit current. The system with short-circuit faults, which also contains IPCs, was analyzed by the operation circuit method in this paper, and the detailed expressions of IPC branches’ currents were also conducted. Based on the expressions, the analysis of the influence factors on the short-circuit impulse currents of IPCs as well as the methods of calculation were accomplished. Finally, an equivalent system of 500 kV, containing IPCs, was taken as an example to get the electromagnetic transient simulation results, which prove the feasibility of the proposed method. This research can provide a reference for the selection of interphase power controlles.

Simulation Research on Effects of Distributed Generation on Voltage of Distribution Network

HE Chang-qi, SHAO Long, GAO Yang, LU Jia

2014, 47(5):  88-91.  DOI: 10.11930/j.issn.1004-9649.2014.5.88.3

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Voltage distribution will be effected significantly when distributed power(DG) is connected to a grid. How to reduce the impacts of the distributed power on distribution network voltage has become an urgent problem. By taking IEEE33-node distribution network as an example, a simulation model has been built based on SIMULINK software, with which the impacts on voltage distribution was analyzed when capacity and connected location of the distributed generation were changed. On the basis of a large number of simulation examples and data, a set of practical plans about integration of distributed generation with a grid and guidelines those should be complied with were summarized, by which the security and economy of the distribution networks with distributed generation can be improved.

Generation Technology

Reliability Assessment of DEH System Optimization Based on Dynamic Fault Tree Analysis

QIAN Hong, LUO Jian-bo, JIN Wei-xiao, ZHOU Jin-ming, ZANG Xu-dong

2014, 47(5):  92-96.  DOI: 10.11930/j.issn.1004-9649.2014.5.92.4

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In this paper, an optimization scheme in which power control is switched to main steam pressure control in digital electro-hydraulic (DEH) governing systems is proposed to address the detection system fault issue caused by the power control failure. A dynamic fault tree model is established to assess the reliability of the DEH system functions for the first time. In addition, this dynamic fault tree is also converted into repairable Markov chain to calculate the failure rate. Through the comparison between the failure rates before and after the DEH system optimization, the feasibility of the optimization scheme and its effectiveness on improving the system reliability are demonstrated and verified.

Reformation of Stator Winding and its End Support Structure of TBB-800-2EY3 Turbo-Generator

SUN Shu-wen, WANG Shao-yu, HAN Chang-li, SONG Yu-ke, SHI Xiang-dong

2014, 47(5):  97-101.  DOI: 10.11930/j.issn.1004-9649.2014.5.97.4

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Serious drawbacks exist in the design of stator winding support structure of TBB-800-2EY3 turbo-generator, resulting in several occurrences of faults, such as stator bar insulation wear-out and cooling water leakage during operation. After repaired in its original structure and resumed operation, similar faults occurred in the machine again. In order to eradicate the drawbacks mentioned above, this new techniques of design and manufacture for modern turbo-generators are introduced, which rebuilds the whole stator winding end support structure including stator winding, stator end plates and its screen structure. After the modification, the vibration magnitude of stator end winding, the additional copper loss, the total dc I ² r loss and end plates loss were considerably diminished. The temperature rise of these parts was appreciably reduced also. The operational efficiency and reliability were improved as well.

Comparison Between Single-Shaft and Multi-Shaft of 800-MW Combined Gas-Steam Cycle Units

JING Yong-chang

2014, 47(5):  102-106.  DOI: 10.11930/j.issn.1004-9649.2014.5.102.4

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Multi-shaft and single-shaft configurations require full consideration of the unit performance, capital investment, operation and maintenance cost, operating convenience and the construction space. The analysis and comparison on the two types of configuration are conducted from three aspects, i.e., unit performance, unit configuration and environmental impacts. The unit performance deals with the gross power output, gross efficiency, auxiliary power demand, generator losses and shaft power. The unit configuration involves space limitations and expansion capability. And the environmental impacts include CO₂ and NO_x emissions. The results show that the single-shaft configuration is more suitable for the units with better requirements on unit performance, NO_x emissions, CO₂ emissions, start-up and expansion possibilities, while the multi-shaft configuration is better for the units with limited space but with higher requirement on steam turbine availability and reliability.

