非线性电阻——高能氧化锌在高压电力系统中的应用

本文介绍了氧化锌非线性电阻的伏安特性.在发电机及变压器供电网络加装高压限流熔断器和高能氧化锌非线性电阻可有效解决断路器保护的诸多不足.

高压限流熔断器组合保护装置的应用

巴江口水电站厂用电及坝区用电取自10.5 kV发电机电压母线上,但发电机电压母线的短路电流很高,且非周期分量很大,必须使用专用的发电机出口断路器,为了节省投资,电站使用了高压限流熔断器组合保护装置,既能在发生短路故障时可靠地排除短路故障、承担控制和保护的任务,价格又比较低。

Numerical Analysis of Explosion Characteristics of Vent Gas From 18650 LiFePO_(4) Batteries With Different States of Charge

The combustion and explosion characteristics of lithium-ion battery vent gas is a key factor in determining the fire hazard of lithium-ion batteries.Investigating the combustion and explosion hazards of lithium-ion batteries vent gas can provide guidance for rescue and protection in explosion accidents in energy storage stations and new energy vehicles,thereby promoting the application and development of lithium-ion batteries.Based on this understanding and combined with previous research on gas production from lithium-ion batteries,this article conducted a study on the combustion and explosion risks of vent gas from thermal runaway of 18650 LFP batteries with different states of charge(SOCs).The explosion limit of mixed gases affected by carbon dioxide inert gas is calculated through the“elimination”method,and the Chemkin-Pro software is used to numerically simulate the laminar flame speed and adiabatic flame temperature of the battery vent gas.And the concentration of free radicals and sensitivity coefficients of major elementary reactions in the system are analyzed to comprehensively evaluate the combustion explosion hazard of battery vent gas.The study found that the 100%SOC battery has the lowest explosion limit of the vent gas.The inhibitory elementary reaction sensitivity coefficient in the reaction system is lower and the concentration of free radicals is higher.Therefore,it has the maximum laminar flame speed and adiabatic flame temperature.The combustion and explosion hazard of battery vent gas increases with the increase of SOC,and the risk of explosion is the greatest and most harmful when SOC reaches 100%.However,the related hazards decrease to varying degrees with overcharging of the battery.This article provides a feasible method for analyzing the combustion mechanism of vent gas from lithium-ion batteries,revealing the impact of SOC on the hazardousness of battery vent gas.It provides references for the safety of storage and transportation of lithium-ion batteries,safety protection of energy storage stations,and the selection of related fire extinguishing agents.

Solving Navier-Stokes equation by mixed interpolation method

The operator splitting method is used to deal with the Navier-Stokes equation, in which the physical process described by the equation is decomposed into two processes： a diffusion process and a convection process; and the finite element equation is established. The velocity field in the element is described by the shape function of the isoparametric element with nine nodes and the pressure field is described by the interpolation function of the four nodes at the vertex of the isoparametric element with nine nodes. The subroutine of the element and the integrated finite element code are generated by the Finite Element Program Generator （FEPG） successfully. The numerical simulation about the incompressible viscous liquid flowing over a cylinder is carded out. The solution agrees with the experimental results very well.

一种矿用瓦斯管道设备防爆等级转换接口设计

针对煤矿瓦斯抽放监控系统中瓦斯管道设备及其相关联的电源和通信接口必须满足"ia"安全防爆等级要求,在现有"ib"防爆等级的煤矿瓦斯抽放监控系统基础上,通过增加一种安全等级转换接口对瓦斯管道设备进行了升级改造。详细介绍了具有梯形输出特性的阻性限流的电源转换原理和具有线性输出特性的阻性限流的信号转换原理,并对关键元件的相关参数进行了分析及计算。测试结果表明,该转换接口具有转换效率较高、频率失真小等特点,输出特性满足"ia"安全防爆等级要求。

Nonlinear Current-Voltage Characteristics and Electroluminescence of cBN Crystal

The current-voltage（I-V） characteristics of cBN crystal sandwiched between two metallic electrodes are measured and found to be nonlinear. Over 20 samples are measured at room temperature with various electrodes, and the resulting curves are all similar in shape. When a voltage of about 560V is applied to the cBN crystal, the emitted light is visible to the naked eye in a dark room. We explain these phenomena by the space charge limited current and the electronic transition between the X and Г valleys of the conduction band.

