Characteristic analysis of partial discharge in high voltage XLPE cable accessories

Four physical models of typical internal insulation defects in 110 kV cable joints are designed and a test platform for partial discharge (PD) research on cable accessories also is constructed. Based on the models, plenty of PD data are obtained for vario     

Partial Discharge in Oil-paper Insulation of Transformer

Based on the analysis of defect in oil-paper insulation of transformer, 5 corresponding PD models were made to simulate the actual defects existed in transformers. Aging experiment was carried out at different temperature and test voltage. The developing process of different types of PD was studied and the influence of temperature and voltage on PD in oil-paper insulation, were analyzed. Gray images show differences for different typrs of PD or one type of PD at different precedures. Gray images can be used to recognize PD patterns and discharge stage. The research resalts coutribute for further research on PD pattern recognition and insulation aging of transformer.     

Characteristics of UHF partial discharge signal waveforms of typical insulated defects in GIS

In order to analyze the discharge features of different insulation defects in various experimental conditions, according to characteristics of partial discharge (PD) from the insulation defects in gas insulated switchgear (GIS)) and using ultra high frequency (UHF) method, a lot of PD experiments are carried out based on the designed four typical physical models of insulation defects of GIS in the simulation device, and the real samples of UHF PD waveforms are recorded. The features of UHF PD waveforms in the different situations are discussed and analyzed in detail, which include different sizes or positions of the physical models or under the different voltages and so on. The results show that in low voltage, regardless of types of UHF electromagnetic wave excited by PD sources, the shapes of PD waveform changed little before the changes of waveform. The remaining time is about several nanoseconds.     

Theoretical Analysis of Static Performance of Super Span Suspension Bridge with CFRP Cable

Equilibrium equation and compatibility equation are deduced to get the cable force equation and cable displacement control equation. Then the expression of characteristic parameter λ 2 in cable force equation is deduced. Meanwhile, the influence on the increment of cable force and displacement caused by λ 2 and load ratio P is analyzed. On this basis, taking 3 000 m span suspension bridge as a calculating example, the characteristics of the increment of cable force and cable displacement under symmetrical and asymmetrical load are studied. In this case, two different conditions are considered. One takes the elastic elongation into consideration, but the other does not. At last, compared with the steel cable, the influence on the parameter in cable force equation and displacement control equation caused by span is analyzed. The influence of the static performance of suspension bridge by parameter changing is analyzed as well. The substantive characteristics of the static performance of super span CFRP suspension bridge are cleared and the superiority and characteristics of CFRP cable structure are demonstrated in theory.     

A Review of Concrete Damage Constitutive Models

The existing constitutive models of concrete are mainly based on the framework of the classic elastic -plastic models which are rigorous on mathematics, but not coordinated with the failure mechanism of concrete. Researchers of different countries proposed various kinds of damage constitutive models based on the irreversible thermodynamics theory to describe the damage behavior of concrete. This paper presents a review of different models for concrete,analyzes the characteristics of each representative model and studies the scope of their application. On the basis of the review of existing concrete damage models, some new methods can be provided for further research on damage constitutive models.     

Comparision of Theoritical Solutions and Ultimate Span-Length between FRP Cables and Steel Cables

As the self weight of cable affects mechanical behavior obviously with the inerease of span length.FRP (fiber reinforced polymer) cable that has the lighter weight than the conventional cables has advantage for long span structures.The analysis of single cable is the fundamental theory for the design of cable structures.Based on different considerations of gravity loads.the solutions of the single cable on gravity loads have three sets of solutions: parabola solution.catenary solution and elastic catenary solution.And the equations for the three sets of solutions are derived by taking the end tension force of cable as the control parameter.The comparison between FRP cables and steel cables is conducted by elastic catenary solution.and the results show that the lager span structure can be realized by FRP cables.The precision for the parabola solution and catenary solution is compared for stay cables and horizontal cables.and the proper ranges of both approximate methods are proposed.Based on the above methods.the ultimate span length of FRP cable and steel cable are analyzed.It is concluded that the ultimate span of FRP cable is 4.4 times larger than that of steel cable.     

