Showing papers in "Electric power automation equipment in 2010"

Prediction of electrical equipment failure rate for condition-based maintenance decision-making

Abstract: As the electrical equipment failure rate calculated by post-failure statistic analysis has low reliability,a way to predict electrical equipment failure rate is introduced,which is based on the actual operating state of equipment and the relevant evaluation rules. The health index is adopted to quantify the equipment deterioration,which is used to extrapolate the current equipment failure rate and determine its actual service age. The Marquardt method is used to deduce the failure rate function and the Weibull distribution is combined to piecewise fit the curve. The age reduction factor is introduced to describe the repair extent,the equivalent service age of the equipment after maintenance is then determined and its failure rate is predicted,which supports the follow-up implementation of optimized condition-based maintenance for multiple devices. Case study shows the effectiveness of presented method.

Energy Internet system based on distributed renewable energy generation

Abstract: Based on distributed renewable energy generation,an energy Internet system is constructed,which enables the real-time,high-speed,bi-directional access of electric power data and the grid-paralleling of renewable energy sources The energy Internet system consists of IEMS(Intelligent Energy Management System),distributed renewable energy source,energy storage,converter and intelligent terminals,etc Besides the normal energy management,IEMS provides a visual operating platform to realize the "plug and play" of renewable energy sources and the switchover between networking and island operations Energy storage is indispensable in improving the power quality,enhancing the system stability,reserving the energy and increasing efficiency The power electronic transformer is used to satisfy the paralleling requirements of renewable energy generation It is concluded that the main research fields of energy Internet are the control strategy,power electronic converter technology and energy storage technology

Modeling of DC micro-grid and stability analysis

Abstract: The average models of various converters and their control systems are established by state-space approach,based on which the small disturbance stability of DC micro-grid is analyzed to obtain the loci of system eigenvalues versus converter control parameters. It shows that,when control parameter increases to a certain value,the real part of eigenvalue becomes positive,i.e. the system becomes instable. The time-domain simulation is carried out to obtain the voltage curves under different control parameters,which validates the practicability of proposed analysis method. It also shows that,within the stable range,the larger the control parameters are,the better the voltage control performance is. It is concluded that,the proper setting of converter control parameters ensures the voltage stability of DC micro-grid.

Overview of power system wide area protection

Abstract: The existing problems of traditional protections are analyzed and the main contents involved in the study of protection based on wide-area information are reviewed,including:on-line adaptive setting,flow transfer identification and wide area backup protection based on fault component identification. The on-line setting is to adjust the protective settings to the optimal state according to the change of system operation modes,including the change of electric device on-off state and the change of generator output and loads. The flow transfer identification is to prevent the improper protective actions which may lead to cascading trips,including the comparison of transmission section active powers and adjacent branch currents before and after branch break. The wide area backup protection utilizes multiple node measurements to locate the fault component,which has easier protection setting and higher reliability than the traditional back-up protection,including the fault identification algorithm based on traditional main protection theory and the information error tolerance algorithm. A wide area protection system based on wide area back-up protection is presented for smart grid and its development trend is prospected.

Chaotic characteristics identification and trend prediction of running state for wind turbine

Abstract: The nonlinear dynamic model is built for the chronological state parameter series of wind power generator set,the dynamic characteristics of its running state are analyzed and its chaotic characteristics are verified,based on which its chaotic prediction method is studied according to the phase space reconstruction theory.The proposed weighted first-order local prediction method is tested with the actual operational data of a wind power generator set and the results show that,the chaotic prediction method is feasible with higher precision.

Problems and solutions of power system out-of-step islanding

Abstract: In order to analyze the problems of traditional out-of-step islanding,three criteria widely used in domestic power systems are introduced.It is pointed out that,the out-of-step islanding devices based on these criteria detect the out-of-step of system by the indirectly reflecting power angle.The traditional islanding scheme with the apparent impedance criterion is applied in the out-of-step islanding simulations for a 2-machine system and a provincial system.Simulative results show some defects:the generation-load imbalance in each island can not be as small as possible,the installed islanding equipment becomes invalid because of the oscillation center transfer caused by the operating mode change,the separation surface determined based on the offline simulation or experience could not adapt to the change of out-of-step mode,and so on.For the safety and stability of power system,an adaptive out-of-step islanding control system based on global real-time information is studied and its four aspects are summarized.

