Showing papers in "Power system technology in 2006"

Optimal Design of Power System Stabilizer Using Particle Swarm Optimization

Abstract: The performance of traditional power system stabilizer (PSS) is evidently influenced by its parameters. To enhance the damping of power system electromechanical transient model, a new method to optimize the parameters of PSS is proposed. Based on two eigenvalue-based objective functions, the parameters of PSS are optimized by use of improved particle swarm optimization (PSO). The results of both eigenvalue analysis and nonlinear simulation show that the PSS with optimized parameters can effectively damp local and interarea oscillations and enhance the robustness of power system.

A Preliminary Exploration for Design of ±800kV UHVDC Project with Transmission Capacity of 6400MW

Abstract: Some technical problems concerned in system design and engineering design of UHVDC transmission project are comprehensively researched.The feasibility of applying UHVDC to outward transmission project for electricity generated in Jinshajiang hydropower station is adequately expounded and proved.According to the experiences of conventional HVDC transmission projects and centering on the technical features of UHVDC transmission,several novel design approaches and viewpoints are proposed.

Fundamental Theory of Forced Power Oscillation in Power System

Abstract: The fundamental theory of forced power oscillation in power system is explained by a single-machine infinite-bus power system model. The main factors related to the forced power oscillation are analyzed, and the forced power oscillation in the single-machine infinite-bus power system is verified by digital simulation. The theory of forced power oscillation in power system proves that the forced power oscillation may be caused by a sustained cyclic small disturbance in power system, and the resonance could be induced if the frequency of the sustained cyclic small disturbance is close to an inherent oscillation frequency, so that it leads to forced power oscillation with high amplitude. The amplitude of forced power oscillation induced by resonance is related with the amplitude of disturbance and the damping of the inherent oscillation mode. The higher the amplitude of disturbance is, the larger the amplitude of resonance is; the stronger the damping of the inherent oscillation mode is, the smaller the amplitude of resonance is. The behavior of forced power oscillation induced by resonance is similar to that of low frequency power oscillation induced by negative damping which is one of free oscillations, but the causes of these two types of power oscillations are different.

Improvement of Power Quality and Stability of Wind Farms Connected to Power Grid by Battery Energy Storage System

Abstract: The authors research the possibility of employing battery energy storage system(BESS)for providing auxiliary service to enhance the performance and controllability of a large wind farm.A mathematic model of battery energy storage system(BESS)based on equivalent circuit and an asynchronous generator based global dynamic mathematical model for wind power generation system are built,and corresponding control strategy is developed.Based on these models,a simulation platform of BESS and wind farm is developed by using Simulink of the Matlab.Taking the wind speed changed at random and serious disturbance in power grid for example,using the detailed wind turbine model and squirrel-cage asynchronous generators the simulation of improving power quality and stability of wind farm connected to power grid by BESS is performed.Simulation results show that the power quality and stability of wind farm connected to power grid can be well improved by battery energy storage.

Islanding Algorithm of Distribution Networks with Distributed Generators

Abstract: The island is an important operation mode of the distribution system with distributed generators to improve power supply reliability of distribution network. To immediately draft an optimized islanding scheme while the fault occurs in distribution network, an islanding algorithm is proposed, in which the simplified model of distribution network is used and according to the requirement of power balance under island operation and different requirements of various consumers to power supply reliabilty, the heuristic search strategy is adopted, so that feasible islanding scheme can be obtained in a short time period. Here, two typical islanding cases are given. The results from the case study and theoretical anlysis show that with the proposed algorithm an optimized islanding scheme can be dynamically generated according to the prefault practical operation situation after the fault occurred in distribution network.

Main Features and Key Technologies of Digital Substation

Abstract: The construction of digital substations is the foundation of digital power grids. In view of technical basis of digital substation at present, the authors analyze main technical features reflecting the property of digital substation and point out that the non-conventional instrument transformer, the reliability of network communication, IED interoperability, time synchronization and information security are key technologies to implement digital substation. Finally the technical and economical significance of these new technologies are summarized.

