Analysis of the transient Joule heating effect in a conductive-bridge random-access memory (CBRAM) using a single-phase-lag (SPL) model

The main objective of this work is to study the transient Joule heating effect in a conductive-bridge random-access memory (CBRAM) using the single-phase-lag heat conduction model to describe the effects of the metallic conductive filament (CF) radius and the reset voltage on the thermal and electric field. The results reveal that the CF geometry plays an important role in the transient Joule heating. The heat wave of fast transient conduction is stronger in the narrow region of the CF during the reset process for a high applied voltage and a small top radius of the CF. It is demonstrated that the presented model can predict the nanoscale heat transfer in the transient state and during the reset process in the CBRAM. Finally, numerical computations are carried out using the finite-element method to solve the nonlinear heat conduction equations.

     

导线临界防冰电流及其影响因素分析

导线覆冰是影响输电线路安全运行的主要问题之一,基于焦耳热效应的临界电流防冰方法可行且有效。为此,基于焦耳热效应和导线在临界覆冰状态下的传热过程,并考虑了集肤效应、导线几何外形及其表面水膜对传热过程的影响,建立了临界防冰电流模型,其计算结果与人工气候室试验结果符合。另外,还研究了在覆冰环境下,导线直径及几何外形、环境温度、风速、液态水含量(LWC)、中值体积直径(MVD)对输电线路临界防冰电流的影响。仿真结果表明,临界防冰电流随温度的降低或风速的增加而迅速增大,随LWC的增大或MVD在0～100μm区间增大而缓慢增大,而当MVD>100μm时,临界防冰电流无明显变化。     

Reset switching statistics of TaO<Subscript>x</Subscript>-based Memristor

In this work, the resistance switching mechanism of Reset process has been suggested through the statistics of the reset voltage and the reset current, which is consistent with the thermal-activated dissolution model. Furthermore, the variability nature of the switching parameters has been analyzed by screening the statistical data into different resistance ranges and the distributions are shown to be compatible with a Weibull distribution. Finally, we propose criteria for selecting high-performance memristor materials based on the statistical results and the temperature evolution of the conductive filament (CF) in three different memristor materials (TaO_x, HfO₂ and NiO). The high-performance materials tend to exhibit a higher Weibull slope and there are no variation and extra heat generated in the CF before the reset event.     

Closed solution of the transient skin effect in induction machines

The transient skin effect is solved for the rectangular open and semi closed slots containing a massive conductor. The solution is applied to the Joule losses and to the analytical calculation of the air gap torque and the stator currents of the induction machine exposed to the three-phase short circuit. The calculation of the Joule power losses under transient conditions has been accomplished, especially, for induction machines of the middle- and high-power range. This becomes important in dynamically controlled induction machines, especially when torque cycles of approximately 100 ms or less occur. Never before have the copper losses been evaluated completely under these transient conditions. For the calculation of the losses, the direct proportionality of the losses between torque and rotor bar current can be used. Furthermore, the results of the transient skin effect can find application in the operational behavior of the induction machine. The consideration of the transient skin effect of the rotor is necessary for calculating currents and torques. Until now, state of the art has only provided an analytical solving of the skin effect free model. Aiming to apply the given rotor geometry, this paper derives an approach which includes the transient skin effect, applying it on the three-phase short circuit of the idle running induction machine.     

Entropy production and the temperature equation in electrohydrodynamics

The equation for the temperature in moving dielectric fluids is obtained in most texts and papers dealing with electrothermohydrodynamics by simply adding the Joule heating, and more exceptionally by adding also the dielectric heating. Here we derive this equation rigorously from first principles. First, we derive the entropy production, and then we show that additional terms depending on the electric field are present in the equation for the temperature. Among them we have terms of thermoelectric origin, and terms depending on the variation of permittivity with temperature, in addition to Joule and dielectric heating. The different terms in this equation are discussed in detail, and are given a clear physical interpretation.     

Proximity effect and eddy current losses in insulated cables

Insulated cables are generally designed according to thermal criteria: the current rating depends on the permissible temperature inside the insulation. As the heating of a cable mainly results from Joule losses, it is worthy to determine the current distribution in its metallic components (the core and the metallic screen for single core cables). The current distribution in tables is affected by the skin effect and the proximity effect due to neighbouring cables of the circuit itself or from parallel links. A general method is developed to calculate the current distribution in the core and the screen of a single-core cable, starting from Maxwell equations. The stress is set upon skin and proximity effects, taking into account the influence of the frequency. Joule losses are calculated in some practical cases of three-phase links     

不同载流条件下滑动电接触特性

不同载流情况下,引起滑动接触面温升的主要因素有摩擦热、焦耳热、电弧热.接触面的温升使接触材料表面发生物理化学变化,从而改变了接触面成分,同时反过来影响接触面的滑动电接触性能.论文通过对铜基粉末冶金滑板、浸铜碳滑板两种滑板材料与铜锡导线的对磨实验,分析了两种滑板材料在受流摩擦时的磨损行为.研究表明:随着电流的增大,两种滑板材料的接触电阻、温度以及磨耗率都在增大,浸铜碳滑板材料的接触电阻变化率较小,但接触表面的温度偏高,该滑板磨耗率变化较小,受流磨损性能较好.     

