变压器直流电阻变化量特性统计分析

变压器直流电阻变化量是预防性试验中的一个关键指标,目前试验规程规定的阈值过于笼统,尚缺乏相关差异性的分析研究。针对此问题,利用数理统计方法分析了变压器直流电阻变化量的差异性。首先,统计了某地区127台变压器9年的直流电阻试验数据并计算其相邻年份变化量;其次,结合图示法与假设检验探索直流电阻变化量的分布规律;最后,利用置信区间分析不同维度直流电阻变化量的差异性。分析结果表明,按电压等级、容量大小、运行时间和运行环境湿度分类时,直流电阻变化量存在一定的差异,能够为该地区的变压器绕组状况评估提供借鉴。

(0~419.527)℃一等标准铂电阻温度计检定结果的不确定度评定

按照JJF1059.1-2012《测量不确定度评定与表示》的要求,对工作在(0~419.527)℃温区的一等标准铂电阻温度计检定结果的不确定度进行评定。包括电测设备引入的标准不确定度分量、标准铂电阻温度计在水三相点、锌凝固点、锡凝固点处阻值的标准不确定度分量,并最终计算电阻比的合成标准不确定度。

Skin temperature measurement method

To improve the accuracy of skin temperature measurements in thermal comfort research,a new measurement method based on a new thermometer is proposed.A platinum film resistance（Pt1000）sensor of the thermometer is welded on a printed circuit board to eliminate the heat loss from the leads and avoid the influence of the surrounding thermal environment.In order to determine the suitable thickness of the board,a steady heat conduction model is established.The simulation results reveal that when the thickness of the board is 0.2 mm,the influence of the surrounding air can be effectively prevented and the skin temperature does not obviously increase.The experimental results of verification show that the maximum measurement error of the skin temperature measured by the thermometer is 0.24 ℃,and the average measurement error of the skin temperature is 0.04 ℃.The proposed method provides an effective and reliable option for the skin temperature measurement in thermal comfort research.

Three-dimensional tensor controlled-source electromagnetic modeling based on the vector finite-element method

Scalar CSAMT is only suitable for measurements in one and two dimensions perpendicular to geological structures. For complex 3D geoelectric structure, tensor CSAMT is more suitable. In this paper, we discuss 3D tensor CSAMT forward modeling using the vector finite-element method. To verify the feasibility of the algorithm, we calculate the electric field, magnetic field, and tensor impedance of the 3D CSAMT far-zone field in layered media and compare them with theoretical solutions. In addition, a three-dimensional anomaly in half-space is also simulated, and the response characteristics of the impedance tensor and the apparent resistivity and impedance phase are analyzed. The results suggest that the vector finite-element method produces high-precision electromagnetic field and impedance tensor data, satisfies the electric field discontinuity, and does not require divergence correction using the vector finite-element method.

各向异性电子元件的欧姆定律

根据张量理论 ,计算了各向异性导电媒质在电流密度方向和电场强度方向的标量电阻率 .讨论了由各向异性导电媒质构成的电子元件的欧姆定律形式 ,分析发现其具有近似性 ,并不存在矩阵形式的欧姆定律 ,也不存在非线性电阻效应 .给出了基于欧姆定律的标量电阻特性普遍公式及其张量不变性记法 .

Fabrication and Characteristics of a Si-Based Single Electron Transistor

Si based single electron transistor (SET) is fabricated successfully on p type SIMOX substrate,based on electron beam (EB) lithography,reactive ion etching (RIE) and thermal oxidation.In particular,using thermal oxidation and etching off the oxide layer,a one dimensional Si quantum wire can be converted into several quantum dots inside quantum wire in connection with the source and drain regions.The differential conductance (d I ds /d V ds ) oscillations and the Coulomb staircases in the source drain current ( I ds ) are shown clearly dependent on the source drain voltage at 5 3K.The I ds V gs (gate voltage) oscillations are observed from the I ds V gs characteristics as a function of V gs at different temperatures and various values of V ds .For a SET whose total capacitance is about 9 16aF,the I ds V gs oscillations can be observed at 77K.

