Computation method of magnetic field inverse problem on grounding grids fault diagnosis

Grounding grids are the guarantee of substation running safety. The fault of grounding grids is a threat to people and equipment in substations. A method to diagnose the fault of grounding grids based on magnetic field inverse problem. The inverse problem of magnetic field is established by injecting and extracting a low frequency current. The morbid of inverse problem is solved through regularization and Newton iteration method to obtain the distribution of the mesh currents. The approximate distribution of the magnetic field is calculated to diagnose the fault of the grounding grid. A 4×4 substation grounding grids is taken as an example. By comparison of the forward problem result, the error is under 3%, so the prposed method of inverse problem is verified. The selection of measurement point is discussed, and 40% of the number of meshes is accounted to approximate the real distribution of the magnetic field on the grounding grids.     

Calculating the Hollowing-center Grounding Device Resistance Based on the Surface Charge Simulation Method

An equivalent model for hollowing-center grounding device is proposed, the hollowing-center grounding device resistance is calculated with the surface charge simulation method and the computer programme is programmed based on this model. The accuracy of the model and method is validated by experimentation.     

Analysis on the method of selecting nodes on the erosion diagnosisof grounding grid

The number of underdetermined equation, which is limited by the grounding down lines, reduces the grounding grid corrosion diagnostic precision. Based on the grounding grid fault diagnosis method and sensitivity analysis, the value of slip resistance change on the impact of the port resistance in several cases, such as small span, large span and edge, center and symmetrical cross line of the grounding grid, is analyzed. A new method which is used to select the node pairs to calculate the corrosion situation of grounding grid is presented. Based on this method, the simulation analysis and field test has been done. The experimental results show that this method could improve the accuracy and efficiency of grounding grid fault diagnosis.     

Theoretical Analysis for the Performance of HVDC Grounds Electrodes and the Mathematical Modal

The performance of HVDC ground electrodes is analyzed in detail.On the basis of electromagnetic field theories and its assumptions,the mathematical model is built,the ground resistance,the distribution of potential and temperature are computed with the current field distributions of HVDC ground electrodes.     

Simulation analysis on stimulation patterns of three-dimension electrical impedance tomography

To solve the lack of information and the error in forward and inverse problem caused by the approximation of actual three-dimensional field from two-dimensional field in electrical impedance tomography (EIT), this article presents a new EIT system. This system improves one-dimensional electrode array to two-dimensional array, and extends the solution domain to the entire three-dimensional field in order to increase the information quantity and eliminate the model error. Based on several current stimulation patterns in EIT which might yield the best sensitiveness for 3-D field, we calculate the forward problem by finite element method and the distinguishability and surface projection image method. The results show that the back electrode pattern has obvious advantages in detecting depth and precision, and has convenience in clinical application. The conclusion of this article can provide reference for the study of 3-D EIT.     

Effect of Cobalt Ion Implantation on Behavior of Ni(OH)_2/NiOOH Electrode

Clectrochemial reaction occurred on Ni(OH)2/NiOOH electrode was studied with electrochemical method and ellipsometry with wavelength sweep.Cobalt was implanted intosurface of nickel with fonim plantation technology to improve charge efficiency of the electrode. With fitting ellipemetric experimental data,transformation model of the surface film was obtainedduring charge and discharge. Implantation of cobalt did not affect the model,but made charge effi-ciency be increased.     

Another Method of Deducing Maxwell Equations

It is well-known that the theoretical basis of macroscopic electrodynamics is Maxwell equations,include which Coulomb law, Biot-Savant law, Faraday law of electromagnetic induction and the hypothesis of induced electric field and displacement current. When the distribution of electric charge and electric current varies with time, if given Coulomb law, Biot-Savant law, Faraday law of electromagnetic,and the hypothesis of induced electric field, through the vector analysis, Maxwell Equations are given without the hypothesis of displacement current.     

Analysis of fast optimization algorithm for inverse detecting faulty insulators

In order to improve the computational efficiency of the insulator electric field inverse problem, the fast multi-pole method has been introduced to the traditional simulation charge method. Tikhonov regularization is used to process the ill-posed characteristic of inverse problem solution caused by the interference. Newton method is used to search the optimum solution, and then the actual field source parameters of insulators and the practical voltage distribution on the surface of the insulators can be obtained. The fast optimization algorithm has been verified in point charge model. And 110 kV insulator string is carried out to demonstrate that the fast optimization algorithm is much faster and more efficient than traditional method.     

