ISSN 1000-1026
CN 32-1180/TP
  • ISSN 1000-1026
  • CN 32-1180/TP

Volume 31,Issue 22,2007 Table of Contents

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Operation reliability and wide area security defense
Adaptive Optimal Restoration Control for Interconnected Grids
WANG Haohao1,2 , XUE Yusheng2,1 , Zhaoyang DONG3 , Gerard LEDWICH4 , LIU Yutian5
2007, 31(22): 1-5.
[Abstract](1444)[HTML](0)[PDF ](807)
The model of optimal restoration control considering the income from restored loads and control cost, as well as the control risk is presented. A two-layer framework for optimizing is proposed, which uses a procedure of“parallel optimization for subareas and dynamic coordination among subareas”, to overcome the drawback of offline made restoration schemes based on fixed scenarios and fixed priority for countermeasures. Moreover, restoration strategy is extended from bottom-up one, which is widely discussed nowadays, to top-down one as well as hybrid one. Studies include the inner optimization of each strategy and coordination between different strategies. Based on a viewpoint of adaptive optimization and risk decision-making, related modules and algorithms are designed. A framework of the online decision support system is presented, the three parts of which are information collecting, analysis and control. The validity and adaptiveness of the decision support system are verified by simulations.
Study and Implementation of a Software Development Pattern for Online Transient Security Early Warning and Protecting System
ZHAO Chuanlin, WU Wenchuan, ZHANG Boming, SUN Hongbin
2007, 31(22): 6-10.
[Abstract](1304)[HTML](0)[PDF ](762)
To make the online transient early warning and security protecting system easy to reuse and maintain, a software development pattern is proposed. Several advanced methods, such as architecture analysis, design pattern, framework and unit testing, are used in this pattern to enhance the development efficiency and software quality. A layered architecture is introduced during the design process and a“strategy pattern” is used to adapt to the changing requirement for the dynamic model of the component concerned. An open framework for distributed task dispatching is also presented. A“subscriber/publisher” pattern is used to implement message exchange between the server and clients, which is adaptive to the hardware configuration changes. An online transient early warning and security protecting system based on the methods proposed has been developed and put into actual operation in a provincial power system.
Generation Reliability Exponential Analytic Model of Interconnected Areas and Its Application Part One Theoretical Methodology
SUN Rongfu, CHENG Lin, SUN Yuanzhang
2007, 31(22): 11-15.
[Abstract](1219)[HTML](0)[PDF ](751)
Generation system reliability of a single area will be improved by the supports from other areas' generation capacity through interconnection, however the current generation reliability calculation algorithms cannot take this into account due to the computation burden. An exponential analytic model is proposed in this paper based on the generation system reliability of interconnected areas. The effects of installed capacity of each area and of transfer capability of tie lines on the generation system reliability in each single area are modelled by establishing the matrices of influence distribution indices. The generation reliability is calculated as an exponential function of regional reserve capacity and tie lines transfer capability, which can effectively consider the interaction between different areas. Test results on a simple two-area system and the TH-RTS indicate that the precision and effectiveness of the model.
Computing Delay Margin of PSS with Commensurate Communication Delay Considering Wide-area Damping Control
LIU Meizhao, XIN Huanhai, GAN Deqiang
2007, 31(22): 16-20.
[Abstract](1209)[HTML](0)[PDF ](690)
The aim of this paper is to provide a quantitative stability analysis of a time-delay power system stabilizer(PSS) system with centralized wide-area control using additional global signals. Frequency-sweeping(FS) test is proposed to compute the delay margin of two-level PSS design and the system with additional inter-area damping, and the control performance is further estimated quantitatively. Simulation results verify the validity and pragmatism of the proposed method.
Modeling of Long-term Dynamics for Interconnected Power Systems with Structure-preserved Network
YI Haiqiong1 , DU Zhaobin2 , CHENG Shijie1 , ZHANG Yao3 , HOU Yunhe4 , SHI Libao4 , NI Yixin2
2007, 31(22): 21-26.
[Abstract](1049)[HTML](0)[PDF ](1004)
In order to study the long-term frequency and voltage dynamics of interconnected power systems under cascading events, this paper suggests an appropriate mathematical model and its simulation algorithm with the network structure preserved. Similar to traditional dynamic power flow, the proposed model assumes that the system has survived the transient stability and has sufficient damping torque. Therefore, the relative swings among generator rotors in one area will be neglected in long-term dynamics; and each control area is recommended to have a uniform frequency, represented by its area center of inertia(COI), with a simulation of the long-term frequency and voltage dynamics and the investigation on its effective control strategies. Computer test results of the IEEE 3-area 30-bus system show the validity and effectiveness of the proposed model and algorithm. The proposed simulation tool can be used to study long-term frequency and voltage stability control of interconnected power systems.
