Showing papers in "Electric Power in 2011"

Fracture mechanism and defect detection methods of 500 kV composite insulators

Abstract: The fracture of composite insulator imposes great danger to the operation safety and stability of overhead transmission lines.Based on an example of fracture of 500 kV composite insulators,the mechanism of fracture is analyzed.The application effect of infrared thermal image and ultraviolet corona on defect detection is discussed.The results show that,the decrease of mechanical property of core rod resulted from the combined effect of local strong electric field and weak acid corrosion is an important reason for the fracture of composite insulator.The online detection technologies such as infrared thermal image and ultraviolet corona,which has merits such as long-range,non-contact,accurateness real-time and quickness,can be used to detect the defects of composite insulator effectively.To avoid the fracture accident of composite insulator,it is necessary to optimize the structure of grading ring,to choose the optimal grading ring diameter and the installation location,to improve the nonhomogeneity of electrical field and voltage distribution along the surface of composite insulator so that the corona discharge phenomenon in local area of composite insulator can be inhibited.

China wind power integration status quo and its benefit to energy saving and emission reduction

Abstract: Based on the research of wind power development policies,the reformatory direction to overcome the disadvantages of the policies was proposed.The wind power's grid integration status quo was introduced,and the bottle neck of grid integration was analyzed.The study results on the economic benefits of the wind power integration in China's present stage indicate that the wind power industry is in good profit condition.The profit levels are higher in areas with the richer wind resources.Expanding the margin of the power purchase prices in different resource areas is beneficial to the nationwide proportionate development of wind power.At last,the present and future benefits for the energy conservation and emission reduction from the wind power integration were estimated.The forecast result indicates that the environmental benefits of "wind-thermal exchange" will be increased along with the expansion of the using scale of wind power.

Wind power prediction achievement and prospect

Abstract: Wind power prediction is important to the operation of power system with large amount of wind power.The current situation of wind power prediction technology,wind power prediction system construction,prediction errors,assessment index and main market body of prediction were discussed from the power dispatch perspective.The main problems of incomplete basic data,low prediction precision,prediction time scale short and lack of prediction in most wind farms were analyzed.Some improvement suggestions were proposed,such as enforcing wind power prediction system construction both on grid side and wind farm side,speeding up the building of ultra-short term wind power prediction system,deepening wind power prediction technology study and strengthening prediction technical standard system and cooperation of different industries.

Research and application on communication technology in smart distribution and utilization grid

Abstract: The network communication technology for smart distribution and utilization grid is discussed comprehensively.The main contents include overview of smart distribution and utilization network,the communication requirements of backbone network and access layers,distribution automation communication protocol,EPON network,broadband power line communications(BPLC) and the power wireless broadband system based on TD-LTE technology.The intelligent distribution and utilization business requirements are introduced to provide technical guidance for intelligent distribution communications networking solution.The data transmission in intelligent distribution has several distinctive features,including complex network,large number of scattered nodes and complex business types.A comprehensive communication solution for integrated distribution and utilization is proposed.The solution adopts optical fiber communication for backbone network,wireless broadband and passive optical communications for the global coverage,special low-power photoelectric composite cable,power line communications and short-range wireless communications for main terminal access.The proposed solution provides efficient,secure,real-time and two-way communication support for the strong unified smart grid.

Analysis of State Grid security operation in 2010

Abstract: In 2010,with the challenges of growing power demand,frequent bad weather and densely-scheduled new facility commissioning, SGCC tackled all the difficulties to safeguard the safe and stable operation of the grid,and fulfilled the major tasks of ensuring power supply to the World Expo in Shanghai and commissioning of the UHVDC demonstration project.The grid security and stability have been greatly improved.The statistics and analysis of the transmission system faults occurred in 2010 concludes that the weather conditions and the equipment quality are the main causes of system faults.Suggestions are given in order to answer the challenges of power security and to strengthen the supervision and management of the power dispatching system with the fast development in UHV interconnected network.