Calculation of lumped parameter of two-port network forvolume conduction energy transfer

Skin electrode unit is a channel through which energy can be transferred to the implanted device by volume conduction. The unit can be equivalent to lumped circuit, but so far there are no appropriate calculation methods of these circuit parameters, so variable load method based on field-circuit coupled is proposed. A skin electrode unit field circuit coupled model is established to obtain the relationship of the network parameters between voltage and current at electrode port, and the amplitude and phase of the power signal is extracted by the use of all phase FFT spectrum analysis. On this basis, equivalent circuit impedance parameters of the skin electrode unit under various conditions are obtained by the application of variable load method and the validity of the method is verified. As a result, the equivalent circuit impedance parameters obtained in this way can be used for the circuit analysis and optimization of the volume conduction energy transfer system.     

Optimization algorithm for forward problem with electric fields of defective insulator

The defective insulator can be detected by measuring electric field, however, the electric field calculation accuracy of the insulator strings is low. Charge simulation method (CSM), which is optimized by genetic algorithm (GA), is adopted to calculate high voltage electrostatic field. The optimal method principle and feasibility analysis is given. The objective function and optimization model of electric field distribution around insulator strings are constructed and analyzed. The results of calculation and analysis demonstrate that adopting the potential of check points near insulator strings as objective function and using GA to optimize the charge of simulation charge, better performance can be achieved for improving ability of global optimization, calculating precision, searching speed, simulating precision of CSM and accuracy of diagnosing defective insulator in the insulator strings.     

Refined Probabilistic Model of Resistance of RC Eccentric Compression Members

The probabilistic model of resistance in the current unified standard for reliability design is imprecise for RC members subjected to eccentric compression. The reason is that it lacks full considerations of influences of varying eccentricities. An improved probabilistic model of resistance with different eccentricities and reinforcement ratios is obtained by using the Monte Carlo sampling method and the current probabilistic models of all resistant factors. The results indicate that it is accurate to fit the probabilistic distribution of resistance with normal distribution. Given that, the applicability of the improved model is analyzed for reliability analysis of RC members subjected to eccentric compression with random eccentricities. It shows that when the design value of eccentricity is close to or larger than the eccentricity producing balanced failure, there would be large errors in reliability analysis if the probabilistic model of resistance given in the current reliability unified standard is used. However, it is accurate when using the proposed probabilistic model. The results also show that the design of RC members subjected to large eccentric compression is unsafe based on the current reliability unified standard because it lacks full considerations of effects that the resistance decreases as eccentricity increases.     

Harmonic Analysis and Suppression of High-frequency Welding Devices

This paper analyzes the structure and line current waveform of 3-phase AC voltage regulation circuit. As an application of 3-phase AC voltage regulation circuit, a high-frequency welding device's simulation model and harmonic analysis of line current are presented. Results of simulation are compared to field measurements. The two are in a good agreement, so this simulation model is correct. Two single-tuning filters and one second-order HPF are designed according to the device's harmonic condition. Simulation results of the circuit with filters indicate decrease of the harmonics in current of power supply, and the waveform is close to sinusoidal wave, which prove correctness of the solution to harmonics pollution.     

雷电引起接触电压、跨步电压导致生物伤害的损害概率计算方法探析

为了提高人员生命损失风险计算的针对性、准确性,为人工接地装置安全布设提出建设性的指导意见,通过对人工接地装置泄流时接触电压、跨步电压的计算方法的分析,确定了人工接地体泄流时接触电压、跨步电压导致人身伤亡的损害概率的定量计算方法。计算时,通过对接触电压、跨步电压计算值与人体耐受接触电压、跨步电压阈值的比较分析,确定能达到该阈值的最小雷电流幅值,再通过对项目所在位置雷电活动特征的分析,确定可能超过灾害阈值对应的雷电流幅值,即可能产生风险的雷电流所占的频率,认为该频率即为接触电压、跨步电压导致生物伤害的损害概率。对人工接地装置接触电压、跨步电压的计算以垂直接地极为例,同时考虑了冲击电流较工频电流对计算方法的影响。     

Surface Charge Distribution and Tip Electric Field about Carbon Nanotubes

Carbon nanotubes(CNTs) have some special physic properties which may own important technical values. We studied the electric characteristics of metallic carbon nanotubes including potential distribution, surface charge distribution and tip electric field based on electromagnetic theory. Our results show that the relative values of tip charge densities of short CNTs are bigger and so are the absolute values for long CNTs. We also find the electric field at the tips of metallic nanotubes is much bigger than external electric field. This is helpful for exploring theoretical problems about CNTs' field emission.     