Basic Research
Mechanism Analysis of Increasing Amplitude Low Frequency Oscillation Based on Modal Series with Third-order Analytical Solution
DENG Jixiang1 , CHEN Wuhui2 , HE Jianming1
2007, 31(22): 27-30.
[Abstract](1191)[HTML](0)[PDF ](761)
The third-order analytical solution of dynamic power system is used to investigate the complex nonlinear dynamical behavior of power systems after the occurrence of large disturbances. A new point of view is presented firstly to theoretically explain the reason of the increasing amplitude inertia mode oscillations after occurring large disturbances, that the higher order terms in the third-order analytical solutions are exited by the large disturbance and the nonlinear interaction among the modes is intensified. The analysis result for a power system case shows that the new finding is correct and the third-order analytical solution is more effective in analyzing the complex dynamical behavior of power systems after occurring large disturbances than the second-order analytical solution.
Security Forewarning Method of Maximum Load Capacity Based on Fuzzy Clustering
ZHANG Jing, YANG Minghao
2007, 31(22): 31-35.
[Abstract](1274)[HTML](0)[PDF ](984)
To meet the demand of static security analysis of power system, a forewarning method is proposed based on the voltage stability index related to the maximum nodal load capacity. The method uses red, yellow and green colors to label a power system capacity and boundaries to withstand load increasing at a single node. The voltage stability indices indicating the maximum nodal load capacity are defined as feature vectors. According to the real time feature vectors, nodes are classified into different sets with fuzzy clustering method and colored according to the logical rules. The permitted load increasing ranges can be obtained in off-line simulations. Simulations on an IEEE 30-bus system illustrate the effectiveness of the method.
Analysis on Mal-operation of Differential Protection Caused by Sympathetic Inrush
BI Daqiang1 , SUN Ye1 , LI Dejia2 , YU Gaowang3 , WANG Xiangheng1 , WANG Weijian1
2007, 31(22): 36-40.
[Abstract](1359)[HTML](0)[PDF ](996)
It is increasingly known that the sympathetic inrush may cause the mal-operation of differential protection for transformer or generator, and affects their normal running. Up to now, because the effective measure is no available to identify the sympathetic inrush, the second harmonic restraint scheme against initial inrush and third harmonic based current transformer(TA) saturation criterion are used to prevent differential protection to mal-operation caused by the sympathetic inrush. Considering the characteristics of sympathetic inrush, it is analyzed that mal-operation of differential protection related to sympathetic inrush is mainly due to the TA saturation. Further, through the mal-operation cases in practice and simulation results, the effectiveness of TA saturation criterion is analyzed under different connections between transformers, such as in parallel, in series and their coexisting. The analysis results verify that the TA saturation criterion can play a certain role in blocking the differential protection for transformer connection in series, but it may be invalid under transformer connection in parallel or parallel and series coexisting.
A Novel Principle of Phase Selection for Transmission Line Protective Relaying Based on Time-domain Correlation Analysis
SUONAN Jiale, DENG Xuyang, GAO Feng, GU Jia, XUE Xiaohui
2007, 31(22): 41-45.
[Abstract](1248)[HTML](0)[PDF ](785)
On the basis of the boundary conditions of different types of fault, this paper analyzes the current fault component of different phases. A novel principle of phase selection based on time-domain correlation analysis is proposed. This principle is not only suitable for the non-periodic component, fundamental component and harmonic component, but also correct in the transient process of the fault. Furthermore, this principle is insensitive to transition resistance and fault location. It can select the fault phase quickly and correctly. In particular, the three-phase fault can be identified correctly. ATP simulation results and physical dynamic data testing results have both verified the effectiveness of this principle.
Distribution Network Reliability Considering Distribution Generation
LIU Chuanquan, ZHANG Yan
2007, 31(22): 46-49.