Design and implementation of microgrid protection systems

Abstract: There are many distributed resources existing in microgrids,which may cause the traditional stepping over-current protection to fail.To address this issue,an industrial computer based laboratory microgrid protection system was designed,in which a data acquisition card was used to obtain data with a high speed for the identification of fault types and their regions,thereafter,the protection system would clear faults according to the variations in voltage parameters and fault directions,protecting the microgrid against the fault under grid-connection operation and islanding operation modes.By taking a laboratory microgrid for example,the microgrid protection algorithm was explained briefly,and the hardware infrastructure and software development process were described.Finally the feasibility of the protection system was analyzed.

Influence of atrocious weather on transmission lines of Zhejiang electric power grid

Abstract: Atrocious weather imposes great danger to overhead transmission lines operation safety and stability in Zhejiang electric power grid.The ice disaster,windstorm disaster and lightning trip occurred in Zhejiang electric power grid are discussed in detail.The reasons for the transmission lines faults are analyzed.Besides,the measures and advices for the prevention of the transmission lines from those weather phenomena are presented.It provides reference for the future disaster prevention work.The results show that,the overload,imbalanced tension,and insulator icing flashover,which are resulted from the severe icing,are the main reasons for the icing disaster.For the new constructed transmission lines,the micro-terrain and micro-climate areas such as mountain pass,watershed,lakes and gorges should be avoided.The overload of transmission tower due to the severe typhoon is the main cause of the tower collapse.For the new constructed transmission lines,the original meteorological partition should be revised and refined,and the anti-typhoon standard of overhead lines should be increased appropriately.The lightning disaster in Zhejiang has regional distribution characteristic.It is recommended to install line arresters and other devices to reduce the lightning trip rate.

Mechanism of T23/12Cr1MoV dissimilar steel welding failure in high temperature reheater

Abstract: Fracture mechanism of T23/12Cr1MoV dissimilar steel welding in high-temperature reheater operated for 8 000 hours in the 1 900 t/h boiler was researched by means of macro-morphology analysis of crack characteristics,hardness test and metallographic examination.The results show that the martensitic organization become hardened in the weld and the heat affected zone without preheating and heat treatment after weld,and the grain boundaries became weakening because of grain coarsening in coarse grain zone.On the condition of higher temperature, welding residual stresses and high steam pressure of pipes,the stress concentration in the interfacial of welded joint and coarse grain zone was accelerated.With the increasing of applied stress plasticity,the crack between the grain boundary of coarse grain zone and welded point was emerged.The reheated cracks are the main reason for the welding failure of T23/12Cr1MoV dissimilar steel in high-temperature reheater.

Two kinds of typical coordinated control systems in ultra-supercritical units

Abstract: The coordinated control systems of 1000 MW ultra-supercritical units in China can he classified as two typical types:coal following water control and water following coal controlALSTOM used water following coal control structure and HIATCHI/MITSUBISHI used coal following water control structure assisted with dynamic feed forward controlThe theory and structure of the two types of coordinated control systems were analyzedApplications show that both the two types of control systems can get satisfied control performance

Optimization test of blending radio between typical lean coal and anthracite

Abstract: When coals with different combustion properties to be blended,the blending radio will do great influence to the fire behavior,the burn-up property,and the coking characteristics of the blended coal.In the laboratory,the competitive test is carried through to analyze the changes of the ash component,the grindability,the abrasion index under different blending ratio between typical lean coal and anthracite.Combustion characteristic curves under different blending ratio were obtained using thermo gravimetric analyzer.The test result shows that the combustion performance,the grindability,and the coking characteristics are deteriorating with the increasing of the ratio of anthracite.Considering the coal price,there exits an optimal ratio between the lean coal and the anthracite.The research provides a method to optimize the ration of different blending purpose.

Study on index weighting methods for transformer condition evaluation

Abstract: Transformer reliability is pivotal to the power system security and stability.Accurate and real-time data acquisition regarding transformer's operation condition is essential for making the maintenance plan and evaluating the system risk.After analyzing parameters for condition evaluation,a combined weighting method was proposed based on the entropy and improved analytic hierarchy process(IAHP) and it's validated by the field data.

