Control of Electrical Energy Distribution in a Cable Channel

The load distribution between 18 cable lines located in an underground cable channel is considered. It is found that a current distribution control system in the cable channel needs to be developed to optimize the load conditions, as well as prevent possible overheating. The possibility of using a mathematical model of heat and mass transfer processes in the channel to determining the optimal current loads of cable lines is considered. A mathematical model of heat and mass transfer processes in the cable channel is constructed that makes it possible to study the temperature conditions of the channel under different configurations and line loads. Search algorithms of optimal operating currents under varying loads are developed that take into account the requirements for permissible temperatures and categories of consumers. The unsteady condition of overload of one of the lines due to an emergency is investigated. The heating curves of current-carrying conductors of the emergency cable line and those adjacent to it are plotted. The value of the current is determined to which it is necessary to reduce the load in one of the lines to maintain the system operability.     

Mathematical modeling of nonstationary processes of heat and mass transfer in a rectangular cable channel

This work is devoted to solving the problem of heat and mass transfer in a rectangular cable channel laid in the earth mass, taking into account the electric and magnetic dynamics processes in the metal elements of the power cable. The current load of power cables depends on the temperature field in the cable construction, which in turn the following factors influence: the conditions of heat transfer, thermal characteristics of the materials used, the induced currents in a metal screen of power cables, etc. The proposed mathematical model of the processes of complex heat and mass transfer is based on the laws of conservation of mass, momentum, and energy. For the electrodynamics problem, equations of current density and a magnetic potential vector based on Maxwell equations are used. The problem was solved numerically under conditions of natural convection with taking into account the radiant energy by the finite element method in the Ansys Fluent software package. As a result, the power of heat losses in the metal structural elements of the power cable and the velocity and temperature fields in the cable channel were calculated. The temperature fields in the cable channel are presented and analyzed depending on the location of power cables. The different operating modes of the cable line are discussed. To analyze the heat processes in the cable channel, the nonstationary problem defining the heating time of cable lines to the limit values is solved. The heating curves of the cable lines operating in unsteady mode are obtained. The maximum operating time of the cable line in an overload and short circuit is determined.     

Selection of permissible current loads of power cables located in cable channels taking into account losses in the protective metal screens

A mathematical model of a complex process of heat transfer in a cable channel under conditions of natural convection is proposed. The influence of the metal protective screens on the operating temperature of cable lines is estimated, and the carrying capacities at the different section of the screens are calculated.     

Determination of the optimal working conditions of cable lines in an underground cable channel

Mathematical modeling of heat transfer processes inside a cable channel taking into account natural convection and radiation between the cable surface and tube and the loss in shields was carried out. An underground cable channel consisting of eight lines with a voltage of 6 kV and six lines with a voltage of 35 kV was investigated. The conductor section is 150 mm². Cables of APvVng-LS brand were placed in a triangle inside polyethylene tubes. The patterns of temperature fields obtained under variance of different various factors were determined, the permissible currents were calculated, and the optimal circuits of connection of cable lines depending on the selected criterion were proposed. The two-dimensional nonstationary problem of complicated heat and mass transfer and heat conductivity inside the underground cable channel was solved by the finite elements method using the ANSYS software package. The range of permissible operating currents depending on the location of cable lines and priority of their connection was determined. The effect of the temperature of the environment on the permissible current was considered. The optimal ranges of thermal permissible currents taking into account the shield loss were calculated. The optimal connection circuits of the cable lines depending on the problem being solved were obtained. An estimation of transferred power for every considered connection method is presented. Conclusions for practical application of the method of connection of the cable line were drawn. The fields of application of this mathematical model were proposed.     

Short-Term Transient Temperature Calculations and Measurements for Underground Power Cables

A time-dependent heat transfer model based on the complete Fourier integral was developed for calculating cable temperatures during short-term transient conditions. A cyclic heat transfer calculation is used to obtain the initial temperature-time profile of the cable before the transient loading begins. The short-term transient model uses a lumped parameter formulation for the different cable regions and the Fourier integral to approximate the transient heat loss profile. Calculated conductor, jacket, and conduit temperatures show reasonable agreement with experimental results for a number of short-term transient tests with cables in a typical duct bank arrangement.     