Intermittent blood flow restriction does not reduce atrophy following anterior cruciate ligament reconstruction

Background:A previous study has reported a 50% reduction in disuse atrophy of the quadriceps during the first 14 days after anterior cruciate ligament(ACL) reconstruction.A follow-up trial is needed to confirm these promising results.The present study aims to investigate the effect of an occlusion stimulus on quadriceps atrophy after ACL reconstruction.Methods:A total of 24 subjects participated in the study.They were randomized into two groups.Starting the 2nd day after surgery,the occlusion group received an occlusion stimulus for 5 min,followed by removal of the occlusive pressure for 3 min.This was repeated five times in one training session,twice daily.During the period of occlusive stimulus,the subjects performed 20 low load exercises for the quadriceps.The control group followed the same exercise protocol,but without the occlusion stimulus.Changes in quadriceps anatomical cross section area(ACSA) were measured using axial magnetic resonance(MR) images at 40% and 50% of the length of the femur.Results:Both groups had a significant reduction of quadriceps ACSA from 2 days before surgery to 16 days after surgery.During the intervention period,the occlusion group lost 13.8% ± 1.1%(mean ± SEM) and the control group lost 13.1% ± 1.0% of their quadriceps ACSA,respectively.There was no significant difference between the occlusion and control groups with regards to atrophy of the quadriceps muscles.Conclusion:In conflict with other studies using a similar protocol,application of blood flow restriction the first 14 days after ACL reconstruction did not reduce quadriceps ACSA muscle atrophy measured by MR in a population of athletes.

Current Limiting Characteristic Analysis of Magnetic-controlled Switcher Type Fault Current Limiter

A novel magnetic-controlled switcher type fault current limiter (FCL) based on the topology of the saturated iron core high temperature superconducting FCL is proposed. The magnetic field distribution of the FCL iron core is analyzed by FEA software ANSYS. The current limiting characteristic is investigated by both 3-D field-circuit coupled simulation and Matlab. The experiments on the 220 V/50 A test model show that the FCL can limit the fault current swiftly and effectively,and the FCL has the advantages of simple and reliable structure, flexible control strategy. The simulation and experimental results prove that the theoretical expectation and current limiting performance is satisfactory for practical use.

Numerical investigation of confined swirling gas-solid two phase jet

This paper presents a \%k\|ε\|k\-p\% multi\|fluid model for simulating confined swirling gas\|solid two phase jet comprised of particle\|laden flow from a center tube and a swirling air stream entering the test section from the coaxial annular. A series of numerical simulations of the two\|phase flow of 30 μm, 45 μm, 60 μm diameter particles respectively yielded results fitting well with published experimental data.

Network traffic flow evolution with battery electric vehicles and conventional gasoline vehicles

In order to investigate the effect of the use of battery electric vehicles on traffic dynamics,the valid paths of electric battery vehicles are defined and a check-based method is proposed to obtain them.Then,assuming that travelers only focus on their past travel experience,a day-to-day traffic assignment model is established based on reinforcement learning and bounded rationality.In the proposed model,the Bush-Mosteller model,a reinforcement learning model,is modified to calculate path choice probability according to bounded rationality.The modified model updates the path choice probability only if the gap between expected travel time and perceived travel time is beyond the cognitive threshold.Numerical experiments validate the effectiveness of the model and show that traffic flows can converge to the equilibrium in any case of cognitive thresholds and penetration rates of battery electric vehicles.The cognitive threshold has a positive influence on the variation of traffic flows while it has a negative influence on the differences between traffic flows.The adaptation of battery electric vehicles leads to the poor performance of the traffic system.

Development of control strategy of variable speed limits for improving traffic operations at freeway bottlenecks

A control strategy of variable speed limits(VSL)was developed to reduce the travel time at freeway recurrent bottleneck areas.The proposed control strategy particularly focused on preventing the capacity drop and increasing the discharge flow.A cell transmission model(CTM)was developed to evaluate the effects of the proposed VSL control strategy on the traffic operations.The results show that the total travel time is reduced by 25.5% and the delay is reduced by 56.1%.The average travel speed is increased by 34.3% and the queue length is reduced by 31.0%.The traffic operation is improved by the proposed VSL control strategy.The way to use the proposed VSL control strategy in different types of freeway bottlenecks was also discussed by considering different traffic flow characteristics.It is concluded that the VSL control strategy is effective for merge bottlenecks but is less effective for diverge bottlenecks.