[Abstract](1733)[HTML](0)[PDF ](981)
Island is a new operating mode when the distribution network is incorporated with distributed generations. Based on the importance of the load an optimization model of distribution network islanding scheme is established, in which the maximum equivalent load is taken as objective function. A solution based on depth-first search and breadth-first search technology is given. By considering the islanding operating mode, the paper improves the minimal path method of the traditional reliability calculation and makes it suit to calculate the distribution network with distributed generation. The simulation of IEEE-RBTS Bus 6 system demonstrates the efficiency and practicability of the mode. The calculating results indicate that the distributed generation connected to distribution network can improve the reliability of the distributed system.
Dead-beat Control Strategies for Fault Ride-through Capability Enhancement of Variable Speed Asynchronous Machine Wind Energy Conversion Systems
Maliki GUINDO, WANG Chengshan
2007, 31(22): 50-55.
[Abstract](1068)[HTML](0)[PDF ](738)
Variable speed wind turbines are very sensitive to any disturbance, faults and grid voltage sags. They are disconnected from the grid whenever these conditions arise and reconnected once the grid is healthy. Maintaining the wind turbine connected to grid during disturbances is a real challenge. Future grid codes will require wind turbines(WTs) to be connected to the host grid even during the fault condition and to have voltage sag ride-through(VSRT) feature installed. VSRT feature is not available in most of the present WT and few do with hardware modification, thus increasing the cost of the system. In this paper, a control strategy and VSRT for WTs equipped with full-load converter connected asynchronous generators is presented to maintain the turbine connected to grid during fault and post fault condition without hardware modification. The controller of the electric subsystem of the WT is designed following the strategy of“predictive” deadbeat control. The transient behavior of a 300 kW WT during and after a 30% voltage sag, at which WTs are normally programmed to trip, has been simulated and the fault ride-through performances of the controller demonstrated.
Application Research
Control Structure of a Real-time Agent with Equal Negotiation Mode and Its Application
TONG Xiaoyang, WANG Xiaoru, TAN Yongdong
2007, 31(22): 56-60.
[Abstract](1423)[HTML](0)[PDF ](710)
A general control architecture of a real-time agent is presented for a distributed real-time multi-agent system from the point of view of design and implementation. Some mechanisms in the control architecture are studied, such as the perception of the environment, coordination and negotiation with messages, high-level perception based on wide-area information, integrated decision-making and scheduling. When the control architecture is applied to the design of a wide-area backup protection system, the working processes of some main modules in the protection agent are given. Some key implementing methods in designing the protection device are expatiated. The design scheme for the protection agent is intended to serve as a reference for future development of wide-area protection devices.
A Verification and Control Method for the Consistency of IEC 61850 Information Model
ZHAO Youcheng1 , ZHAO Manyong1 , ZHANG Jie2
2007, 31(22): 61-64.
[Abstract](1208)[HTML](0)[PDF ](912)
In order to meet the needs of the fault management information system and to improve the inconsistent status among the information items and semantic content for the intelligent electronic devices(IEDs), with the IEC 61850 information model as the management object, a verification and control method for the consistency of the IED information models is proposed by using the information semantic theory and object-oriented theory. The method proposed can change the management of the semantic dictionary from the static state to object-oriented dynamic management, thus achieving consistency of the information semantic content for the secondary system and control over its development process.
Data Compression Method Based on Lifting Wavelet Transform and Hybrid Entropy Coding
ZHOU Rui, BAO Wen, YU Xiao, HE Huixin, LIU Jinfu
2007, 31(22): 65-69.
[Abstract](1305)[HTML](0)[PDF ](806)
For the urgent demand of real-time data compression of large turbine-generator units online monitoring and remote diagnosis, a novel real-time data compression and reconstruction method combining lifting wavelet transform and hybrid entropy coding is proposed. The signal to be compressed is firstly decomposed with biorthogonali filters based on lifting wavelet transform and the hard-threshold method is then applied to the wavelet coefficients. In order to implement higher efficient compression, a hybrid entropy coding scheme is employed to code the reserved coefficients. This method has been applied to the real-time data acquired from a large turbine-generator unit. Simulation results indicate that the proposed scheme which combines both lossy and lossless compression techniques can achieve satisfactory compression performance in applications.
An Algorithm for Frequency Measurement Based on DFT
ZHANG Tongzun, SHAO Junsong, FANG Yongjie
2007, 31(22): 70-72.