暂态负荷下高压直流海底电缆热传递过程

高压直流（HVDC）交联聚乙烯（XLPE）绝缘海底电缆是实现长距离和大容量电能输送的重要设备。HVDC海底电缆负荷影响温度分布,而温度对HVDC XLPE绝缘电导率和电场强度分布特性有重要影响。相对于稳态负荷条件,暂态负荷条件下HVDC海底电缆热传递过程更加复杂。为研究暂态负荷下HVDC海底电缆热传递过程,建立热学有限元模型,仿真分析HVDC海底电缆由零负荷向满负荷再向零负荷转变过程的热传递过程,并组建试验平台开展对比研究。研究结果表明：仿真计算结果和试验测试结果吻合度高,仿真模型适用于描述暂态负荷下HVDC海底电缆热传递过程;通过构建导体温度暂态分量和稳态分量,可以实现良好的导体温度热传递过程趋势拟合,拟合方法有利于指导HVDC海底电缆温度趋势预测和现场运行维护工作。     

暂态负荷下高压直流海底电缆热传递过程

高压直流（HVDC）交联聚乙烯（XLPE）绝缘海底电缆是实现长距离和大容量电能输送的重要设备。HVDC海底电缆负荷影响温度分布,而温度对HVDC XLPE绝缘电导率和电场强度分布特性有重要影响。相对于稳态负荷条件,暂态负荷条件下HVDC海底电缆热传递过程更加复杂。为研究暂态负荷下HVDC海底电缆热传递过程,建立热学有限元模型,仿真分析HVDC海底电缆由零负荷向满负荷再向零负荷转变过程的热传递过程,并组建试验平台开展对比研究。研究结果表明：仿真计算结果和试验测试结果吻合度高,仿真模型适用于描述暂态负荷下HVDC海底电缆热传递过程;通过构建导体温度暂态分量和稳态分量,可以实现良好的导体温度热传递过程趋势拟合,拟合方法有利于指导HVDC海底电缆温度趋势预测和现场运行维护工作。     

考虑轴向传热的单芯电缆线芯温度实时计算模型研究

为了研究轴向传热对电缆线芯温度的影响,首先以单芯电缆的三维微元热路模型为基础,建立了考虑单芯电缆轴向与径向传热的三维热路模型,且根据该三维热路模型实现了单芯电缆线芯温度实时计算的理论推导。其次,通过不同敷设环境下分别加载恒定与阶跃电流的实验,讨论了电流、电缆敷设环境与外界环境温度等因素对轴向、径向温度分布的影响。实验结果表明,电流是决定轴向温度梯度变化趋势的主要因素,空气中电缆的线芯温度上升速度最快,土壤中电缆次之,水中电缆最慢。最后通过有限元仿真工具,对比了空气中电缆中间接头三维有限元模型与二维有限元模型计算的线芯温度。研究结果表明,只考虑电缆径向传热的二维热路模型会造成线芯温度计算的误差,而考虑电缆轴向与径向传热的三维热路模型能够提高计算的精度。     

电力电缆接头温度场分布的理论研究

电力电缆接头事故在电力电缆故障中占很大的比例,电力电缆接头的温度是反应其运行状态的重要参数。文中构建了电力电缆接头的简化结构模型,运用传热学的原理建立了电力电缆接头的温度场数学模型,应用有限元法分析了电力电缆接头的温度场分布。根据温度场的分布,把温度传感器合理地安装在接头的表面,可以通过电力电缆接头的结构特性、表面温度和环境温度,得到更加接近实际温度的接头线芯温度,能够及时准确地了解电力电缆接头的运行状况。     

单芯电缆线芯温度的非线性有限元法实时计算

考虑电缆材料热性参数是温度的函数及忽略热量沿着线芯轴向传输所造成的线芯温度计算误差,为提高电缆线芯温度计算的精度,提出基于非线性有限单元法计算电缆导体的温度。研究电缆导体径向、轴向温度梯度以及热量扩散规律,分析运行电流、外界环境温度等因素对电缆线芯轴向、径向温度分布的影响。根据传热学原理,研究电缆热性参数随温度变化对电缆导体温度的影响,建立电缆导体温度计算三维非线性有限元模型,并通过实验数据对非线性有限元模型进行验证和修正。实验和有限元仿真的对比表明：忽略电缆热量沿着轴向传输以及热性参数的改变会造成线芯温度计算误差;所提出的电缆导体温度实时计算非线性有限元模型的有效性,为高温下运行电缆导体温度监测与负荷预测奠定了基础。     

基于温度场的单芯电缆载流量研究

导体温度是电力电缆载流量幅值变化的最直接特征量,电缆表面温度和线芯温度是反应电缆运行情况的重要参量。在简化内热源的基础上,建立单芯交联聚乙烯电力电缆的传热模型;通过研究稳态时电缆温度场分布,分析温度参量之间的关系和影响载流量的因素;基于这个传热模型,优化影响因素,对提高电缆安全运行的可靠性和载流量最优化配置有重要的指导意义。     

航天器热试验加热电缆绝缘自动测试系统的设计

为实现航天器热试验外热流模拟装置与航天器之间绝缘性能的检测,对加热电缆绝缘自动测试技术进行研究,设计了一套基于PXI的航天器热试验加热电缆绝缘自动测试系统.该系统采用继电器矩阵技术设计了加热电缆输入通道切换装置,基于PXI总线仪器实现了多芯电缆自动扫描以及对地绝缘电阻的测量,并采用VC++ 6.0开发了系统上位软件.测试结果表明,该系统能够在短时间内完成最多8根加热电缆的对地绝缘检测,结果准确、运行可靠,大大提高了加热电缆绝缘电阻测试的自动化水平.     