Effect of polypropylene fiber and coarse aggregate on the ductility and fluidity of cemented tailings backfill

Adding polypropylene(PP)fibers and coarse aggregates has become a popular way to enhance the strength and stability of the cemented tailings backfilling(CTB)body.It is essential to explore the influence of tailings-aggregate ratio and fiber content on the mechanical properties of CTB samples.The comprehensive tests of the unconfined compressive strength(UCS),slump and microstructure were designed,and the regression models were established to characterize the effect of the strength,ductility and fluidity.The results indicate that the tailings-aggregate ratio of 5:5 and PP fiber content of 0.5 kg/m^(3) are the optimum point considering the UCS,cracking strain,peak strain and post-peak ductility.The tailings-aggregate ratio is consistent with the unary quadratic to the UCS and a linear model with a negative slope to the slump.Microstructural analysis indicates that PP fiber tends to bridge the cracks and rod-mill sand to serve as the skeleton of the paste matrix,which can enhance the compactness and improve the ductility of the CTB.The results presented here are of great significance to the understanding and application of coarse aggregates and fibers to improve the mechanical properties of CTB.

Strongly nonlinear long interfacial waves in uniform basic flows and their dispersion relationship

In this paper, long interfacial waves of finite amplitude in uniform basic flows are considered with the assumption that the aspect ratio between wavelength and water depth is small. A new model is derived using the velocities at arbitrary distances from the still water level as the velocity variables instead of the commonly used depth-averaged velocities. This significantly improves the dispersion properties and makes them applicable to a wider range of water depths. Since its derivation requires no assumption on wave amplitude, the model thus can be used to describe waves with arbitrary amplitude.

Analysis of one-dimensional consolidation of fractional viscoelastic saturated soils under continuous drainage boundary conditions

This paper presents the one-dimensional(1D)viscoelastic consolidation system of saturated clayey soil under continuous drainage boundaries.The fractional-derivative Merchant(FDM)model has been introduced into the consolidation system to simulate the viscoelasticity.Swartzendruber’s flow law is also introduced to describe the non-Darcian flow characteristics simultaneously.The generalized numerical solution of the 1D consolidation under continuous boundaries is given by the finite difference scheme.Furthermore,to illustrate the effectiveness of the numerical method,two simplified cases are compared against the current analytical and numerical results.Finally,the effects of boundary parameters and model parameters on the viscoelastic consolidation were illustrated and discussed.The results indicated that the boundary parameters have a significant influence on consolidation.The larger the values of boundary parameters,the faster the whole dissipation of the excess pore-water pressure and soils’settlement rate.Fractional-order and viscosity parameter have little effect on consolidation,which are primarily significant in the middle and late consolidation phases.With the increase of the modulus ratio,the whole consolidation process becomes faster.Moreover,considering Swartzendruber’s flow delays the consolidation rate of the soil layer.

Multigrid fictitious boundary method for incompressible viscous flows around moving airfoils

In this paper, an efficient multigrid fictitious boundary method （MFBM） coupled with the FEM solver package FEATFLOW was used for the detailed simulation of incompressible viscous flows around one or more moving NACA0012 airfoils. The calculations were carded on a fixed multigrid finite element mesh on which fluid equations were satisfied everywhere, and the airfoils were allowed to move freely through the mesh. The MFBM was employed to treat interactions between the fluid and the airfoils The motion of the airfoils was modeled by Newton-Euler equations. Numerical results of experiments verify that this method provides an efficient way to simulate incompressible viscous flows around moving airfoils.