Discussion about information and communication technology of smart grid

Abstract: ICT(Information and Communication Technology) is one of the key issues of smart grid and the basis of its realization. The information flow of smart grid consists of four layers:equipment layer,communication network layer,data storage management layer and data application layer. The ICT standard of foreign smart grids is introduced and it is pointed out that the study of the standard system for electricity supply should be strengthened. The main problems existing in China's power communication network are discussed and the architecture of information and communication system for smart grid is proposed. The information security of smart grid is discussed and the security defense of wireless network is emphasized.

Variable-speed wind turbines provide primary reserve for frequency control

Abstract: A frequency control strategy is presented,which utilizes the fast response capability of VSWT to actively provide the primary reserveIt unloads the wind turbine to ensure the primary reserve for a large range of wind speedAt low wind speed,the wind turbine operates as a flywheel to utilize the kinetic energy stored in the rotational masses for the temp active power supportAt middle wind speed,the wind turbine operates according to the unloading optimal energy conversion curve to set up the active power reserveAt high wind speed,the wind turbine operates with full load at the modified rotor speed set point or under the pitch control to keep an appropriate active power reserveSimulative experiments indicate its effectiveness in the power reserve control for frequency control

Remote online monitoring system of power system lightning current

Abstract: Remote online monitoring system of power system lightning current is a data acquisition equipment of natural lighting current waveform for power system, which applies the Rogowski coil to transform the lighting current to voltage signal and realizes the high-speed data acquisition and wireless data transmission of lightning current waveform. Special server software is used to display waveform and determine the lightning type and fault mode. The equipment is installed on transmission line or lightning rod. Four sets of lightning current waveforms have been recorded during 2 years' field operation. Compared with the laboratory impulse current waveforms, the natural lightning current waveforms have the wave head of less than 1 μS and the violent vibration of wave amplitude.

Single-stage full-bridge PFC technique based on clamp circuit

Abstract: Because of the leak inductance of transformer,the power switch on-off operation of single-stage full-bridge PFC(Power Factor Corrector) generates high over-voltage,which increases the voltage stress of power switch and lowers the stability of corrector The PFC based on clamp technique is presented,which realizes the power factor correction and DC/DC conversion with single stage structure The over-voltage is absorbed by the clamp circuit and the voltage stress is lowered Its working principle is explained Based on the structure of PFC,the mechanism of magnetic bias generation in the high frequency transformer is analyzed and the countermeasures are presented Experimental results show that,the proposed PFC achieves higher power factor and DC/DC conversion efficiency,which verifies the validity of the theoretical analysis

Control strategy of grid-connected photovoltaic generation system based on modified MPPT method

Abstract: The control strategy of single-phase two-stage grid-connected PV(Photo Voltaic) generation system is studied and improved.A duty cycle perturbation MPPT(Maximum Power Point Tracking) algorithm is proposed based on two basic MPPT methods,which integrates CV(Constant Voltage) tracking and IC(Increment Conductance) tracking.Different tracking approaches are applied at different operating points and the duty cycle of DC chopper is directly controlled to achieve the optimum control results.The control strategy of PV generation system is improved to meet the requirements of the proposed algorithm.A DC voltage outer loop control for power balance and PI correction and an AC current inner loop control for feedback are designed to ensure the current quality and stabilize the DC voltage.A simulation system is built with PSCAD / EMTDC to verify the validity of the modified MPPT algorithm and the converter control strategy.