Experimental research on the slipping performance of cable-strut joints

Based on an actual project of a suspen-dome steel roof under construction, the constraint performance of cable-strut joint of a suspen-dome is studied precisely. Experiments of a full-scale cable-strut joint are conducted on and both the slipping performance and the failure mode of the joint are obtained. The concept of slipping force density is proposed to describe the slipping performance of the joint. The static friction factor is also gained in the test and the test values are compared with analytical ones. In comparison with the smooth clamping groove, the ribbed clamping groove is proposed against the deficiency of clamping strength of the joint after the cable being tensioned. The experimental and analytical results demonstrated that 10% prestress loss occurs in seal sleeve and socket ear, so that pre-stretching is recommended as compensation. In the experiment, primary joint fails with pulling out of the cable and damage of the out layer PE. The maximum slipping force for primary joint is 150 kN with the slipping force density of 18.3 kN/mm. The measured friction factor is 0.24, which agrees well with the FEM results. The maximum slipping force for the ribbed joint is 240 kN,and the measured slipping force density is 26 kN/mm, which increase, up to 42% compared with that of primary joint. It is indicated that the ribbed damping groove can fasten the cable more efficiently, and improve the sliding-resistance performance of the cable-strut joint. The research provides references for the application of this joint.     

Trapping characteristics of low density polyethylene under DC ageing by space charge

Space charge in insulation material of high voltage direct current cable is closely linked with the ageing degree of the materials,and it is an interesting topic if one can find some characteristics to indicate the ageing of the material from the space charge measurement. In this paper,the effects of ageing on space charge characteristics of low density polyethylene (LDPE) are investigated by the pulsed electro-acoustic (PEA) method. A space charge trapping model is proposed base on distribution of discrete traps,and the characteristic parameters in the model including trap depth and trap density are calculated. The results show that the relatively shallow traps in the samples transform to the relatively deep traps as the degree of electrical ageing increases. Furthermore,the relationships between ageing degrees and trap depth and trap density are obtained. The information of the trapping parameters in our model provides a good reference for diagnosing the ageing degree of polymeric materials.     

Free vibration characteristic analysis of the elastic liquid-storage tanks based on the bending shearing model

Liquid-storage tanks, mostly used to reserve rinsing, sewerage, petroleum and chemistry liquid, are broadly applied in such industry corporations as water-supply and drainage industry, sewerage-disposal industry, petroleum industry, chemistry industry and so on. For the sake of computing preferably earthquake responding of these structures, the characteristics of their free vibration, like frequency of free vibration and corresponding oscillation-mode, have to be known beforehand. Therefore, for the liquid-storage tanks without liquid, the equations about oscillation-mode and frequency based on bending-shearing model are deduced, and at the same time, the calculation tables and chart of former three oscillation-modes are presented by using MATLAB program, and free vibration characteristics using different deformation theory in different heights are analyzed. The correctness of the result is proved by calculation example, and a theory base is provided for analyzing subsequent free vibration and earthquake responding of this type of structure.     

Numerical analysis on the thermal performance of several kinds of composite wall construction

According to climatic characteristics of the hot summer and cold winter zone, P. R. China and considering the different forms of interior and exterior insulation, different thickness of insulation, different materials of insulation and different forms of the main wall, this paper developed a physical model and a mathematic model, calculated the characteristics of materials and wall construction. It used the software Fluent to analyze thermal performance of different types of walls, to compare the interior and exterior surface temperature. The results of simulation show that under the condition of the same continuous temperature-wave, there are basically irrelative between the external surface average temperature and wall constructions. Compared among those construction with the same index of thermal inertia and heat transmission coefficient, but the different insulation-form, it shows that the exterior insulation has more attenuation and longer delay time than interior insulation ,and the interior surface has less fluctuations of temperature, stronger resistance against wave changes in outdoor temperature and better thermal stability. Under the same main wall material with different insulation materials, it shows that the heat transfer coefficient and thermal inertia can’t be used to comprehensively value the effect of thermal insulation, and the materials with more temperature attenuation have better energy-saving materials performance.     