Identifying Diffusion Limiting Current to Unravel the Intrinsic Kinetics of Electrode Reactions Affected by Mass Transfer at Rotating Disk Electrode

Rotating disk electrode systems are widely used to study the kinetics of electrocatalytic reactions that may suffer from insufficient mass transfer of the reactants.Kinetic current density at certain overpotential calculated by the Koutecky-Levich equation is commonly used as the metrics to evaluate the activity of electrocatalysts.However,it is frequently found that the diffusion limiting current density is not correctly identified in the literatures.Instead of kinetic current density,the measured current density normalized by diffusion limiting current density(j/jL)has also been frequently under circumstance where its validity is not justified.By taking oxygen reduction reaction/hydrogen oxidation reaction/hydrogen evolution reaction as examples,we demonstrate that identifying the actual diffusion limiting current density for the same reaction under otherwise identical conditions from the experimental data is essential to accurately deduce kinetic current density.Our analysis reveals that j/jLis a rough activity metric which can only be used to qualitatively compare the activity trend under conditions that the mass transfer conditions and the roughness factor of the electrode are exactly the same.In addition,if one wants to use j/jLto compare the intrinsic activity,the concentration overpotential should be eliminated.

Constitutive equations and finite element implementation of strain localization in sand deformation

A recently proposed model coupling with the solid-fluid of the saturated sand was utilized to study the deformation band. Based on the critical state plasticity model by Borja and Andrade, the hydraulic conductivity tensor was naturally treated as a function of the spatial discretization matrix about the displacement and the stress field, allowing a more realistic representation of the physical phenomenon. The fully Lagrangian form of the Darcy law was resolved by Piola algorithm, and then the flow law was gained, leading to the implementation of a modified model of the saturated sand. Then the criterion for the onset of localization was derived and utilized to detect instability. The constitutive model was implemented in a finite element program coded by FORTRAN, which was used to predict the formation and development of shear bands in plane strain compression of saturated sand. At last, the formation mechanism of the shear band was discussed. It is shown that the model works well, and the simulation sample bifurcates at 1.18% axial strain, which is in a good qualitative agreement with the experiment. The pore pressure greatly affects the onset and development of the deformation band, and it obviously increases around the localization-prone regions with the direction toward the outer side of the normal of the shear band, while the pore stress flows nearly horizontally and is distributed equally far away the shear band region.

Analysis of Linear Triangular Elements for Convection-diffusion Problems by Streamline Diffusion Finite Element Methods

This paper is devoted to studying the superconvergence of streamline diffusion finite element methods for convection-diffusion problems. In [8], under the condition that ε ≤ h^2 the optimal finite element error estimate was obtained in L^2-norm. In the present paper, however, the same error estimate result is gained under the weaker condition that ε≤h.

Numerical Heat Transfer Modelling for Rapid Impact Assessment of Limiting Thermostat Reliability on Fuel-Oil Burner Pre-Heaters： A Case Study

In this paper, the impact of limiting thermostat on the rupture event occuring in Fuel-Oil burner fuel pre-heaters＇ resistant （heat generating） wires is inspected numerically. Gaseous fuel content in the pipeline has also been issued as a possibility. Heater＇s inner temperature distributions have been simulated by an in-house MATrix LABoratory （MATLAB） script in order to understand the resistant wire exposure to high temperatures by numerous scenarios. It is concluded that the effect of fuel flowrate is not a major effect on the wires＇ fate because of the limiting thermostat co-working. The main difference between the calculations is the effect of thermostat cut off function. The numerical simulations enlightened the dominant effect of thermostat sensing delay, so the overheating event. Intolerable delay results with a quick drop in the thermal efficiency and an increased possibility on wire rupture due to overheating which means a burner malfunction. Referring to the first numerical simulation results, a distributed and reduced heat flux was implemented with the same fluid and thermodynamic properties on a revised pre-heater model with an increased heater plate. The increment, thus the reduction on the heat flux of the ribbon wires has been noted as the key for safe operation.

Hybrid Operation of Fault Current Limiter and Thyristor Controlled Braking Resistor

The effectiveness of a combination of fault current limiter and thyristor controlled braking resistor on power system stability enhancement and damping turbine shaft torsional oscillations has been studied. If both devices operate at the same bus, the stabilization control scheme can be carried out continuously and with flexibility. As a result, the fault currents are limited, and the generator disturbances and the turbine shaft torsional oscillations are converged quickly. In this paper, the effectiveness of the combination of both devices has been demonstrated by considering 3LG （three-lines-to-ground） fault in a two-machine infinite bus system. Also, temperature rise effect of both devices with various resistance values and weights has been demonstrated. Simulation results indicate a significant power system stability enhancement and damping turbine shaft torsional oscillations as well as with allowable temperature rise.