Development of relay protection for smart grid(1):new principles of fault distinction

Abstract: As the fault transient components have same power directions at both line ends and great transient energy during internal line faults,they can thus be extracted by the wavelet transform and applied in the ultra-high-speed protections for EHV transmission line and bus.When the DC filter and smoothing reactor are installed at the ends of DC line to form an impedance boundary of high frequency components,which makes the high frequency components of internal fault signals much greater than those of external ones,the energy of them can thus be used to realize the ultra-high-speed protection for UHVDC transmission line at single end.As the transient zero-sequence component is several ten times larger than the power frequency component and not reduced by the compensation during the single-phase-to-ground fault in a neutral indirectly grounding power system,the high frequency component of zero-sequence current is thus extracted to realize the grounding line selection by comparison of direction and amplitude.Tests show that the fault kind can be determined with ultra-high-speed(within 5 ms) and the new principles of fault distinction can satisfy the demand of EHV system for ultra-high-speed fault removal in smart grid.

Prospects of visualization under smart grid

Abstract: The development state of smart grid and power grid dispatch is analyzed,and combined with the latest achievements of computer science,the important role of dispatcher in new intelligent dispatch system is describedThe intelligent dispatch architecture "with the dispatcher thinking mode as the framework,the visualized interface as the function module and the interactive computation as the system core" is proposed,which adapts to the characteristics of power grid in multiple dimensions and carries out the coordination of different partiesThe key technologies of intelligent dispatch construction are pointed out in different aspects:man-machine integrated decision-making model,data fusion,situation visualization,fast simulation and modeling,intelligent warning,intelligent dispatch and backup system,emergency center integration,dispatcher behavior assessment,etc

General microgrid model based on physical background

Abstract: Microgrid is a small power system,composed of loads,DG(Distributed Generators) and storage devices,and connected to the power network via common coupling point.Power flows bidirectionally between microgrid and power system.It is necessary to build the microgrid model for studying its connection to power network.The relation between the load and DG models of microgrid and the element models of traditional power system is analyzed and the general microgrid model is developed based on the load modeling theory.The static elements of load and DG with static exterior characteristic are represented as the equivalent static model,for which the exponential function model is recommended,and the dynamic elements of synchronous generator,wind generator and motor load as the equivalent machine model,for which the universal equivalent machine model is theoretically derived.

Power transformer condition evaluation based on support vector regression

Abstract: To improve the accuracy of transformer condition evaluation,its health status is divided into five levels.Since SVM(Support Vector Machine) has good fitting ability for small sample set and the transformer data has the features of less samples and poor information,a condition evaluation model based on SVR is proposed for power transformer.The transformer dissolved gas analysis data and electrical test data are used to determine the scores of transformer parameters by the semi-mountain model and the results of scoreevaluation are taken as the independent variables of SVM.The multi-layer dynamic adaptive algorithm is used to optimize the parameters of SVR to predict the changeable weights.Case study verifies the proposed model is efficient and feasible and the conclusion of transformer condition evaluation is closer to its actual condition.

Application of HF/UHF joint partial discharge analysis to on-site power cable terminal detection

Abstract: The PD(Partial Discharge) method is employed to detect the potential insulation defect of high-voltage power cable terminal. According to the propagation characteristics of different PD signals,the PD sensors are developed based on HF(High Frequency) or UHF(Ultra High Frequency) detection principle,as well as the portable detection device. On-site test is carried out. The HF current transformer couples the PD current flowing through the ground strap and the UHF sensor is induced by the radiated the PD electromagnetic waves. The portable detection device is used to distinguish the real PD signals from interferences by pulse extraction and joint comparative analysis. The test results show that the HF/UHF joint analysis improves the effectiveness and veracity of PD identification.

Design of wireless meter reading system based on ZigBee

Abstract: A wireless meter reading system is designed,which consists of ZigBee ad hoc network,GPRS network and meter reading center.ZigBee ad hoc network has three parts:data collector,data transceiver and concentrator.The ZigBee node consists of the CC2430 module,sensor,antenna,power supply and power amplifier.The concentrator applies ARM as main processor and GPRS module to achieve remote data transmission via ZigBee network.The main task of concentrator software is to monitor all ZigBee nodes and meter reading center.The designed wireless meter reading system has good performance.

Demand side management planning and implementationmechanism for smart grid

Abstract: The comprehensive benefits of DSM(Demand Side Management) project are reviewed and its private goods investment property and public goods nature are summarized,according to which proper planning frames are given for different projects,including the potential assessment model,selection model and planning model. The potential risk of different phases from capital investment,project implementation to benefit analysis is analyzed for power companies,electricity customers and energy service companies. It is pointed out that measures should be taken by government to avoid risk. The implementation mechanism combining government promotion and market competition is designed for domestic DSM projects.

