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1.
Addressing the problem of choosing a fault line under single phase to ground of distribution network, we presented a new criterion based on analysis of the development of fault line selection and a method using wavelet packets. The feature frequency band, or the combined feature frequency bands of each line, in which the transient capacity current was concentrated was chosen for maximum energy. Based on the principle that the transient capacity current's energy of the fault line was larger than the that of normal lines, fault line selection can be carried out adaptively by contrasting the energy of the transient capacity currents of all lines in each chosen frequency band. The simulation results and spot testing data shows the proposed method can detect the fault line in distribution networks precisely and reliably. 相似文献
2.
By analyzing shortages of current MSPCA model, an on line multi variable statistical process monitoring method is proposed, which uses some concepts from online multi scale filtering and can be applied to sensor fault diagnosis. In the method, wavelet decomposition is employed to the signals using edge correction filter in a fixed length data window, and then wavelet denoising is conducted with wavelet threshold filtering. Next, an on line multi scale model is constructed for data combining wavelet transformation and adaptive PCA in the previous data window. This model avoids time waste in direct signal denoising and reduces time cost in multi scale data with conventional PCA, which eventually increases accuracy in fault diagnosis. Experiments on eight vibration signals of 6135D diesel engine under severe leak condition prove the practicability and feasibility of the proposed method. 相似文献
3.
Application of higher density wavelet transform to composite fault diagnosis of rolling bearing 
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下载免费PDF全文 Aiming at the difficulties in accurate reorganization of several weak faults currently, a composite fault diagnosis method based on higher density discrete wavelet transform and envelope spectrum is proposed. Firstly, the higher density discrete wavelet transform is used to decompose acquired vibration signals of rolling bearings. Then, the single-subband reconstruction is performed on the wavelet coefficients and scaling coefficients at each scale in order to solve frequency aliasing. Finally, the envelope spectra of all subband signals are calculated, and all faults can be recognized according to the characteristic frequencies of the typical faults. The proposed method is applied to the diagnosis of the rolling bearings with composite faults, and is compared with other common fault diagnosis method. The results show that the proposed method can be effectively used for the early composite fault diagnosis of rolling bearings. 相似文献
4.
The voltage instability of power system often occurs when the active power on one or more weak branches exceeds its transfer capability. A preventive control model for static voltage stability is proposed using the active power transfer capability of weak branches as static voltage stability constraints. A local line based voltage stability index is used to determine the critical contingencies, weak branches and transfer capability of each weak branch. A static security analysis method, which is based on DC power flow equations, is used to establish the non linear active power flow expressions on weak branches following each critical contingency. The active power constraints on weak branches can be obtained from the active power flow expressions and transfer capabilities of weak branches. A quadratic optimal model for preventive control including the proposed active power constraints on weak branches is presented. The simulation results for IEEEE14 bus system and IEEE118 bus system demonstrate the correctness and effectiveness of the proposed preventive control model. 相似文献
5.
In order to solve the incipient fault diagnose problem of the transmission system, a networking condition monitoring and failure diagnosis system based on B/S and C/S hybrid architecture for wind turbine transmission system is designed in the paper. Firstly, the paper analyzes the demands of condition monitoring and fault diagnosis system for wind turbine transmission system, and designs its overall framework and function modules. Then, combining with the data acquisition equipment, by the .NET and SQL Server platform, the paper designs condition monitoring and failure diagnosis system for wind turbine transmission system, which includes the functions of networking data acquisition, remote condition monitoring, signal analysis, fault diagnosis and database as well. The system has been successfully applied to a condition monitoring and fault diagnosis of wind turbine transmission system. 相似文献
6.
The accuracy of modal parameters identification has the influence on the quality of dynamic characteristics analysis of mechanical structure directly. And the precision of the frequency response function estimation has the great influence on the accuracy of modal parameters identification. In the engineering the frequency response function can be estimated by the average power spectrum and cross-power spectrum with the hel Pof FFT. As the result of limited frequency resolution in the course of FFT and the noise, the accuracy of modal parameters identification is influenced by the frequency response function estimation. This paper has put forward a least-square-based optimization of frequency response function estimation in modal parameters identification. According to the optimized frequency response function, the peak value can be searched to identify the damped natural frequencies and damping ratio directly. An experiment has been made to validate the proposed method. The result indicates that the damped natural frequencies and damping ratio identified by the optimized frequency response function are closer to the true results than which without the optimized frequency response function. So the accuracy of modal parameters identification can be improved by adopting the proposed method. 相似文献
7.