关于各向异性基本电子元件欧姆定律的两种形式

由于各向异性电阻元件的导电各向异性,使电流密度方向和电场强度方向不一致,从而欧姆定律表现为两种形式:电流密度方向的欧姆定律和电场强度方向的欧姆定律。相应地存在一个二阶电阻张量和一个二阶电导张量。并给出了它们的计算公式。分析表明各向异性电阻元件的欧姆定律具有近似性。

直流比较电桥装置与微计算机的连接方法

实现按元件检测直流电桥、直流电阻箱等类电阻量仪器的直流比较电桥装置,由于存在着数据处理繁杂、计算量大使检定效率不高的问题。从而使得用微计算机与电桥装置连接以实现电阻量仪器检定工作自动化这一内容成为电阻量测量领域的一项研究课题。本文将介绍有关使用通用系统机、单板机和单片机实现与比较电桥装置相连接的方法。一、连接方法微计算机与直流比较电桥装置连接的实质是利用装置中桥臂电阻换接开关状态编码器所产生的数字编码与计算机连接。 1.与z-80单板计算机连接连接电路如图1所示。

Study on mutual impedance characteristics between probes in a circular waveguide

The expression of mutual impedance between two probes in a circular waveguide is derived by means of a vector potential function, reaction concept and reciprocity theorem. The waveguide is semi-infinite, and one end of the waveguide is terminated to a load with a reflection coefficient. The contribution to the mutual resistance is found to come from the dominant mode, while the contribution to the mutual reactance comes from the dominant mode and the higher order modes. The major contribution to the mutual reactance is from the dominant mode, since the higher modes decay rapidly with the increasing the probes’ of separation distance. However, as the separation distance approaches zero, the higher modes become dominant, which results in a large value of the mutual reactance. The mutual impedance is dependent on the location and height of the probes, their separation distance and the location of the terminal plane.

Variable damping forces caused by electromagnetic energy harvesting with an adjustable load

A novel variable damper using an adjustable energy harvesting structure is proposed for semi-active vibration systems. The fluid flowing in a hydraulic cylinder is employed to drive an electromagnetic generator for harvesting vibration energy, which on the other hand, leads to a damping effect of the hydraulic damper. To make the damping force variable, an adjustable resistor is adopted to tune the capability of energy harvesting. The present approach is validated by both theoretical analysis and experimental evaluation. When connected with different resistance loads, the prototype damper has different equivalent damping coefficients ranging from 3. 987 × 104 to 2. 488 × 105 N· s/m. The results show that the damping force of the damper is variable in response to the adjustable load for the vibration energy harvesting.

金属铝管影响下磁共振耦合线圈特性参数变化

为了探究金属物体对磁共振耦合线圈自身特性参数的影响规律,针对现有理论模型不能完全描述金属铝管对线圈特性参数影响规律的问题,构建了金属铝管影响下的磁共振耦合单线圈修正模型,对应开展了仿真与实验研究,并给出了涡电流回路映射电阻R'E和电阻修正量RC具体表达式。研究规律表明:线圈电感参数变化量△L随间隙的增大而减小;线圈电阻参数变化量△R的变化趋势与间隙相关且存在变化趋势分界点,即当铝管与线圈间隙小于10 mm时,线圈电阻参数数值相对放置于空气中是增大的;当铝管与线圈间隙达到15 mm时,线圈电阻参数数值相对放置于空气中是减小的。

Resistivity measurement of conductive asphalt concrete based on two-electrode method

The objective of this work is to develop a novel methodology for determining real resistivity of conductive asphalt concrete based on two-electrode method.Due to an influence of contact resistance,the measured resistivity is always not equal to the real resistivity.To determine the real resistivity,a linear relationship of the measured resistivity,contact resistance and the real resistivity was established.Then experiments for six specimens with varying graphite contents were designed and performed to validate the formulation.Results of experiments demonstrate that the slope of the line represents contact resistance,and the intercept indicates the real resistivity.The effects of graphite content on contact resistance and real resistivity are also revealed.Finally,results show that the influence of contact resistance on accuracy of resisitvity measurement becomes more serious if graphite content is beyond 3%.Hence,it is the time to choose this novel methodology to determine the real resistivity of asphalt concrete by taking account of contact resistance.