Numerical Analysis of Diffusion Characteristic in the Proton Exchange Membrane Fuel Cell

A two-dimension,steady-state,multi-component transport model is presented to investigate the cathode performance of a proton exchange membrane fuel cell with an interdigitated gas distributor.Darcy law is used to describe the flow in the porous media.Subsequently,the model is applied to predict the pressure,velocity and mass fraction distributions in the electrode and explore the effect of the change of differential pressure between the inlet and the outlet,electrode thickness and rib width on the performance of fuel cell.The results show that: current density creases with the higher differential pressure between the inlet and outlet,but the increment is diminishing;electrode thickness has an optimum value which depends on the electrode morphology and the gas distributor design parameters;using narrower electrode rib can improve the performance of fuel cell.     

Comprehensive Intelligent Wire-selection of Neural-based Small Current Grounding System

This paper centers on the study of intelligentized fault lineselection when the small current grounding electric system is grounded in single-phase. Based on the known theories and methods of groundingline-selection, we propose a comprehensive neural-based intelligentized processing plan, which offers a new approach to improving accuracy rate of fault line selection andevaluating various arithmeticfor grounding protection in practice.     

Analysis on Dredger Fill Electrical Response Under Additive Electrical Field

With the purpose of the study on change rule of internal charge in soil specimens under differing circumstances, dredger fill, which was collected from Guangxi Beibu Gulf Economic Zone, was studied in various parameters, including the absence/presence of the applied DC electric field, different levels of field strength, soil water content, soil compactness, and degree of desalination. Moreover, through tentatively simulating the electrical response between thundercloud and earth mass, the triggered lightning mechanism of rock soil mass was explored. The results show that both additive electrical field and atmospheric electric field had influence over charge variation of soil, the impact of which would become more significant with the increasing field strength. Higher soil water content and lower degree of desalination could enhance the charge variation and conductivity of soil, whilst this action effect would remain stable when soil water content reached a certain degree. Although soil compactness make some effect for the charge distribution, its regularity is undefined so far.     

Theoretical analysis on the protection properties against electric shock of low voltage DC distribution system with different grounding types

The low voltage direct current(LVDC)distribution system has great potential and advantage to be applied to conventional areas, such as residential house, due to its characteristics of energy conservation and being eco-friendly, but there is no existing standard specifications to guide its application in practice to ensure the electrical safety of this system. The protection against electric shock is a key indicator of electric safety, but the effect of electric shocks on AC and DC are different. Refer to the international standard IEC60479-1 and analytical method in AC system, the protection against electric shock between DC 750, 400, 300, 220 V and AC 220 V systems are compared and analyzed based on ideal DC source model. It demonstrates that the negative grounded TT & TN DC distribution system has significant advantages over the traditional AC system, and the safety voltages are given, which could be a reference to develop the normative guidance for the application of LVDC in practical application.     

An Attentive Problem of 35 kV Power Lines in Mountain Area on Protecting Against

To counteract capacitive current and resume power system, the neutral point of 35 kV power system at the mountainous area is grounding through the arc winding widely. In fact, there is great difficult in selecting the arc winding to satisfy the requirement of system. In a 35 kV power system which neutral point is grounding through the arc winding, the capacitance current are measured in site when a single-phase is grounding. From the measure data, the imbalance of three-phase voltage whether the arc winding exist or not and the operating situation of arc winding are discussed, and bring forward an attentive problem about operation of arc winding and decrease of lightning outage rates.     

CCD radiation temperature measurement method for hot continuous casting billet surface

According to the present research status and existing problems of hot continuous billet surface temperature non contact measurement technology, a real time temperature measurement model, which combines two-color(R,G) and monochrome (B) of surface radiation image, is established. The surface image is collected through tricolor charge coupled device (CCD) sensor, at the same time, the temperature dynamic response range of CCD can be improved by controlling integrated time and setting different apertures. Through computer image process technology, multi-point temperature can be measured simultaneously, and 2-D temperature field distribution on continuous casting billet surface can be realized. It is be proved by theory and application that the model and method can provide a theory and technology support for realizing surface temperature field on-line measurement for continuous casting billet.