Kurtosis analysis of wind speed time series based on SV model

Abstract: Wind speed forecasting is one of the most important issues in the domain of wind power generation.Wind speed changes irregularly and fluctuates violently,which makes it difficult to be forecasted.Comprehensive investigation on characteristics of the wind speed data is a positive key solution to improve the precision of wind speed forecasting.With the technique of stochastic volatility(SV) model kurtosis analysis,the leptokurtosis of wind speed was developed.Based on the specific definition of kurtosis in power systems,the extended SV excess kurtosis theorem was induced and proved.SV models were built adapting to the wind speed characteristics.In the case study,SV models with different conditional distributions were also presented and the overall kurtosis of wind speed was analyzed.In addition,a feasible scheme based on the SV-t type models for choosing the best conditional distribution in SV wind speed forecasting model was proposed.Results of the case study based on actual wind speed data demonstrate clearly that the proposed model is a valid method for wind speed modeling with the consideration of the wind characteristics of excess kurtosis and can provide a promising way for the practical wind speed modeling.

Enhancing response speed of primary frequency regulation in thermal power unit

Abstract: Fast response speed is required for the primary frequency regulation based on its role and functions.The necessity was analyzed on the base of principle and function of frequency regulation.Systemic control strategies were proposed to enhance the response speed of primary frequency regulation.Application results of the units in Guangdong province showed that the proposed strategy improved the quality of primary frequency regulation.It is valuable for the similar units to enhance their primary frequency regulation performance.

Annual energy production calculation in wind farm based on physical model

Abstract: Annual Energy Production(AEP) is an important index in quantitative benefit evaluation of planned wind farm.The real situation cannot be reflected by existing AEP calculation methods accurately,especially in complex terrain area.Influencing factors of AEP in wind farm were analyzed;physical models such as roughness model and terrain model were introduced.With the consideration of wind electrical field local effort influence on the wind resources,an analytic method was proposed to analyze the local effect of wind farm and wake effect of wind turbines.The proposed method can provide accurate simulation of wind resources in planned wind farm,which can in turn better evaluate the benefits in the planning stage.

Analysis of explosion accident for a 35 kV current transformer

Abstract: With comprehensive knowledge such as the high-voltage engineering,relay protection and circuit theory,the pseudo morphs resulted from current transformer(TA) primary current leak into secondary windings are ruled out and a complete process of TA explosion accident is reproduced.An accurate accident analysis method and prevention measures for similar accidents are proposed.The correct secondary windings order is required to avoid the increase of the fault current duration during TA short circuit.Otherwise,the TA short-circuit may bring more serious damage to other electrical equipment and system stability.The power outage range also expends greatly for line TA fault.

Dynamic reactive power compensation device based on magnetically controlled reactor

Abstract: The current research of substation reactive power compensation is reportedThe application prospect of magnetically controlled reactor(MCR) in reactive power and voltage control is analyzedThe property of MCR and Substation power compensation principle is analyzedA dynamic reactive power compensation device is developed based on MCR's ability to adjust reactive power output smoothlyA control system with four control modes is designedSimulation results show the device is effective in voltage fluctuation inhibition and reactive power compensationThe 220 kV substation operation results show that the control system is reliableThe compensation device can adjust the reactive power output smoothly,respond to system voltage and reactive power requirements rapidly and improve system voltage quality and reactive power distribution

Implementation of the smart grid in China:challenges,issues,and actions

Abstract: Smart grid is the new technology revolution in today's crisis transition era.The construction of China smart grid is facing a series of challenges and upcoming new issues.These challenges and issues mainly include:construction and development of China smart grid must be lead by government;actively track existing and emerging smart grid communication,monitoring and control technologies;accelerated construction of smart grid interoperability framework;advanced metering infrastructure(AMI)onstruction with high priority;distributed smart grid control methods;smart grid ICS/MCS cyber security;development of demand side technology such as Home-Area Networks (HAN) construction and smart appliances interface standardization;fully understand the competition environment in smart grid.These challenges and issues requires feasible,scientific,effective,comprehensive and long term development planning within the scope of national laws and regulations to ensure the healthy development of the smart grid.The construction of China smart grid will not be successful without solving those challenges perfectly.