Present Situation and Prospects of Applying Composite Insulators to UHF Transmission Lines in China

Abstract: The course of developing composite insulators and its large scale application in China are reviewed,and the statistics of domestic operating experience of composite insulators is given.The main failures which appear during the application of composite insulators,such as brittle fracture of rods,mechanical property,interface breakdown,creepage flashover,ageing performance and so on,are summarized and analyzed.The prospects of applying composite insulators in UHV transmission lines are forecasted.

A Survey on Demonstration of UHV Power Transmission by State Grid Corporation of China in the Year of 2005

Abstract: At the end of 2004, State Grid Corporation of China (SGCC) put forward the strategic objective of developing UHV power transmission. Here, the demonstration process of developing UHV power transmission in China by SGCC since 2005 and the significance and necessity of carrying out such demonstration, the selection of demonstration project for UHV AC power transmission and the demonstration process of UHV DC power transmission from Xiluodu and Xiangjiaba hydropower stations in Jinsha River valley, as well as the. research results on the key technologies of UHV power transmission, for instance the selection of voltage class for UHV power transmission, environment protection, AC over-voltage, etc., are presented. Above-mentioned substances show that the research and demonstration processes are scientific and democratic, the results of research and demonstration are reasonable and reliable, and these results can give strong and vigorous supports for the construction of domestic UHV power transmission.

A Wide Area Protective Relaying System Based on Current Differential Protection Principle

Abstract: A wide area protective relaying system based on the principle of current differential protection is presented, the operation mode of this system is described, and the principle to partition wide area protective region and the method to search the protective intelligent electronic device (IED) which is necessary in the implementation of wide area differential algorithm are researched. Taking a power system with double busbar scheme for example, the procedures of searching the associated area of protective IED are illustrated. To ensure the rapid and reliable transmission of sampled value of current in wide area protection system, the IEC 61850 based transmission model for sampled value of current and the general principle of mapping this model to Ethernet communication stack are introduced.

Present Situation and Prospect of Research on Flashover Characteristics of Polluted Insulators

Abstract: The research status on flashover characteristics of polluted insulators in recent decades, including methods to token the operation condition of polluted insulators, correlation among flashover voltage, pollution level and air pressure, and problems to be clarified are summarized Meanwhile the prospect on the research of pollution characteristics of insulators in the future is described and the major research contents from now on, such as the artificial testing method of polluted insulators, the flashover characteristics of long string of insulators under the complicated conditions of low air pressure, ice or snow coating, acid rain or fog and the revision on pollution level, are pointed out

Analysis on Technical Line Losses of Power Grids and Countermeasures to Reduce Line Losses

Abstract: According to measured results of loads in power grids, the distribution and composition of technical line losses of power grids are analyzed by theoretical calculation of line losses Based on the theoretical calculation results of line losses by State Grid Corporation of China in the year of 2005, the main problems of technical line losses of power grids in China are analyzed and corresponding countermeasures to reduce technical line losses are proposed

A Survey on Power System Wide-Area Protection and Control

Abstract: The challenges and opportunities, which power grids are confronted with at present, are analyzed. The development of the functions, control strategies and related technologies of wide-area protection system at home and abroad is presented. The difficulties that current research on wide-area protection is faced with are expounded. The authors point out the development trends of wide-area protection system in the future, they are: being integrated with traditional protections and SCADA/EMS, adopting multi-agent architecture and establishing new mechanisms for information exchange and pre-warning.

A Practical Method of Parameter Aggregation for Power System Dynamic Equivalence

Abstract: To reduce the calculation amount of numerical simulation in transient stability analysis for large-scale power grid, the grid can be simplified by dynamic equivalence The dynamic equivalence of power grid includes three parts: (A) dynamic recognition of coherent unit groups; (B) network simplification and (C) parameter aggregation of coherent unit groups In part (C), a weighing method based approach for parameter aggregation of detailed model of coherent unit groups is proposed, by which the detailed model parameters of equivalent generating set and it regulating system as well as that of equivalent asynchronous motor of load can be obtained Using the proposed approach, not only the purpose of parameter aggregation can be realized, but also the calculation time is reduced The results from ETMSP/MATLAB based simulation of IEEE 10 machine 39-bus system show that the proposed approach is feasible and available In addition, taking a simple distribution system for example, the effectiveness of the proposed approach to the equivalence of asynchronous motor groups is also verified

Impacts of Distributed Generation on Steady State Voltage Stability of Distribution System

Abstract: The authors present a commonly used index used in the analysis of static voltage stability of distribution networks.By means of case calculation the impact of various kinds of DGs and their different installation positions in distribution network on static voltage stability of distribution system is analyzed.The applied static voltage stability index is researched and the relation between this index and load scale factor(LSF)is obtained.The conclusions obtained from the test system may be available for distributed generation planning in distribution networks.