Application of Wenner Configuration to Estimate Soil Water Content in Pine Plantations on Sandy Land

To estimate the mean value of surface soil water content rapidly,accurately,and nonintrusively,field investigations on soil electrical resistivity(SER)with the Yokogawa 324400 earth resistivity meter and the surface(0-150 cm)soil water content(SWC)with time domain reflectometry(TDR),together with the abiotic factors including soil texture,structure. and salinity concentrations were conducted in the Mongolian pine(Pinus sylvestris var.mongolica)plantations on a sandy land.The measurement of SER was based on the 4-probe Wenner configuration method.Relationships between the values of SWC and SER were obtained based on analysis of the abiotic factors of the research site,which play a key role in affecting the soil electrical resistivity.Results indicate that the SER meter could be used to estimate the mean value of SWC in the Mongolian pine plantations on the sandy land during the growing seasons.The bulky nature of the equipment simplified the cumbersome measurements of soil water content with the general methods.It must be noted that the Wenner configuration method could only provide the mean values of the SWC,and the soil texture,structure, temperature,and solute concentrations influenced the SER and further affected the estimation of the SWC by the SER meter.Therefore,the results of this study could be applied on a sandy land during the growing seasons only.However, the SWC of other soil types also may be obtained according to the individual soil types using the procedures of this study.

Key parameters controlling electrical resistivity and strength of cement treated soils

The improvement of question soils with cement shows great technical, economic and environmental advantages. And interest in introducing electrical resistivity measurement to assess the quality of cement treated soils has increased markedly recently due to its economical, non-destructive, and relatively non-invasive advantages. This work aims to quantify the effect of cement content （aw）, porosity （nt）, and curing time（T） on the electrical resistivity （p） and unconfined compression strength （UCS） of cement treated soil. A series of electrical resistivity tests and UCS tests of cement treated soil specimen after various curing periods were carried out. A modified Archie empirical law was proposed taking into account the effect of cement content and curing period on the electrical resistivity of cement treated soil. The results show that nt/（aw·T） and nt/（aw·T^1/2） ratio are appropriate parameters to assess electrical resistivity and UCS of cement treated soil, respectively. Finally, the relationship between UCS and electrical resistivity was also established.

Quantum current and Coulomb blockade effect in the mutual inductance coupled mesoscopic system with active source

Based on the charge discreteness,the property of quantum current and the effects of Coulomb blockade have been investigated for the mutual inductance coupled mesoscopic system with active source in external magnetic field.The relationships between quantum current and the conditions of Coulomb blockade in the coupled dual-ring system are given here.

Resistivity in Formation and Decomposition of Natural Gas Hydrate in Porous Medium

A new one-dimensional system for resistivity measurement for natural gas hydrate(NGH)exploitation is designed,which is used to study the formation and decomposition processes of NGH.The experimental results verify the feasibility of the measurement method,especially in monitoring the nucleation and growth of the NGH. Isovolumetric formation experiment of NGH is performed at 2°C and 7.8 MPa.Before the NGH formation,the initial resistivity is measured to be 4-7Ω·m,which declines to the minimum value of 2-3Ω·m when NGH begins to nucleate after the pressure is reduced to 3.3 MPa.As the NGH grows,the resistivity increases to a great extent,and finally it keeps at 11-13Ω·m,indicating the completion of the formation process.The NGH decomposition experiment is then performed.When the outlet pressure decreases,NGH begins to decompose,accordingly,the resistivity declines gradually,and is at 5-9Ω·m when the decomposition process ends,which is slightly higher than the resistivity value before the formation of NGH.The occurrence and distribution uniformity of NGH are determined by the distribution and magnitude of the resistivity measured on an one-dimensional sand-packed model.This study tackles the accurate estimation for the distribution of NGH in porous medium,and provides an experimental basis for further study on NGH exploitation in the future.