Neural network model for short-term wind power prediction based on phase space reconstruction

Abstract: With the lasting rapid increase of wind turbine capacity and the large-scale wind farm construction,the degree of recognition on wind power in different countries or regions' power grids is also increased.The short-term wind farm generation prediction plays an essential role for the wind farm access and power grid dispatch.the analysis on time series of wind farm generating capacity shows its chaos characteristic. Based on chaotic theory,phase space reconstruction method is used in RBF neural network and BP neural network to predict wind farm generation in short-term.The comparison and analysis of the prediction results show that RBF neural network has a more accurate prediction.

Multi-Agent fault diagnosis method based on dissolved gases in transformer oil

Abstract: The current transformer fault diagnosis system has problems including simplified model,weak adaptability and prone to error or miss diagnosis.In order to solve these problems,a collaborative transformer DGA model used for intelligent fault diagnosis system based on multi-Agent system is proposed.The paper presents the main function of each Agent,blackboard and JADE bus in this model,discusses the collaborative process of intelligent fault diagnosis system for transformer DGA based on multi-Agent system,puts forward an expert voting diagnosis algorithm based on multi-Agent and a competitive algorithm for resource based on Blackboard method.The application examples show the feasibility and effectiveness of the proposed method.

Search algorithm of black start initial scheme

Abstract: A new searching algorithm for black start initial scheme based on deep first search(DFS)is proposed to avoid the difficulty to prepare such scheme manuallyIn order to reduce the search space,the black start path rules are summarized based on the rational scheme requirement Several improvements are applied to the search strategy to guarantee the completeness during route searchThe improvements are in three aspects,such as adopting forward search terminate criteria,completing child nodes processing and taking load priority into consideration to ensure path passes through important loads as many as possibleTherefore,the presented algorithm has the ability to find complete initial black start scheme within limited timeThe testing results from practical system demonstrate the validity and effectiveness of the algorithm This algorithm lays a good foundation for the automatic system black start scheme formation

Wind power control considering system frequency regulation

Abstract: With the rapid increase of the wind power capacity,the difficulty of system frequency regulation is more apparent than ever due to the volatility and randomicity of wind power.A power regulation method for wind turbines and wind farms,considering their regulation characteristics and the stratified feature of system frequency control,is established.This stratified regulation strategy is based on the real-time system frequency deviation.Simulation results show that by using the proposed method,a wind farm can quickly and effectively regulate its output to support the system frequency stability according to the system frequency regulation demand and shorten the duration of the abnormal system frequency.

Transient voltage stability study about a regional grid integrated with wind power

Abstract: With the increasing share of wind power in a power system,the impact of its integration cannot be ignored.A regional grid which has a lot of wind resources is mostly not strong.Combined with the reactive power performences of wind farms,the voltage stability of the grid with wind farm integration is particularly important.The transient voltage stability of the grid was analyzed for the cases of integration with DFIG(doubly fed induction generator) based wind farms and IG(induction generator) based wind farms.The critical clearing time points of fauts at various power outputs were given by DigSILENT simulation.The improvement of transient voltage stability of IG based wind farms by dynamic reactive power compensation devices(SVC and STATCOM) was studied also.

RT(NDT) drop weight test of no ductility transition temperature for 12Cr2Mol alloy steel forgings used for the reactor internals in nuclear power station

Abstract: 12Cr2Mo1 alloy steel forging material is widely used for reactor internals in the demonstrate project of high temperature gas-cooled reactor nuclear power plant.In order to avoid the failure of properties of the material during the service life cycle of the reactor,drop weight test under the condition of RTNDT≤-25℃ was required for the material manufacturing.Chinese manufacturers have less experience in the manufacturing before the project.To master the key manufacturing technique,experiments and research were carried on.The quality problems occurred in the manufacturing of the material,the cause analysis,improvement approach,and the achieved effects were introduced,which will provide a good experience for the domestic material application in 1 000 MW high temperature gas-cooled reactor nuclear power plant.

Stability analysis and visualization study of wind power integration

Abstract: Fast development of large-scale wind power farms and their integration affect power grid stability.The impacts of wind turbine tripping on the grid frequency and requirement for low voltage ride through(LVRT) capability of wind turbines were discussed.The simulation of the WSCC 3-machine 9-bus system by visualization technology conveyed the grid voltage trajectories during tripping disturbance.Moreover,the qualitative analysis of LVRT was made for integrated wind turbines.Simulation results proved that visualization technology based on PowerWorld will assist operators in system monitoring during the disturbance.