Risk Assessment of Power System Cascading Failure Considering Hidden Failures of Protective Relayings

Abstract: Cascading failure is one of the main causes of blackout. The authors propose an integrated approach to assess the risk of power system cascading failure considering hidden failures in protection system. Two probability models of protection system hidden failures are used to demonstrate their effects on power system risk. The mechanism and scheme of protection system have been analyzed for their contribution to cascading failures after fault occurs. The risk of power system cascading failure is assessed by bus isolated risk, load isolated risk, grid break-up risk and integrated system risk, on this basis the preventive measures to reduce the risk of power system cascading failure is put forward. By means of Monte Carlo simulation approach the stochastic properties of contingencies, protective devices and protection system hidden failures are procreated, and the software for prevention and assessment of the risk of power system cascading failure is developed. The results of applying the proposed method to IEEE 118-bus test system illustrate the feasibility of this method and effectiveness of the developed software.

Impact Analysis of Hourly Weather Factors in Short-Term Load Forecasting and Its Processing Strategy

Abstract: Short-term load forecasting is of great significance to secure and economic operation of power grids, so that novel load forecasting models are always studied to improve forecasting accuracy. Because the portion of the load sensitive to meteorology in the total load becomes more and more great, the key problem in the endeavor of improving the load forecasting accuracy is how to consider the influence of meteorological factors on power loads more reasonably. For a long time past due to that the weather service cannot provide real-time weather forecasting results such as temperature, etc., the overwhelming majority in load forecasting models are established on the basis of daily characteristic meteorological factors, e.g., daily maximum temperature, daily minimum temperature and so on. For short-term load forecasting, after examining the action of meteorological factors and analyzing the strategies to process meteorological factors in different stage, the authors propose a new artificial neural network (ANN) based short-term load forecasting model considering hourly weather factors and strive to find out the correlativity and varying pattern of load curve with real-time meteorological factors such as temperature, relative humidity and other weather variables. Actual applications show that by use of the given forecasting model and processing strategy the obtained forecasting results are more accurate, in addition, the proposed forecasting model is also applicable to ultra-short term load forecasting.

A Survey on Detection Algorithm and Restoring Strategy of Dynamic Voltage Restorer

Abstract: In this paper, the principle and topology of dynamic voltage restorer(DVR) are presented at first; then the principle of information detection methods in common use and their advantages and defects are analyzed, including various coordinate transformation methods for fast and accurate disturb identification, and soft phase locking method for phase acquisition. The induction and comparison of familiar compensation strategies are carried out, especially discussing the widely used minimum energy compensation with its improvement. Finally the development trend of the theory and experimental research of DVR are described.

A Survey on Commutation Failures in Multi-infeed HVDC Transmission Systems

Abstract: Commutation failures are very frequent dynamic events in high voltage DC (HVDC) transmission systems. As for multi-infeed HVDC systems, the interactions between AC and DC systems become more complicated. A failure of one inverter station may affect the operation of other adjacent inverter stations, even the power transmission of HVDC links might be consequently blocked, thus the stable operation of whole AC/DC transmission system might be affected. The authors analyze the present situation of the research on commutation failures in multi-infeed HVDC system home and abroad in detail. According to the mechanism of commutation failure, influencing factors and judgment basis, the authors research the prevention measures and control strategies proposed in recent years and their applications, and point out that following issues should be researched henceforward such as the establishment of AC/DC system model which can exactly reflect the commutation process, the analysis on commutation failures in multi-infeed HVDC transmission system, the drafting of effective control measures and recovery strategies as well as the impact of harmonics caused by commutation failures and so on.