Preparation and properties of pitch carbon based supercapacitor

Using the mesophase pitch as precursor, KOH and CO2 as activated agents, the activated carbon electrode material was fabricated by physical-chemical combined activated technique for supercapacitor. The influence of activated process on the pore structure of activated carbon was analyzed and 14 F supercapacitor with working voltage of 2.5 V was prepared. The charge and discharge behaviors, the properties of cyclic voltammetry, specific capacitance, equivalent serials resistance （ESR）, cycle properties, and temperature properties of prepared supercapacitor were examined. The cyclic voltammetry curve results indicate that the carbon based supercapacitor using the self-made activated carbon as electrode materials shows the desired capacitance properties. In 1 mol/L Et4NBF4/AN electrolyte, the capacitance and ESR of the supercapacitor are 14.7 F and 60 mΩ respectively, The specific capacitance of activated carbon electrode materials is 99.6 F/g; its energy density can reach 2,96 W.h/kg under the large current discharge condition, There is no obvious capacitance decay that can be observed after 5000 cycles, The leakage current is below 0,2 mA after keeping the voltage at 2.5 V for l h, Meanwhile, the supercapacitor shows desired temperature property; it can be operated normally in the temperature ranging from -40 ℃to 70 ℃,

Resistivity and thermal infrared precursors associated with cemented backfill mass

The stability of cemented backfill mass is important to keep miners and equipment safe in underground backfill miming.The stress-strain behavior, resistivity and thermal infrared(TIR) characteristics of backfill mass under uniaxial compression were investigated. The monitoring system consisted of a TIR observation system, a stress-strain monitoring system and a resistivity measurement system. Precursory information for impending failure of cemented backfill mass was collected, including TIR, strain and resistivity precursors. The sensitivity and difference of different monitoring information to the same failure event were compared.The results show that the time-space evolution process of the resistivity and TIR is basically the same as the whole process from compression deformation to failure of backfill mass, and the time variation of resistivity and TIR is obviously characterized by stage.The resistivity precursor turns out earlier than the TIR and the strain. The resistivity relation with loading compression is anti-symmetry, decreasing as the compression stress increases before the peak strength of backfill mass. However, when the backfill mass enters into the phase of failure, the resistivity starts to increase as the stress increases. The change of the resistivity growth direction can be regarded as the resistivity-caution-point for the failure of backfill mass under uniaxial compression. It is also indicated that the TIR information mainly represents the surface temperature evolution in the process of compression before the backfill enters into the plastic-yield state. It can be a valuable tool to obtain the precursors for failure of cemented backfill mass for backfill mines.

Inversion of thicknesses of multi-layered structures from eddy current testing measurements

Luquire et al. ' s impedance change model of a rectangular cross section probe coil above a structure with an arbitrary number of parallel layers was used to study the principle of measuring thicknesses of multi-layered structures in terms of eddy current testing voltage measurements. An experimental system for multi-layered thickness measurement was developed and several fitting models to formulate the relationships between detected impedance/voltage measurements and thickness are put forward using least square method. The determination of multi-layered thicknesses was investigated after inversing the voltage outputs of the detecting system. The best fitting and inversion models are presented.

On-line Measurement for Ohmic Resistance in Direct Methanol Fuel Cell by Current Interruption Method

Electrochemical impedance spectroscopy (EIS) is widely used in fuel cell impedance analysis. However, for ohmic resistance (R Ω), EIS has some disadvantages such as long test period and complex data analysis with equivalent circuits. Therefore, the current interruption method is explored to measure the value of RΩ in direct methanol fuel cells (DMFC) at different temperatures and current densities. It is found that RΩ decreases as temperature increase, and decreases initially and then increases as current density increases. These results are consistent with those measured by the EIS technique. In most cases, the ohmic resistances with current interruption (R iR ) are larger than those with EIS (R EIS ), but the difference is small, in the range from –0.848% to 5.337%. The errors of R iR at high current densities are less than those of R EIS . Our results show that the R iR data are reliable and easy to obtain in the measurement of ohmic resistance in DMFC.