R&D of Decision-Making Supporting System for Energy-Saving Thermal Power Generation Dispatching

PENG Zu-hui, SUN Shuan-zhu, DAI Jia-yuan

2014, 47(5):  107-112.  DOI: 10.11930/j.issn.1004-9649.2014.5.107.5

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As the implementation of energy-saving generation dispatching is an important measure to realize energy saving and consumption reduction for China’s power industry, the determination of the sequencing index for thermal generation units is the major component of grid dispatching. Based on the studies of the scheduling rules of energy-saving generation dispatching, and taking the cogeneration units, comprehensive resource utilization power generation units and other conventional coal-fired units as the studying objects, the in-depth study on monitoring indices for all the units is conducted in line with the requirements of online monitoring technologies, and the decision-making supporting system for the energy-saving thermal generation dispatching is developed, which has provided large basic data for making the dispatching plan and theoretical principles for the quantification of unit sequence.

Investigation on the Circulating Water Pump Intake Pit Model Test for Certain Nuclear Power Plant Phase One Project

WANG Bao-tian

2014, 47(5):  113-117.  DOI: 10.11930/j.issn.1004-9649.2014.5.113.4

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As an indispensable precondition, reasonable design of circulating water pump(CWP) intake pit plays a vital role ensuring the secure and economic operation of CWP and circulating water system in nuclear power plants (NPP). According to Froude similarity criteria, a test model with the scale ratio of 1∶30 is designed and used in flow distribution test, free surface vortex test and submerged vortex test for a certain coastal NPP phase one project. The flow distribution countermeasures and anti-vortex device are determined based on the model test results, which is of great practical significance for the project construction such that solid foundations can be laid for the subsequent CWP intake pit design.

New Energy

Design of Coordinated Controller for Micro-grid Based on Multi-Mode Self-adjustment Strategy

HUANG Xiu-qiong, QUAN Wen-lin, LIU Xian-ming, JING Tian-jun, YANG Ren-gang

2014, 47(5):  118-122.  DOI: 10.11930/j.issn.1004-9649.2014.5.118.4

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How to maintain the stability of a micro-grid under different operational conditions is one of the difficulties of micro-grid coordinated control. In the paper, a coordinated control strategy based on multi-state self-adjustment was proposed for hierarchical control scheme of micro-grids. For meeting the construction requirements of the demonstration project, a coordinated controller for micro-grid which has high penetration of wind power and PV was developed. According to the operation status of a micro-grid, the DGs, energy storage and loads can be coordinated to achieve smooth switching under different operation conditions including gird-tied, islanding, standby and shutdown. Finally, simulation software was presented to test the controller. The results verified the practicality of the controller.

Design and Development of Power Prediction Software of Wind / Photovoltaic in a Micro-Grid

FENG Bin, DING Mao-mao, ZHUO Wei-guang, NIU Huan-na, YANG Ren-gang

2014, 47(5):  123-128.  DOI: 10.11930/j.issn.1004-9649.2014.5.123.5

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Micro-grid’s scheduling plan is usually based on the predictable results of the power output of wind turbine generation and photovoltaic generation. This paper used time series model for wind/photovoltaic power prediction, took the concept of equivalent average wind speed to improve the accuracy of wind power prediction, and adopted the way of establishing the model online to correct the model constantly. Finally, the software of weather forecasts was used to correct error to improve the accuracy of the predictable results. The software’s functional composition was also designed. Flowchart of the procedure was also established, which contains ultra-short-term, extension-short-term and short-term predictions. Finally, an example was taken to verify the practicality and effectiveness of the software.

Wind Speed Forecasting Modelling by Combination of Masking Signal Based Empirical Mode Decomposition and GA-BP Neural Network

ZHANG Na, WANG Shou-xiang, WANG Ya-min

2014, 47(5):  129-135.  DOI: 10.11930/j.issn.1004-9649.2014.5.129.6

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For wind power forecasting, the traditional empirical mode decomposition method usually decompose the wind speed signal into several components with different frequencies. However, the mode-mixing phenomenon may exist and affect the accuracy of forecasting. To solve the problem, a new combination model based on the advanced empirical mode decomposition(EMD) and GA-BP neural network was proposed. Firstly, the traditional empirical mode is improved by the masking signal method(MS), by which the original data can be decomposed into more stationary signals with different frequencies. Secondly, each signal is taken as the input data to establish GA-BP neural network forecasting model. Finally, the forecasting results can be obtained by adding up the predicted data of each signal. The proposed method was programmed by C++ and tested by using the data from an actual wind farm. The simulation experiments show that the proposed method can improve the forecasting accuracy and its running time is also short, which is suitable for ultra short term(10 min) and short term (1hour) wind speed forecasting on line. Consequently, it has a certain practical significance.