[Abstract](1200)[HTML](0)[PDF ](1005)
An algorithm for frequency measurement based on discrete Fourier transform(DFT) is analyzed, in which the difference between frequency deviations of two adjacent cycles of the signal is not considered. So the frequency measurement error is rather big when the signal frequency variation is rapid. To solve this problem, an improved algorithm is proposed, in which the influence of difference between frequency deviations of two adjacent cycles of the signal on frequency deviation measurement is considered using the original method. The improved algorithm takes the rate of frequency variation of the signal as a parameter and two methods to identify the parameter are given. One consists in using the rate of frequency variation obtained in the preceding calculation, and the other in using the relatively fixed rate of frequency variation. The results of numerical simulation show that the improved algorithm can give fairly good frequency and accuracy in measuring the rate of frequency variation.
Study on Convergence of Adaptive Filtering Measurement for Power Signal
LI Huiyu1,2 , YU Shenglin1 , JI Kan2 , LUO Xiaoli2
2007, 31(22): 73-76.
[Abstract](1178)[HTML](0)[PDF ](698)
Based on the nonlinear system theory, the stability and convergence of adaptive filtering measurement for power signals are analyzed and demonstrated to find its convergent condition and to design an appropriate adaptive filtering measurement method. Traditional steady measurement is an open-loop method and may misjudge in case of asynchronous sample and signal disturbances. The adaptive filtering measurement method is a close-loop method and it can be employed to deal with non-sin and non-period data, caused by asynchronous sample and non-integer harmonics, and to estimate and correct distortion. The adaptive filtering measurement method can be applied in accurate and reliable measurement in the steady power system.
A Filtering Algorithm for Eliminating Effect of Transient Component and Its Application on Fault Location
LIANG Yuansheng, WANG Gang, LI Haifeng
2007, 31(22): 77-82.
[Abstract](1114)[HTML](0)[PDF ](819)
During the fault transient process, the accurate extraction of power-frequency components is affected by the decaying dc and other transient components existing in the transient voltage and current signals. This paper proposes a novel filtering algorithm to extract the accurate fundamental and integer harmonic frequency component by means of a set of linear equations, which is transformed from a non-linear equation representing the error in discrete Fourier transform affected by decaying dc. Meanwhile, by analyzing the discrete integral error, a correctional scheme is proposed. Extractions from several typical signals and analysis of the frequency response characteristics prove that the proposed algorithm is accurate and stable and has the anti-interference ability for non-integer harmonic frequency component. Extensive tests of fault location show that the algorithm can efficiently improve the precision of fault location during the transient process.
Fault Location Algorithm Based on Wavelet Transform and Neural Network in Distribution Network
ZHANG Fan1 , PAN Zhencun1 , MA Shanshan1 , MA Linlin1 ,WANG Hongwei2
2007, 31(22): 83-87.
[Abstract](1251)[HTML](0)[PDF ](853)
Up to now, the problem of single-phase-to-ground fault location has still not been satisfactorily solved. In analyzing the laws governing the zero mode and aerial mode traveling wave transmission, the authors have found the relationship between the transmission time gap of the zero-aerial mode traveling wave and fault distance, and the law of variation of Lipschitz index of the zero mode wave head with fault distance. Based on the aforementioned analysis, a wavelet transform and BP neutral network based fault location algorithm is presented, which takes the advantage of the time-frequency analyzing capacity of wavelet and the robust nonlinear fitting capacity of neural network. The effectiveness of the criterion has been verified by the ATP simulation results, indicating that the algorithm proposed is immune to such factors as branch lines, primary phase angle of fault and transitional resistance.
Improvement on Loss-of-excitation Protection of Synchronous Generators
LIN Li1 , MOU Daohuai1 , SUN Caixin1 , MA Chao2 , CHENG Tao3
2007, 31(22): 88-93.
[Abstract](1267)[HTML](0)[PDF ](901)
The loss-of-excitation protection of synchronous generators is one of important protections in the power system relay protection. The excitation protection is a complex problem because the excitation faults are related to the large-disturbance stability of generators. The operational situation of the current excitation protection hasn't been ideal and so needs further study on. The shortage of three excitation protection criterions applied currently is analyzed, which based on small-disturbance stability analysis principle without considering the changes of dynamic power-angle character of the generator, or without considering a rather large common area between measuring impedance circle after complete loss-of-excitation and measuring impedance circle after a disturbance at normal excitation operation. So the maloperation or misoperation is difficultly avoided. Based on the simulation analysis of dynamic varying process of synchronous generators after losing excitation, an improved scheme based on direct power-angle measurement is put forward, including setting conditions and calculation method of loss-of-excitation protection of synchronous generators. Simulation results show that the presented protection scheme can judge excitation fault reliably and rapidly, and at the same time, its operation is stable with flexible and easy setting mode.