Transient analysis of transmission line has recently been received more attention because operating speeds in high-speed digital electronics are increasing. Transmission line equations are hyperbolic partial differential equations, firstly this paper deduces how to change transmission line equations into quasilinear differential equations , thus the transmission line equation numerical result is gotten by computing the differential formation of quasilinear differential equations. The constraint of voltage and current is be considered and lumped equivalent circuit mode at boundary network collaborated at the same time in finding boundary conditions. Finally the paper computes transient response of transmission line with two typical boundary conditions. Numerical result shows that this approach is an effective way. It is explicit algorithm with less CPU consumption which can get time field response directly. The agree-upon effective way does be frequency field method, however it could not get time response unless the numerical inverse laplace transformation (NILT) be introduced. Thus this approach is more effective than FFT algorithm. 相似文献
8.
We present an aeroelastic model design and method creation based on the case of an ±800 kV ultra high voltage (UHV) power transmission line from Xiang Jiaba to Shanghai, P. R. Chin, Both the centralized and discreted stiffness modeling methods are unsuitable for tower aeroelastic modeling. Taking these stiffness and aerodynamic characteristics into account, we introduce a new method to create an aeroelastic model that includes a semi rigid model segment and U shaped springs. Because the span of this transmission line is too long to fit within the wind tunnel in the same proportions as the tower, the proportions of the line model is condensed further. Aeroelastic test requirements can be satisfied by comparing theoretical analysis and actual measurements of the system model dynamics. 相似文献
9.
Photoacoustic spectroscopy (PAS) is a highly sensitive gas analyzing method without the shortcoming of gas consumption, which can be used in transformer oil trace gases dissolved in on line monitoring. The photoacoustic signal is detected with a microphone, which is the only feature in gas concentration analysis. A portable and tunable experimental setup has been developed based on the photoacoustic spectroscopy fundamental. Through the photoacoustic signal stimulate mechanism analysis, this paper thoroughly discusses the influences of gas pressure, temperature, laser power, gas concentration, background gas, chopped frequency and the resonant frequency drift on the gas photoacoustic signal. The theoretical and experimental results supply reference and technical support for further improvements in oil gas photoacoustic spectroscopy of on-line monitoring system. 相似文献
10.
Analysis of the distorted scaling factor in wind tunnel modeling of power transmission line system
Because of the limitation of the model making and the existing wind tunnel’s size, it is difficult to keep the line and tower in the same scaling factor in developing the aeroelastic model of the power transmission lines system, and a distorted scaling factor is needed in span length of the lines. With the instance of a 1 000 kV two circuit power transmission lines, the finite element analysis under the along wind load in time history is conducted with keeping the tower in the same and the line scaling factor being 1, 0.5 and 0.25 respectively. The results show that the response of the power transmission lines systems keep in the same, and then the wind induced vibration of the distorted model in the wind tunnel test can actually reflect the response of the power transmission lines system under the wind load. 相似文献
11.
The tremendous power flow may be transfered when two-phase short line is shut down, which may result in unstable state of the system and large loss of electric power. A novel line fault current controller (LFCC) and control method for the fault current of the two-phase short are presented. LFCC, emdedded at the line terminal, is composed of a series-connection transformer, a shunt-connection transformer,2 controllable inductors and on-line taps and is equivalent to the series of the insertion voltage and the insertion inductor when it works. The insertion voltage at the sending terminal(receiving terminal) is controlled to lead (lag)the fault source voltage by 2π/3 by adjusting on-line taps states. Because the insertion voltage amplitude and the insertion inductance can be controlled independently, the fault current gets zero and the current through the fault line reaches the normal current by the appropriate control of the insertion voltage amplitudes and the insertion inductances. Therefore, the fault line keeps the operation and the current through the line during the two-phase short existing equals that in normal operation, which improves the supply reliability. In addition, the corresponding control strategy for two phase short current is proposed. The experiment results show that the proposed LFCC is able to control the fault current through the line to reach corresponding normal current. The proposed control method suited for the proposed LFCC for the two phase short current is verified with the simulation results. 相似文献
12.
To solve the problem that the existing method of extracting fault components is easily affected by power system swing,a new methed has been proposed in this paper,which can be used in high speed protection of transmission lines. This proped method ean greatly decrease unbal-ance outputs under power swing condilions without frequency tracking circuits,therefore it can make the protection using fault compnents operate correctly. 相似文献
13.