Preliminary discussion on China transmission backbone in the future

Abstract: The inverse distribution of energy resources and load demands and the strategic adjustment of energy structure lead to the necessary and essential breakthroughs in the receiving-end system,sending-end system and 1 000 ~ 3 000 km transmission system of China’s future transmission backbone.The transmission backbones of EU’s "Super Smart Grid 2050" and US’s "Grid 2030" are introduced and the advantages of UHV grid to form the robust receiving-end system is explored.Suggestions to lower the outage risk of UHV grid are given:the hierarchical and partitioned system operation,the self-healing ability improvement,etc.It is proposed to build a wide-area renewable energy grid of wind farms,solar power stations and hydropower stations in North China to balance their intermittence and instability by their complementarity with DC transmission technology.The characteristics and development trends of half wavelength transmission and frac-tional frequency transmission,suitable for long-distance large-scale transmission,are discussed briefly.

Unbalanced three-phase control strategy of VSC-HVDC system

Abstract: The harmonic transfer characteristics of VSC-HVDC system in three-phase imbalance are analyzed and a dual-circuit and dual-loop current control strategy based on the detection technique of instantaneous symmetrical components is proposed for it,which acquires the sequence components of voltage and current without time delay by the instantaneous symmetrical component transformation and extends the conventional symmetrical component method in time domain.An imbalance instruction compensator is added to improve the operating characteristics of VSC-HVDC system in three-phase imbalance.A VSC-HVDC system and its control strategy are built with PSCAD/EMTDC and the simulative results show the correctness of the proposed strategy.

Power-feedforward-based control strategy of grid-connected single-phase PV system

Abstract: The traditional double-loop control strategy is analyzed according to the characteristics of two-stage grid-connected single-phase PV inverter,based on which a control algorithm with power feedforward is proposed.The output power of PV panels is added to the reference of current close-loop as power feedforward,which improves the dynamic response to the input power changes.Simulations with Matlab / Simulink are carried out and the comparison of output current response to input power change between controls with and without power feedforward verifies its effectiveness.The experimental result of 1 kW PV inverter prototype proves the correctness of theoretical analysis.

Adjustable reactor with controllable load of multi-winding transformer

Abstract: A rapidly and continuously adjustable reactor with limited harmonic output is developed,which applies thyristors and voltage source PWM inverter as the secondary load of multi-winding transformer and controls the switching of thyristors and the output current of inverter to regulate arbitrarily the equivalent primary impedance of transformerThe thyristor switching control is used for coarse adjustment and the inverter output current control for fine adjustmentThe capacity of thyristor switching winding is thus much bigger than that of inverter output winding,resulting in lower costThe experimental results show the continuous adjustment and limited harmonics of the novel adjustable reactor

Power flow algorithm for distribution network with distributed generation

Abstract: After the DG(Distributed Generation) is connected into the distribution network,it has multiple power sources and DG can not be treated as PQ node,which makes the traditional power flow algorithms inapplicable. An improved distribution network power flow algorithm with node incidence matrix squaring is presented,which only modifies the node incidence matrix according to the path from original root node to new root node when the operating mode of distribution network changes,renumbering is not necessary. The reactive initial value decided by the traditional algorithm for the connecting point of PV-type DG is often far from the real value. An algorithm to determine the reactive initial value according to the location of DG is proposed,which apportions the load reactive power between the root node and the DG. An example proves the calculated reactive initial value is near the real value and the convergence speed is improved.

Information modeling and communication of SF_6 circuit breaker on-line monitoring system based on IEC61850

Abstract: According to the characteristics of SF6 circuit breaker state on-line monitoring, it is proposed to fully use the logical node GGIO (Generic Input / Output) of IEC61850 in the modeling of intelligent electronic devices. The on-line monitoring data of circuit breaker state is transferred by GOOSE (Generic Object Oriented Substation Event) message with time delay less than 4 ms,which applies publish / subscribe model. Its scheduling and communications mechanism are introduced. VxWorks, an operating system by excellent real-time performance is selected and the model communication program is written by VC++ in its Tornado compiler debugging environment. The main functions and flowcharts of analysis program are given.