A Novel Characteristic of Rotor Bar Breaking Fault in Induction Motors
SUN Liling1 , XU Boqiang1 , SUN Junzhong2
2007, 31(22): 94-98.
[Abstract](1062)[HTML](0)[PDF ](741)
According to the basic characteristic of rotor bar breaking fault in induction motors and the physical concept of Hilbert transform of sinusoidal signal, this paper presents the definition of Hilbert modulus of the filtered stator current signal of induction motors. Corresponding algorithm is given by integrating techniques of Hilbert transform, spectrum analysis/correction and self-adaptive filter perfectly. The paper reveals the rule that the area in complex plane occupied by Hilbert modulus of the filtered stator current signal can reflect whether rotor bar breaking fault occurs or not. It shows that the value of Hilbert modulus will increase with the development of this type of fault in induction motors. Results of thorough investigation based on a variety of simulation and experiment demonstrate that the revealed rule is correct. Moreover, a novel characteristic of rotor bar breaking fault is proposed, i.e. the Hilbert modulus gyration radius of the filtered stator current signal. Simulation and experiment results show that the Hilbert modulus gyration radius of the filtered stator current signal, as a characteristic of rotor bar breaking fault, is sensitive to the fault itself and robust to some extent to the load. Hence it can be used to detect rotor bar breaking fault in induction motors.
Egineering Application
Discussion on Application of Disturbance Control Standard in East China Power Grid
GAO Fuying1 , GAO Xiang1,2 , JIA Yanbing3 , YAN Zheng3
2007, 31(22): 99-103.
[Abstract](1231)[HTML](0)[PDF ](697)
The disturbance control standard(DCS) commended by North American Electric Reliability Council(NERC) is briefly introduced. By analyzing the technical characteristics of DCS, the relationship between DCS and area control error(ACE), system frequency and control performance standard is described. To combine the disturbance accident happened in East China power grid(ECPG), it is pointed out that the ability of accident reserve of control areas in ECPG can be effectively reflected. Aimed at the characteristic of energy management system(EMS) in ECPG, the feasibility to implement the DCS in ECPG is put forward to provide technical evaluation means for reasonably deploying the reserve capability and save the system resources. By combining the monitoring demand of DCS, the adjusting guidance for the automatic generation control(AGC) system in the control areas of ECPG is proposed.
Simulation Analysis on Application of Controllable Reactors in 750 kV Northwest China Power Grid
PAN Xiong, DING Xinliang, HUANG Mingliang, YANG Panfeng
2007, 31(22): 104-107.
[Abstract](1300)[HTML](0)[PDF ](950)
Hami-Yongdeng transmission corridor connects the Northwest China power gird and Xinjiang power grid. It is proposed to allocate 750 kV controllable reactor on that line to improve the regulating and controlling capability to power flow and restrain the power-frequency overvoltage and secondary arc current. Base on the 750 kV transmission systems operating modes of Northwest China power gird in 2010 and 2020, the influences of high voltage controllable reactor on long term economic operation and dynamic performance of power system are analyzed. The economic benefit from the application of high voltage controllable reactor is also evaluated. Results show that its application helps to optimize power system steady state operation and improve its electro-mechanical and electro-magnetic performance. It is concluded that considering the economy, security and flexibility of power dispatch, it is preferable to allocate high voltage controllable reactor at Zhangye substation.
Implementation Scheme of Voltage-current Mode for Quasi-real-time Feeder Automation
YANG Hui1,2 , WU Fubao3 , L Hongbing1 , JIN Youhong2
2007, 31(22): 108-111.
[Abstract](1087)[HTML](0)[PDF ](856)
Through analyzing difficulties in implementing the overhead line feeder automation, an implementation scheme for the quasi-real-time line feeder automation of voltage-current mode is presented from the viewpoint of practicality. The scheme can identify feeder fault by detecting the fault current and thus avoid unreliability rendered by the time delay matching and residual voltage when locating the fault by use of voltage signal. Taking advantage of the alternate current operation mechanism, the scheme improves the running and operating reliability of outdoor switches. Moreover, the scheme reaches the flexible construction of the communication network for distribution network based on the GPRS/CDMA wireless communication as well as the quasi-real-time information transmission for the fault signal.
Experience from worksite
2007, 31(22): 112-115.
[Abstract](1057)[HTML](0)[PDF ](627)

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CN 32-1180/TP

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