A digital monitoring and fault diagnosing system for ship power plant based on fuzzy neural network and dempster shafer(D S) evidence theory is developed. The system includes data acquisition part, software control part and analysis part, which can monitor the main propulsion device, diesel generator and auxiliaries. The main propulsion device can be real time dynamicly monitored by acquiring cylinder pressure and instantaneous angular speed. Using thermodynamic parameters and instantaneous angular speed, two sub fuzzy neural networks are parallel constructed. The fault of main propulsion device is judged by data fusing algorithm of D S evidence theory, and finally the result of fault diagnosis can be obtained. Test shows that the system’s real time performance and measurement accuracy can meet requirements, and the fusion method of fuzzy neural network according to D S evidence theory has relatively high reliability. 相似文献
14.
GONG Xian sheng 《保鲜与加工》1999,(3):15-23
A method which is used for calculating steady vibration response of shipping propulsion shafting connecting with a coupling with nonlinear hysteresis characteristics are studied. On condition that the nonlinear dynamic stiffness and hysteresis damping of the coupling be considered, on the basis of GLM(Galerki Levenberg Marquard) method, a method called SSGILM(Separate System Galerkin and Improved Levenberg-Marquardt)to be used for calculating steady vibration response of propulsion shafting with local nonlinear dynamic stiffness and hysteresis damping, is proposed. A simple example is given out and the analyses show that it is effective to calculate steady vibration response of the shafting with local nonlinear dynamic stiffness and hysteresis damping by SSGILM method. From initial response values given arbitrarily, the automatic search algorithm in SSGILM method can converge the given initial response values to the response values accorded with required accuracy quickly; nonlinear dynamic stiffness and hysteresis damping of the coupling have different effect on vibration response of the shafting at different range of frequency. At the area of close nature frequency of the shafting ,displacement amplitude of the shafting is bigger. Beyond the range, the characteristics of the coupling have restraint effect on vibration of the shafting. 相似文献
15.
Multiplex analytical method for metal three dimensional flow of heavy rail rolling by universal mill
With the monitoring data of groundwater level of some reservoir slope, the nonlinear combined model was established on the basis of establishing the time series method and speed analysis method. Upon the comparison, it was found that the precision of non linear combined model was higher than that of single model. It was an effective prediction method for groundwater level of reservoir slope and could be employed for stability prediction of reservoir slope. 相似文献
16.
The turbogenerator vibration faults have the character of variety. Many faults often occur synchronously. This paper introduces a diagnosing model based on parsimonious covering theory and probability. A model for turtogenerator's fault diagnosis is proposed. The availability of this method is proved by two fault diagnosis examples of turbogenerator. The results show that the model proposed can be used for multi_fault diagnosis together. It may make up shortage for some of expert systems and neural networks in some aspect. From the practice,this model has higher reliability and practicability. 相似文献
17.
CAI Jing zhi 《保鲜与加工》2003,(4):93-95
With the development and application of information and internet and virtual instrument technology ,the virtual globular company based on internet arises .To study remote state monitoring, remote fault detection and diagnosis about large scale, complicated and integrative equipment become very important. In the whole fault diagnosis system , the detecting ,data acquisition is original ,processing; transform and extracting features with the signal detected is a key factor. The theories and methods used in mechanical fault diagnosis is stated. The application of signal process and its feature extracting methods is introduced which are time domain, frequency domain and time frequency domain analysis, in state monitoring and fault diagnosis with its signal analysis. The processing method of random time variant special signal is given also. 相似文献
18.
This paper presents a method which can accurately calculate the fault voltages and currents of the transposed and untransposed transmission lines.It can be applied to the simulation of protection relay analysis and fault location and so on.The principle of method is clear,the computational precision is high and usage is simple. 相似文献
19.
On the basis of partial decomposition in frequency domain with harmonic wavelet package method and Hilbert demodulation, the demodulation based on harmonic wavelet package transform is introduced. The Fourier spectra analysis is carried out after preprocessing, and the depth of decomposition and frequency band are determined by the analysis of frequency band distribution and the theoretic computation of gear box characteristic frequency. Then with FFT and IFFT the corresponding meshing component is extracted. Finally, the modulation information is extracted via Hilbert envelop analysis approach. With the proposed method, wear and notch faulty gearbox are tested and analyzed by experiment, respectively. The results prove that this method can locate gearbox fault precisely and provide corresponding basis for judging fault cause and degree. 相似文献
20.
Analyze the Present Status in the Calculation Methods of Lightning Protection Performance for Transmission Line 总被引：1，自引：0，他引：1
Lightning is the main reason that endangers transmission line working safety and reliabilty today. The theory and characteristic of methods that not only estimate the lightning performance for back strike such as standard method, traveling wave method, Monte Carlo technique, treeing fault method, EMTP and so on but also for the shielding failure such as standard method, EGM, leader progression model and so on are summarized. The criterion of flashover for insulators is referred simply, furthermore, it gives the opinion that the development of research for the future. 相似文献