Design of Coordinated Controller for Micro-grid Based on Multi-Mode Self-adjustment Strategy

HUANG Xiu-qiong, QUAN Wen-lin, LIU Xian-ming, JING Tian-jun, YANG Ren-gang

2014, 47(5):  136-140.  DOI: 10.11930/j.issn.1004-9649.2014.5.136.4

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How to maintain the stability of a micro-grid under different operational conditions is one of the difficulties of micro-grid coordinated control. In the paper, a coordinated control strategy based on multi-state self-adjustment was proposed for hierarchical control scheme of micro-grids. For meeting the construction requirements of the demonstration project, a coordinated controller for micro-grid which has high penetration of wind power and PV was developed. According to the operation status of a micro-grid, the DGs, energy storage and loads can be coordinated to achieve smooth switching under different operation conditions including gird-tied, islanding, standby and shutdown. Finally, simulation software was presented to test the controller. The results verified the practicality of the controller.

Investment Strategies of China’s PV Projects in the Different Tariff Zones

WANG Shu-juan, ZHAO Na, LI Rong-hua, LI Yi-zhen

2014, 47(5):  141-144.  DOI: 10.11930/j.issn.1004-9649.2014.5.141.3

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Because of generation prices of photovoltaic power are in three classes in different areas in China, earnings of stations built in the areas, where may be of rich in solar power, are not always great. By establishing the“resource-electricity output” model and the financial analysis model, this paper set up a direct relationship between the resource and IRR in different tariff zones. The results were analyzed and the following conclusions were obtained: the projects in tariff zone of class Ⅰ will win the best benefits and will be the first choice for investors; apart from a small portion of projects with solar resource in better class, most of the projects in tariff zone of class Ⅲ can obtain a reasonable return on investments only when they gain extra subsidies. The IRR of the projects with the same resources will change by around 0.9% in different tariff zones; the IRR of the projects in the neighboring tariff zones will be the same when the peak hour change about 100~120 h.

Evaluation Index System for Electricity Market Operation Situation Adapted to Green Power Acceptance

FANG Yin, ZHANG Xian, SUN Qiao, CHENG Kai, LU Zheng-lin, YU He, LI Wei-dong

2014, 47(5):  145-149.  DOI: 10.11930/j.issn.1004-9649.2014.5.145.4

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In order to promote the inter-regional exchange of green power, market information should be given briefly and clearly to help the market participants to handle the market dynamics and make reasonable decisions. According to the constructing principles of an index system, and combining the concept of market adequacy and its model, an index system for the evaluation of electricity market operation situation was constructed, which will adapt to green power acceptance. It includes three-level evaluation indices displaying the whole market situation, market adequacy, constraints among the generation, transmission and load, and the trend and risk of the market, by which the electricity market operation can be shown clearly and roundly, and the very useful market information can be provided to market participants.

Information and Communication

Design and Realization of the Linux-Based Consolidated Monitoring Unit Prototype in Substations

ZHANG Fan, ZHU Yong-li, XIONG Hai-jun, WANG De-wen

2014, 47(5):  150-154.  DOI: 10.11930/j.issn.1004-9649.2014.5.150.4

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Consolidated monitoring unit is the key element in implementing the unified communication platform of on-line monitoring system for substation. To solve the problem that some unstandardized devices cannot communicate with the monitoring systems in conformity with standard of IEC 61850, a prototype of a consolidated monitoring unit was developed on the Linux-based embedded platform, which can complete the protocol conversion from MODBUS, IEC60870-5 and proprietary protocols to IEC61850. For implementing the access of the monitoring devices by MODBUS protocol, the database and software architecture design of the consolidated monitoring unit were given. And the functions were tested by the standardized information models and the real monitoring devices, by which the reliability and functional integrity of the prototype were verified.

Communication Implementation of GPRS Based Fault Location System in Power Distribution Networks

WU Zhen-hua, LANG Bing, XIN Li-ling

2014, 47(5):  155-159.  DOI: 10.11930/j.issn.1004-9649.2014.5.155.4

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In a GRPS-based fault location system (GRPS: general packet radio service), if a DTU (data transfer unit), which has already built the communication with its data centre, doesn’t send data to the data centre for a long time, the built communication will emerge off-line phenomenon. Generally, the heart-beat packet method is used to reduce the frequency of off-line phenomenon and enhance its ability of on-line communication. But, some types of DTUs don’t have the heart-beat packet function. To solve the problem, an intermittent communication method was proposed,which is reverse to the method based on “heart-beat” package and works by asking the DTUs to keep in touch from the data center, thus making the off-line problem solved. Moreover, the intermittent communication method was integrated into the fault analysis software(FAS) of the data center through programming, which make the FAS has the ability to enhance on-line communication ability of DTU. Finally, the experiment data and analysis verified the effectiveness of the proposed method.