覆冰交流输电线路保线电流及其影响因素分析

建立了导线覆冰过程的热平衡方程,同时考虑绞线几何外形及集肤效应对传热过程的影响,提出了基于焦耳热效应的输电线路导线保线电流计算公式,并采用Runge-Kutta算法对水滴运动轨迹进行模拟,得到碰撞系数这一关键参量值。仿真结果表明,保线电流是导线外径、导线电阻、表面几何外形等导线自身参数以及环境温度、风速、水滴中值体积直径、空气中液态水含量等大气参数的函数;得到了不同绞线在典型覆冰类型下的保线电流,与人工气候室的试验结果相吻合。将该模型的预测结果与其他模型进行了比较,进一步证明该模型的准确性。     

Physical mechanisms of tissue injury in electrical trauma

The author reviews data indicating that skeletal muscle cell rupture may result from either heating or electroporation due to electric shock and discusses their relative contributions to tissue injury in electrical trauma victims. It is concluded that the relative contributions of these mechanisms are probably dependent on the duration of electric current passage, the geometry of the cells, their location, and other factors. If the contact is brief, nonthermal mechanisms of cell damage may be most important. If the contact is much longer, heat damage will be most destructive. The characteristic time before heat damage predominates is probably a function of the electric field strength in the tissue. The various factors involved should also influence the pattern of injury because damage by Joule heating is not known to be dependent on cell size     

计及故障持续时间的换流变压器阀侧单相接地故障分析

换流变压器阀侧单相接地故障发生时刻具有随机性,其相对于换流阀通断时刻的位置不同,会导致不同的暂态过程。首先提出了类换相失败的概念,以换相失败和类换相失败为切入点,在将故障发生时刻分段的基础上,考虑了瞬时性故障时,故障持续时间对于换流器暂态过程的影响。理论分析和仿真验证表明,换流变压器阀侧高压桥发生故障时,会立即造成类换相失败的发生,而低压桥瞬时性故障时,可能不对外体现故障特征。     

考虑温度再设的暖通空调电力需求响应策略研究

近年来,空调负荷的急剧增长已经成为季节性电力紧张的最主要原因,利用空调需求响应策略,调整空调负荷对于实现电网削峰填谷有重要意义。以风机盘管加新风形式的空调系统为对象,建立其TRNSYS仿真模型,基于分时电价政策,针对温度再设需求响应策略进行研究,采用再次设定制冷区域温度和热舒适指标两种策略,对比其在需求响应期间的峰值负荷削减量和整体系统运行的费用。结果表明基于温度再设的需求响应策略峰期负荷转移率约为30.3％,基于热舒适指标控制的需求响应策略的峰期负荷转移率约为22.7％,然而,这两种策略并不能节省电费,因此,除了分时电价的优惠政策外还需要给予相应的激励措施。     

煤颗粒在快速升温过程中非傅立叶导热效应的计算研究

电站锅炉煤粉燃烧过程中，煤粉着火前期的升温速率可达10^4K/s。而且煤粉在着火前期的升温状态直接影响到煤粉挥发份的释放速度和挥发份成分，进而影响到煤粉颗粒的着火和燃烧。该文针对煤颗粒快速升温过程中非傅立叶导热效应，利用热波模型和D－P－L模型对快速升温过程中煤颗粒的温度场进行的数值模拟，与实测结果进行了比较。并发现对于电站锅炉所燃用煤粉的粒径范围，在煤粉着火前的升温过程中考虑非傅立叶导热效应是十分必要的。     

Electrical and optical properties of metal-insulator-transition VO2 thin films

Vanadium dioxide thin films were deposited using in situ pulsed laser deposition technique on a-, c-, and r-plane Al₂O_3, and MgO(100) substrates. Microstructure of the films was varied between epitaxial VO₂, polycrystalline VO₂, mixtures of VO₂ and V₆O₁₃ with VO₂ as the main phase, and mixtures of VO₂ and V₆O₁₃ with V₆O₁₃ as the main phase by controlling the deposition oxygen partial pressure. Detailed XRD, SPM, and FESEM measurements were performed in order to analyze the structure of the films. Resistivity as a function of temperature, current–voltage characteristics in electric current induced Joule heating transition process, and the optical transmittance both in insulator and metal states were measured. MIT effect led to 10³–10⁵ change in resistivity with varying transition temperature and hysteresis loop widths. The largest and the steepest transitions were found in the films with polycrystalline microstructure deposited at higher oxygen pressures. Epitaxial films had 2.5 times higher insulator state conductivity than polycrystalline films, which lead to a clearly smaller switching powers in MIT effect generated by Joule heating. However, the optical properties in both states were not considerable affected by conductivity or microstructure properties. The relationships between the microstructure, electrical and optical properties, as well as MIT switching effect together its dynamics in the films are discussed.     