Additional Control Strategy for Islanded AC System at Sending Terminal of HVDC

Abstract: When HVDC project is used for the power transmission from large hydropower station or thermal power plant located far away from the main power grids, the AC power system at sending end falls into an islanded system. In the circumstance, the conventional control mode of constant power or current may cause persistent power unbalance in the grid while the AC system is disturbed, and then leads to the instability of AC and DC systems. The authors propose an additional control strategy, which changes the power or current order according to the variation of system frequency, thus the power balance of the grid can be implemented. To verify the proposed control strategy, real-time digital simulator is adopted. Simulation results show that the proposed additional control strategy can evidently enhance the stability of power grid.

A chance-constrained programming approach to determine requirement of optimal spinning reserve capacity

Abstract: Under the premise of chance-constrained programming,when the consideration to reliability and economy of system operation should be given,how to consider the uncertainty factors such as the fault outage of generators and the error of load forecasting is researched so as to determine the optimal spinning reserve capacity that power system requires.Taking the purchase cost of minimized spinning reserve as objective as well as the secure requirement of power system as chance-constraint,a mathematical model to determine optimal spinning reserve capacity required by power system is constructed,and Monte Carlo simulation based genetic algorithm is adopted to solve the constructed model.Taking a power system containing 18 generating units for example the proposed model is illustrated.

Investigation on Tower Collapses of 500 kV Renshang 5237 Transmission Line Caused by Downburst

Abstract: In all kinds of natural disasters jeopardizing transmission lines, intense storm is the most minatory one, the accidents and failures in high voltage transmission lines and the damage to transmission towers caused by intense storm occur now and then. The authors firstly present the result of field investigation on the failures that ten towers of 500kV Renshang transmission line 5237 collapsed and the flashover of 500kV Renshang lines 5237 and 5238 of East China power grid occurred, those failures were caused by the downburst which hit Siyang County , Jiangsu province on June 14th, 2005. According to the order of severity of transmission tower collapse, the collapsed towers are classified; the destruction characteristic of downburst and its damage to transmission lines are analyzed. The results of preliminary analysis on the reasons of tower collapses show that the extraordinarily intensive downburst is the principal cause of these failures; the quantity of diaphragms designed according to the current design specification for transmission towers to resist wind is insufficient and the dynamic coupling effects between transmission towers and conductors cannot be neglected.

Impact of Transmission Line’s Real-Time Reliability Model Parameter upon Power System Operational Reliability Evaluation

Abstract: By use of the concept of operational reliability and evaluation theory, a component’s reliability model based on real-time operating condition is built, in which the impacts of units’ operating mode, real-time fluctuation of power load and variation of power network structure on operational reliability are comprehensively considered. On this basis the modeling principle for component’s real-time reliability is proposed, the hyperbolic function model of transmission line is given, the impacts of the parameter variation of real-time reliability model of transmission line, such as probability statistics of transmission line outage, power flow off-limit threshold of transmission line, rated capacity of transmission line and so on, on evaluation results as well as on the model itself are analyzed in detail, furthermore, the method to choose the parameters of practical real-time reliability model of transmission line is put forward.

Principle of Interfaces for Hybrid Simulation of Power System Electromagnetic-Electromechanical Transient Process

Abstract: If the electromechanical transient simulation for a large scale power grid and the detailed electromagnetic transient simulation for a specified part of power grid can be simultaneously realized during a single power system simulation process,such a simulation method will possess great theoretical and practical significances in the detailed analysis of system characteristics,especially in the analysis on characteristics of HVDC power transmission and components of FACTS.For this topic,on the basis of comparing the models and method for electromagnetic transient simulation and those for electromechanical transient simulation the authors propose a general interface method for hybrid simulation of power system electromagnetic transient and electromechanical transient processes.The effectiveness and practicality of the proposed simulation method are verified by its successful application in domestic actual power grids.The models,method and corresponding implementation cases of the hybrid simulation will be described in three serial papers.Here,in the first one of these papers the principle to implement the hybrid simulation of electromagnetic-electromechanical transient process and its interface models,e.g.,the design of equivalent circuits and interchange time sequence of the interfaces,are presented.

Preliminary Analysis of Large Scale Blackout in Western Europe Power Grid on November 4 and Measures to Prevent Large Scale Blackout in China

Abstract: The “11.4” blackout in Western Europe is a large outage in European history. The development and recovery process of this outage is introduced here. According to the investigation reports of the “9.23” Sweden–Denmark blackout and “9.28” Italy blackout and “11.4” Western Europe blackout, the results of these investigations are analyzed. Based on these blackouts some problems in European power grid are indicated. Suggestions for developing new technologies to prevent large scale blackout in China are presented.