Fault check & safeguard system of optical cable for communication based on GIS

Once fault occurs on the optical cable, it will seriously impair communication. In order to solve the terrible result caused by faults, the system implements the management of the spatial database of the optical cable and the information along it and location fault spots with celerity and legitimacy, according to the spatial and environmental characteristics on geographic distribution of the optical cable network and based on GIS, as it displays the multimedia information around the fault spot, such as landform and physiognomy. Combining the buffer with path analysis function of GIS, the system searches for the optimum path to the fault spot on the optical cable, and also gives emergency schemes to dispose the fault. This application has gained a satisfactory result for effectively managing communication optical cable resources, shortening the repair time, and diminishing the loss caused by faults.     

Reynolds Number Effect on Wind-induced Vibration of Stay-cables

In order to analyze the large amplitude vibration mechanism of cables based on Reynolds number effect, wind forces measurement and free vibration tests were carried out on cable models with/without artificial water rivulet. In the tests, the cable models without artificial water rivulet were in different surface roughness and those with artificial water rivulet attached were in smooth surface, and artificial water rivulet was attached in different positions respectively. Wind force coefficients, Den Hartog galloping coefficients and free vibration amplitudes were obtained. It is shown that in critical Reynolds number range, there is the possibility that the special wind force coefficient characteristics and flow pattern induce vibration, and this is the possible mechanism for dry cable galloping. The roughness of cable surface can change the intensity of critical Reynolds number effect and the range of critical Reynolds number. The existence of water rivulet can change the critical Reynolds number effect. For some water rivulet positions, in certain Reynolds number range, dCF/dα＜0, vibration happens, which agrees with the Den Hartog galloping criterion. In high Reynolds number range, besides Den Hartog galloping, vibrations are relevant to significant decrease of wind force coefficients and unstable flow pattern.     

Analysis on steady-state mathematical models and operating characteristics of brushless doubly-fed machine

To further study the steady-state characteristics of brushless doubly-fed machine(BDFM) with squirrel-rotor,the basic equations are given according to the coupling circuits of BDFM. And then,the mathematical models of BDFM current,active power,reactive power,electromagnetic torque and power factor are analyzed and derived respectively. Furthermore,the characteristics of torque-angle,torque-frequency,power-angle,reactive power,power factor and V-shaped curve of BDFM are obtained respectively by MATLAB simulation of a prototype. The energy conversion of BDFM is analyzed by the proposed mathematical models at the same time. The results show that all the steady-state characteristics of BDFM can be expressed as the functions of the control windings voltage,frequency and the power angle. The proposed model simplifies the analysis of the steady-state characteristics of BDFM and provides a theoretical foundation for the further study on operating stability and control strategy of BDFM.     

Application of dynamic time warping algorithm to partial discharge pattern recognition

This study uses the data sequences of apparent charge versus applied voltage （ΔQ-U) in the process of stepping-up/down the voltage as the characteristic features of partial discharge (PD). Based on Dynamic time warping (DTW) algorithm, a method is introduced to realize PD pattern recognition for insulation defect models. In the training process of DTW classifier, the train and test samples are processed by vector quantization (VQ). Moreover, the original vectors are substituted by the codeword to realize data reduction, and the DTW reference templates of various PD types are constructed by the corresponding train samples. In the testing process, the average DTW distances between test samples and each reference templates are calculated based on the accumulated distances. Recognition results are obtained by the recognition rule of nearest neighbor. The new algorithm is also supported by Fast Match (FM) technique to speed up the DTW matching process. The recognition results from five PD sources and 200 samples demonstrate the high classification rates and easy expansion of the proposed DTW algorithm. FM algorithm can save 56 percent computational time and improve the classification rates.     