Short-term wind speed forecasting based on SVM time-series method

Abstract: Short-term wind speed forecasting is of significance for the operation of grid-connected wind power generation systems.An accurate wind speed forecasting can effectively reduce or avoid the adverse effect of wind farm on power grid and strengthen competition ability of wind farm in electricity market.A new application of the Support Vector Machine(SVM) theory is introduced.The detailed process for SVM usage in wind forecast process is discussed.A SVM wind speed forecast model for wind farm is founded.This model,which only uses historical wind data as input,is simple and effective compared to other models which need additional meteorological data.The comparison of SVM forecast results with other forecast models such as improved fuzzy analytical hierarchy process model,ARMA-ARCH model,EMD-ARMA model and double ARMA models proves the validity of the proposed model.It can be used in the short-term forecast and power generation prediction effectively.

A practical energy-saving generation dispatching model integrated with wind power

Abstract: The problems related to energy-saving generation dispatching are analyzedBy the introduction of emission reduction coefficient and desulfurization correction factor,a new dispatching index with consideration of coal consumption and emissions is proposedAn energy-saving generation dispatching model integrated with wind power is introducedThe new model enhanced traditional model with modified spinning reserve constraints and additional instantaneous speed climbing constraintBy simplifying the objective function and various constraints and introducing the network loss factor to simplify network security constraints,the practical model is establishedNumerical example shows that practical treatments can greatly improve the calculation speed which has important practical value

Pitch control of doubly-fed variable-speed and variable-pitch wind turbine units

Abstract: For a large doubly-fed VSVP(variable-speed and variable-pitch) wind turbine to maintain stable power output and reduce tower vibration,a nonlinear torque control strategy was proposed based on the traditional pitch control method.To reduce tower fore-aft and side-side vibrations,the acceleration-based pitch and torque control strategy was put forward and the simulation was made on the proposed control strategy for a 2 MW VSVP wind turbine with Bladed software.Study results indicate that the proposed strategy can better stabilize power output and reduce tower vibration and load than the traditional method.

Study on algorithms of power curtailment among wind farms

Abstract: When the wind power output is larger than the maximum system transfer capacity,wind power curtailment is required for operation safety.The smooth effect in multiple wind farms should be considered in power distribution.Five different wind curtailment algorithms were proposed based on the availability of wind power forecast system in a wind farm,and the models were established.The wind power outputs and losses were simulated according to hour-ahead power prediction data.Study results indicate that compared to other algorithms,the power generation models with consideration of forecasts have significant advantages.The test results are useful in decision optimization of wind power dispatching.

Impact of large-scale wind power on operation stability and security of connected Jiangsu grid

Abstract: Large-scale wind farms bring new challenges to the operation of connected Jiangsu grid.It is necessary to analyze the impact of large-scale wind power on the grid operation security and stability.Based on the overall planning data of Jiangsu power grid and its wind power in 2015,the impact in different proportion of wind power on power flow distribution and voltage stability was analyzed.According to power flow calculation results with the N-1 rule,the limit clearing time of heavy-loaded lines under faults was conducted and the grid transient stability was assessed.Some measures were proposed to improve grid operation security and stability.

Analysis and solutions for energy-saving generation dispatch of Jiangsu power grid

Abstract: Energy conservation and emission reduction can be achieved by a optimal allocation of generator load with energy-saving generation dispatch strategy.The start-up and shut-down of generator,regulation ability of generator,period coupling,grid loss and generation substitution are analyzed in detail for the improvement of Jiangsu generation dispatch.The solutions for the problems are also investigated.The practical data from Jiangsu power grid indicate that energy-saving generation dispatch is effective in decreasing coal consumption comparing with impartiality and openness generation dispatching mode.Furthermore,the stability and power flow issues resulting from energy-saving generation dispatch are analyzed in detail.Finally,the feature of Jiangsu energy-saving generation dispatch is presented comparing with the dispatching mode of Zhejiang power grid.