Motor mechanical fault diagnosis based on wavelet packet,Shannon entropy,SVM and GA

Abstract: A motor mechanical fault diagnosis method,WPSSG,is proposed based on wavelet packet,Shannon entropy,SVM(Support Vector Machine) and GA(Genetic Algorithm).Wavelet packet decomposition and strong fault-tolerant Shannon entropy are used to compute the characteristic vectors of vibration signals,which are then served as the input vectors of multi-class SVM classifier to achieve better denoising performance.GA is used to optimize the parameters of multi-class SVM when it is trained to achieve better classification capability and higher veracity.Experiment is carried out with motor mechanical fault data from Case Western Reserve University to prove its reliability and veracity.

Interior-point nonlinear algorithm with complementarity constraints for reactive-power optimization

Abstract: A nonlinear reactive-power optimization model with discrete variables and complementarity constraints is established and the corresponding interior-point nonlinear complementary algorithm is presented for power system. The discrete variables of transformer tap and capacitor bank are treated as continuous variables in reactive-power optimization calculation to quickly obtain their upper and lower bounds,which are used as the complementarity constraints of the model. The interior-point nonlinear algorithm is then used to calculate the best solution of transformer tap position and capacitor bank number,which coordinates the calculation time and precision more effectively than traditional methods. The calculative results of several test systems show that,the proposed algorithm has good convergence property and real-time performance,suitable for the on-line reactive-power optimization of large-scale power system with discrete variables.

Model and method of large scale grid fault diagnosis based on multi-agent system and information fusion technology

Abstract: Traditional fault diagnosis methods only analyze the information of protections but the information of grid features reflected by the electrical variables.A fault diagnosis model based on MAS (Multi-Agent System) and information fusion technology is proposed,which,according to the structure and characteristics of large scale power grid,integrates different fault diagnosis methods to analyze for different areas the fault information collected from data recorders,SCADA and RPMS,employs the evidence theory to perform the information fusion to obtain the divisional fault diagnosis conclusions,and identifies finally the faulty components by the global fault diagnosis.The simulation indicates the proposed model and method is accurate and effective.

Faulty section detection algorithm for distribution system with multi micro-grids

Abstract: A master-slave regional pilot protection system is proposed for distribution system with multi micro-grids.The relationship matrix is defined based on the network configuration and its operating mode and the fault information matrix is defined based on the direction information of faults at different points of protected line.The faulty section can be detected quickly and reliably by simple multiplication calculation of two matrixes.The sensitivity and reliability are almost immune to the capacity of micro-grid and its connection position.The influence of incomplete fault information on faulty section detection algorithm is analyzed and the error tolerance of the algorithm is studied.

Fuzzy-immune MPPT control of PV generation system under partial shade condition

Abstract: PV generation system is partially shaded at times in actual operation,which makes the PV output characteristics more complicated.Aiming at its nonlinearity,uncertainty and multi-peak,fuzzy logic is applied to track the actual maximum power point of system.The conventional fuzzy logic controller is further improved to realize the fuzzy perturbative tracking under partial shade condition and the artificial immunity theory is used to enhance the response speed and robustness.The simulative results show that,the proposed method has a better dynamic performance than that of the traditional PO method.

Comparison of fiber current differential protection synchronization schemes for smart substation

Abstract: As the current sampling and processing are implemented in two equipments with CPU in smart substation,three synchronization schemes based on sampling time adjustment are proposed for the fiber current differential protection:synchronous source,phase-locked loop and interpolation synch.Each is analyzed in the applicable occasions,implementation principles,advantages and disadvantages.The conclusion is that,the synchronous source has limited applications because of its dependency on synchronizer,the phase-locked loop is suitable for sampling value networking because of its immunity from network disturbance,and the interpolation is suitable for the point-to-point mode between merging unit and protection in smart substation.