Impact of Main Factor on Radio Channel of LMDS System

Characteristics of radio channel play a key role in stabilization and reliability of LMCS/LMDS system at centimeter and millimeter. Rain specific attenuation has been recognized as a principal cause for impact system performance in LMDS and satellite communications systems operating in the same frequency band. In contrast to mobile communication system, multipath is not a typically problem for LMDS system, because directional antennas are used and the antennas are sufficiently high providing a line of sight propagation path between the transmitter and receiver. Moreover, the effects of buildings, foliage, and dust storms shouldn't be ignored. The impact of these factors on signal propagation and propose corresponding models is discussed. At the last,antenna height and directivity are used in the classification of statistical channel models for LMDS.     

Product ontology screening and its application in variant design

A product ontology screening method which can be used in variant design is proposed. With the support of complete ontology view of product resources, the product functional requirement and structural characteristics are converted to demand constraints, which are used to screen product ontology. For different screening hierarchies and objects, different screening rules such as pattern matching, case matching combined with manual decision and auto matching on the basis of case-based reasoning are adopted. The semi-automatic screening method with human-computer cooperation has impressive effectiveness on the improvements of the accuracy of design schemes and the flexibility and efficiency of design process. Finally, a variant design supporting system for building door and window is developed, which proves the feasibility and effectiveness of the method.     

Horizontal Slice Method for the Stability Analysis of Reinforced Slopes

Relevant national codes usually require the transmitting coefficient method to be employed for the stability analysis of slope reinforcement, in which sliding mass is usually divided into a number of vertical slices.For some support technologies, such as rock bolting and anchor cable, the intersections between the slices and the anchor bar, and the forces mobilized in the reinforcements are different from the assumptions in this method.Thus the transmitting coefficient method confronts some difficulties during practical applications, which would influence the project quality of reinforcements.A new Horizontal Slice Method was proposed based on the overseas relevant literatures to overcome these difficulties in the stability analysis of rock bolting and anchor cable slopes.     

Classification of ultra high frequency partial discharge signalsin gas insulated switchgear based on complex wavelet transform

In order to classify the ultra high frequency (UHF) partial discharge (PD) signals resulting from four types of insulation defects in gas insulated switchgear (GIS), the complex wavelet transform is applied to extract features of UHF PD signals. Five statistical parameters including mean, variance, kurtosis, skewness and energy are used to quantize the scaling coefficients of the complex wavelet transform and describe the feature subsets of UHF PD signals.A critical index J is defined to select features according to their classification performance. Using the J criterion, five optimal features are selected from sixty UHF PD features and taken as the input of radial basis function neural network. The classification results show that the information of real part and image part of complex wavelet coefficients indicates the characteristics of UHF PD singles and the recognition effect is pretty good. To use db4 complex wavelet can get the best classification performance.     

Water Supply Sources and Mode of Water Supply System for Small Towns in China

A number of problems exist in water supply to Chinese small towns. Among them, the most significant problems are the scarcity of water source and irregularity of water supply system construction. Criteria for routine water sources are established based on the analysis of present characteristics and problems of water supplying in different areas in China, recommending that water source with onsite characteristics and non-traditional features act as water supply sources or backup sources. Karst water, rainwater catchment utilization, and municipal wastewater reuse are singled out as promising ways for water supply in the future. Then different water supply systems are classified for various types of towns to employ. Finally, framework for regional water supply is advised strongly for the three types of small towns with the consideration of respective economic level. Thus, feasible, stable, effective and cost-saving water supply systems are setting up for decision making.     

Pd Pattern Recognition Based on Linear Discriminant Analysis in GIS

According to the character of PD in GIS, the authors design four kinds of GIS defection models. The GIS gray intensity images are constructed based on mass specimens gathered by the ultra - high frequency and high speeds systems, Aiming at the PD characteristics and its defections, A PCA-FDA method is put forward based on PD images. The principal component analysis is employed to condense the dimension of PD images, then the optimal sets of statistically uncorrelated discriminant vectors are extracted, and the minimum distance classifier is constructed as classifier. The identified results show that this method can effectively elevated the discrimination of the four kinds of defects in GIS PD.