System Architecture of Digitized Substation

Abstract: The system architecture and design principles of digitized substation are expounded and the technical fundamentals for the proposed system architectures are analyzed. The basic scheme of network composition for process bus and station bus are presented. Digitized substation architectures with high reliability are proposed in the matter of functional redundancy and network fault tolerance, and the solutions for the connecting of conventional devices are put forward in the process level and bay level.

A Survey on Fault Location Methods for Hybrid Transmission Lines Consisting of Power Cables and Overhead Lines

Abstract: In view of the structure and features of hybrid transmission lines consisting of power cables and overhead lines, the authors enumerate several fault location methods suitable to hybrid transmission lines, including section fault location method based on distributed parameters model, two-terminal travelling wave based fault location method based on normalizing wave speed algorithm, one-terminal travelling wave based fault location method with the same voltage pulse imposed on three-phase buses, etc. Analyze the applicable range, merits and demerits of each method respectively. A preliminary evaluation on application prospects of these fault location methods is given.

A Survey on Methods to Distinguish Permanent Faults from Instantaneous Faults in Transmission Lines

Abstract: The current situation of the research on distinguishing permanent faults from instantaneous faults in transmission lines is presented. There are two methods to distinguish instantaneous faults from permanent faults: one is based on restore voltage in instantaneous faults; the other is based on arc characteristic in the instantaneous faults. As for the former, its distinguishing accuracy is influenced by the reliability of secondary circuits of PT, and this method cannot be used in the transmission lines where shunt reactors are installed due to the low restore voltage; as for the latter, for the arc voltage is lower than 5% of the rated voltage, so its confidence level is low in measurement, analysis and judgment, and whether the existence of arc could be equivalent to instantaneous fault or not is still a problem to be researched. For this reason, a new idea, i.e., according to the currents in shunt reactors during the stage of voltage recovery to distinguish the permanent faults from instantaneous faults, is proposed to solve the problem of adaptive autoreclosure of transmission lines with shunt reactors.

A Preliminary Research on Power System Cascading Contingency Forecasting

Abstract: In recent years, cascading contingency become important cause leading to large-scale blackout of power grids, so it is of significance for prevention of large-scale blackout to effectively forecast the following-up failure that could occur. On the basis of analyzing the evolution law of a cascading accident during the initial stage in detail, a method by which the following-up failure can be forecasted is proposed. This method can effectively take the interaction between previous failure and following-up failure into account as well as the cumulative influence of all happened faults, and rapidly forecast following-up failure that could occur. This research is an attempt to seek an effective method for prevention of large-scale blackout.

Short-Term Load Forecasting Based on Attribute Reduction Algorithm of Rough Sets and Support Vector Machine

Abstract: A short-term load forecasting model based on two integrated intelligent algorithms, ie, attribute reduction algorithm of rough sets and support vector machines (SVM), is proposed At first, according to historical data a attribute decision table is built up and the data mining is performed by means of attribute reduction algorithm, thus the kernel factors influencing loads is determined and using them as the input vectors of SVM the load forecasting is conducted Forecasting results of calculation examples show that comparing with traditional SVM model that chooses input vectors in the light of experience the forecasting accuracy is evidently improved and is more suitable to short-term load forecasting

Study on Impacts of UHVDC Transmission on Power System Stability

Abstract: UHVDC transmission schemes of the chain hydropower stations along Jin Sha River and Ya Long River are studied. Around 2015, East-China, North-China and Central- China synchronous power grid will receive large amounts of power through several UHVDC transmission lines. The impacts of large capacity UHVDC transmission on multi-infeed AC/DC systems are emphasized in the study. The security and stability of whole system and interactions among AC and DC systems are studied under the emergency cases, such as monopolar/bipolar block faults of UHVDC systems and single or double AC faults near UHVDC converter stations. Considering different system conditions, such as installing SVC devices, changing load characteristics or increasing DC power modulation, sensitive analysis of system stability under UHVDC bipolar block faults are also carried out.