地下电力电缆隧道通风系统的模拟计算

应用CFD软件对地下电力电缆隧道的通风散热系统进行模拟计算,分析其不同换气次数工况下的散热效果以及温度、速度分布。结果表明,电力电缆隧道的通风系统能有效带走电缆产生的热量。随着风量的增加,散热量得到了小幅提升,大量空气未经完全换热就从中间低阻通道流走。建议优化电缆布置,避免电缆紧贴舱室壁面。     

电缆沟敷设方式下电缆温度场计算模型

针对电缆沟敷设方式下电力电缆的广泛应用以及传统方法载流量计算参数较难确定的不足,根据传热学的基本原理,利用有限单元自动划分法,建立了一种基于有限元法的电缆载流量计算模型,能够按照实际敷设情况的变化对模型参数进行修改。根据电缆的结构参数和周围敷设区域的物性参数分析了电缆沟中电缆区域温度场分布情况,并提出了一种基于二分法来计算电缆载流量的方法。可为优化电缆敷设方案提供理论依据。     

电线电缆破损的定量热像检测与诊断方法研究

通过控制容积法对带有破损的高压输电线及电缆建立了物理和数学模型.模型考虑了电线和电缆芯的轴向导热,更精确地描述了破损程度和温度响应的关系;得到了无破损以及不同程度破损时电线以及电缆的表面温度分布规律;提出了通过红外热像仪测量表面温度分布在线检测与诊断输电线和电缆破损程度的方法,并针对常用电线电缆进行了具体分析和诊断.理论和实验研究均证明了红外在线检测电线电缆破损的可行性及定量诊断方法的有效性.     

电缆沟敷设方式下电缆载流量计算及其影响因素分析

根据传热学的基本原理,利用有限单元自动划分法,建立了一种基于有限元法的电缆载流量计算模型,能按照实际敷设情况的变化对模型参数进行修改。根据电缆的结构参数和周围敷设区域的物性参数分析了电缆沟中电缆区域温度场分布情况,并提出基于二分法计算电缆载流量的方法。对比分析结果表明,相对于IEC60287中的热路法,该模型不仅计算结果准确,而且能更方便地考虑外界环境因素对电缆载流量的影响。通过实例仿真得出不同影响因素对电缆温度场分布的影响规律,并验证了该模型的准确性和可靠性。     

变电站电缆通道多参量采集和预警技术研究

针对变电站电缆通道数量的不断增加,电缆分布众多,某条线路的故障会带来极大的安全隐患。文中提出一种变电站电缆通道多参量采集和预警系统的设计方案,重点研究电力电缆的温度场和载流量。通过有限元分析软件,建立了10 kV单芯电缆四回路标准敷设电缆沟的几何模型,并采用割线法计算稳态载流量。通过实验分析了不同工况下的温度场和载流量。结果表明,对于在线电缆温度监测,只需要对温度最高的电缆进行监测,电缆铺设密度过高会导致电缆的载流量下降。该研究为中国变电站电缆通道多参量采集和预警技术的发展提供一定的参考和借鉴。     

翅片管外有机工质TFE凝结换热特性研究

翅片管外有机工质换热特性（凝结换热系数及液膜热阻）影响冷凝器的换热性能。理论模型基于努谢尔修正膜理论,为提高计算精度,将翅片管沿管周向划分有限个微元角,建立各个微元角内翅片侧壁和翅片间基管处的层流膜状凝结换热模型,迭代求解各个微元角内的壁面温度,根据各微元角壁面与饱和蒸汽温差,推导翅壁面及翅间基管上的液膜热阻和换热量,最后求解管子平均换热系数。管壁温度随圆周角θ增大而减小;翅壁及基管上液膜热阻随圆周角θ增大而增大;基管上液膜热阻大于壁面上液膜热阻。与实验值比较,理论模型计算精度高于积分解法计算值。     

A Fourier transform technique for calculating cable and pipetemperatures for periodic and transient conditions

An underground pipe-type cable system is represented by a thermal impedance network. A ladder network of resistances/capacitances represents the cable out to the outer surface of the pipe. The earth, adjacent pipe-type cables, and cable images are modeled by a frequency dependent thermal impedance found by solving the heat transfer differential equation. The heat input to the system is conductor I² R loss. The heat input can be a periodic signal or a transient of up to 300 h. A fast Fourier transform (FFT) is used to obtain heat input in the frequency domain. The frequency domain thermal input at the conductor is divided by the thermal admittance seen by the conductor and an inverse FFT is used to obtain conductor temperature as a function of time. A similar procedure obtains shield and pipe temperature. Iteration is used to model conductor electrical resistance change with temperature. The ambient temperature and temperature due to dielectric loss is added in to obtain final values