小功率连接器温度采集系统的设计与实现

一种应用于家用电器中的小功率连接器在整机例行实验过程中烧坏失效。分析发现其运行过程中触点界面发生微动腐蚀,导致接触电阻升高,产生过多焦耳热是造成其失效的重要原因。为了监测微动过程中的温度变化,本论文设计了一套简单实用的连接器温度采集系统。采用凌阳SPCE061A作为主控板,Pt100温度传感器作为前端采集装置,所采集的温度信号通过UART模组传送至上位机进行温度显示。通过实时监控连接器微动过程温度值的变化,验证了微动腐蚀导致的接触电阻升高是造成连接器失效的直接原因。     

油纸绝缘微水二次扩散过渡过程的分析

以菲克第二定律为基础建立数学模型,分析了变压器油纸绝缘纸中水分一次扩散未达到稳态时,外部条件改变导致绝缘纸中稳态水分含量改变,进而引发的绝缘纸中水分发生二次扩散过程。重点分析了由于一次扩散不充分引起的二次扩散过程中的过渡过程,并进行了实验验证。提出表征二次扩散过渡过程的特征量,即过渡时间和相对误差。过渡时间是从二次扩散开始到绝缘纸中水分扩散方向处处一致的时间,受温度、纸厚和一次扩散平衡率的独立作用;相对误差是以一次扩散水分均值作为二次扩散水分起始分布造成的误差,相对误差峰值表征二次扩散过渡过程的强度,受一次扩散平衡率、二次扩散稳态水分含量影响,相对误差峰值时间表征二次扩散过渡过程的速度,受温度和纸厚的影响。     

Charge buildup in lossy dielectrics with induced inhomogeneities

In addition to their normal inhomogeneities, insulation may also become inhomogeneous under stress, for instance if their temperature is not uniform. Then, a charge density builds up wherever material properties such as conductivity and permittivity are not uniform. This is the case of HVDC cables, in which the core is heated by the Joule effect, while the sheath remains at near ambient temperature, so that an average temperature gradient of ⩽50 K/cm may occur in the insulation, under a field which can reach 100 kV/cm. If the conductivity of the insulation is assumed to depend only on temperature, with an activation energy of 1 eV, the steady charge density predicted by electrostatics may reach levels easily measurable by the techniques now available. This charge density is somehow lowered in non-ohmic insulation. An early analysis of the transient charge build-up is discussed here, and extended to the case of a non-ohmic insulation. This allows calculation of the transient current generated in the external circuit by the accumulating charge, in the cases of ohmic and non-ohmic insulation. Finally, other manifestations of the space charges in question are mentioned. Among these, unexpected results on electroconvection in slightly ionic liquids in the presence of a temperature gradient are analyzed in terms of these charges, and suggest practical applications     

Hydrodynamic model for electrical arc modelling [in circuitbreakers]

A hydrodynamic model for electrical arc modelling is presented. The model, which takes into account Joule heating, radiation, Laplace forces, arc-wall interactions and real gas effect, has been validated through comparisons with measurements. Industrial applications have already been computed and concern high, medium and low voltage circuit breakers     

热网特性对于综合能源系统超短期调度的影响

综合能源系统中的热网和电网在传输时延和传输损耗等方面存在显著差异。文中着重研究热网特性对于系统超短期调度的影响,首先基于图论建立适用于系统优化调度的热网模型,重点研究热媒温度的暂态变化特性,推导出依据调度周期和管段长度判断管段暂/稳传热特性的公式。随后分别对比三种情景下(考虑热网暂态传热特性、仅考虑热网稳态传热特性和不考虑热网传热特性)设备的最优运行状态、日运行成本和模型求解时间。研究结果表明,热网复杂的拓扑结构和传输时延造成的蓄热特性改变了系统热功率的供求匹配机理,使得热源端和负荷端的供、求热功率不再实时匹配。考虑热网暂态传热特性前后,燃气锅炉的最优出力和热网的供水温度变化显著,可见在系统超短期调度环节应考虑热网暂态传热特性。     

交流电场对绝缘子覆冰形成的影响机理

在人工气候室内试验研究了不同类型覆冰条件下XP-160绝缘子的覆冰情况及电气特性,并根据试验结果分析了电场对绝缘子表面干、湿增长覆冰影响的机理。结果表明：电场对绝缘子覆冰的影响与环境温度、空气中过冷却水滴直径和电场强度有关。电场对覆冰影响的主要表现是焦耳热效应和几种与电晕放电相关的机理;电场对干增长覆冰影响的主要表现是电场力的吸附作用、极化作用及冰枝的电晕放电和沉积放电。     

对流与辐射对电磁继电器内部温度场影响的仿真研究

随着继电器等电器装置小型化、大容量的快速发展,继电器等电器内部温度场的分析与优化变得越来越重要。本文利用ANSYS软件分析仿真了继电器工作周期为6s（3s通3s断）时内部暂态温度场的分布,计算了内部元件辐射与对流系数,仿真了继电器工作100个周期时的内部温升变化规律及对流与辐射对内部温升的影响强度。结果表明,对流与辐射在短时间内（操作次数少）对内部温升影响很小,当操作次数增加较多（工作时间长）时则其影响较大,但二者共同作用的总效应对内部温升变化的影响一般小于30％,即金属导体及其热回路是继电器内部温升高低的决定性因素。