Electrical and thermal analysis of polymer insulator undercontaminated surface conditions

Electrical and thermal analysis of a 15 kV silicone rubber distribution insulator was made under contaminated surface conditions. The electric field on the insulator surface and in the surrounding area was determined by using the finite element method technique, while the temperature distribution along the insulator surface was calculated by solving the heat transfer differential equation numerically. A special mathematical treatment was used to reduce the heat transfer equation into a 1-dimensional problem. The effects of initial surface contamination upon the features of electric field was studied. The dependence of the change in insulator surface temperature as a result of leakage current flowing over the contaminated surface on the physical parameters involved in the heat conduction process was studied and is presented in detail     

局部对流换热对输电线路高频激励融冰的影响

在覆冰导线高频激励融冰温度场的分析与计算中,局部对流换热对温度场及高频激励融冰模型有很大影响。对此,文中分析了高频融冰过程中的热量损失和对流换热的影响因素,通过Ansys有限元软件对高频激励融冰模型的电磁场和热分析与计算,揭示了局部对流换热对高频融冰模型温度场及其迎风侧和背风侧的影响,表明了局部对流换热使导线背风侧覆冰先融化脱落,迎风侧覆冰后融化脱落。覆冰导线外表面的温度随对流换热的系数增大而下降,下降速度随对流换热系数增大而减缓。该研究成果有利于进一步改进和优化高频激励融冰计算模型。     

对流换热对覆冰导线高频融冰温度分布的影响

根据流体力学的基本原理,应用有限元分析软件ANSYS建立覆冰导线高频融冰时的外流场模型,得到覆冰导线高频融冰时的周围空气流场、压力场分布规律及覆冰导线表面对流换热差异性。分析了高频融冰过程中的热量损失和对流换热的影响因素,通过电磁与热分析,揭示了高频激励融冰过程呈不均匀非对称融冰规律,覆冰导线迎风侧压力大、温度低,背风侧压力小、温度高,表明不均匀对流换热使覆冰导线背风侧先融化,迎风侧后融化。在环境温度和覆冰厚度一定的条件下,覆冰导线外表面温度随对流换热系数的增大而降低。     

横向磁场电励磁磁通切换磁悬浮直线电机温度场有限元分析

研究用于轨道交通的横向磁场电励磁磁通切换磁悬浮直线电机特殊结构下的温升问题,设计冷却系统以保证电机正常运行。分析电机的结构和运行原理,建立了三维稳态温度场数学模型,并推导出边界条件方程。考虑电机各部分热交换的情况,确定各材料的导热系数以及电机不同部分的对流换热系数。通过有限元方法计算出电机的铜损耗与铁损耗,并求出相应的生成热。利用三维有限元法对电机不同工况下的温度场进行计算,得到了电机铁心、电枢、励磁绕组的温度场分布情况。最后,设计冷却系统,比较自然风冷和强制水冷的温度分布,证明该冷却系统装置的可行性和合理性。     

组合式相变材料吸热器热性能研究

针对NASA 2kW高温相变吸热器采用单-熔点的相变材料出现的问题，提出了由3种相变温度不同的相变材料组成的组合PCM吸热器模型，建立了相应的物理模型，给出了数值求解方法，计算了换热管最大温度、工质出口温度、换热管总PCM熔化率等结果。并与单一PCM换热管吸热器进行了比较分析，说明采用组合PCM换热管可以很好地提高吸热器的性能，减少工质温度被动、减少吸热器质量。计算结果可用于指导吸热器的设计。     

电机三维温度场的综合分析

运用稳定导热问题的有限差分法分析电机三维温度场,对电机内的对流换热系数采用ｈ＝ ｃ　ｖ~ｎ的计算公式,引入气体热流的概念,对电机温度场与电机内空气温度场使用耦合边界条件,实现了两者的同时迭代求解。     

均匀高压电场强化圆管和套管内油的层流强制对流换热的综合效应

以 1 5号机油为实验工质 ,对水平光滑圆管和套管管内层流流动换热进行了直流高压电场强化实验研究。以实验方法调查了其换热系数强化率与外加电场强度、热通量及流动速度、油温、管型等因素的相关性。实验证实了外加直流高压电场能对管内层流强制对流换热起着很好的强化作用。在相同传热面积及相同泵功的条件下 ,综合换热性能有大幅度增加。     

基于链式的爆炸气流场耦合电弧动态模型

为研究大电场条件下有效熄灭电弧的优良方法,在开放空间下,考虑爆炸产生的冲击波及强烈气流耦合电磁场等因素的影响,基于电弧链式思想和经典激波理论分析电弧在爆炸气流影响下的受力情况,推导出电弧运动速度控制方程。在此基础上,结合能量平衡方程及热交换原理,建立耦合场的电弧模型。通过有限差分法求解模型,分析气流耦合电磁场下电弧熄灭的运动过程和物理特性变化,并得出电弧状态相关参数(温度、电导率等)和熄灭时间的特性。试验结果表明电弧熄灭效果具有工程应用价值。     

A model for calculating composition and density of the core melt in the water-moderated water-cooled reactor in case of severe accident

Thermochemical behavior of the core melt in the VVER-type reactor at severe accident is discussed. Experimental information gained made it possible to construct a thermodynamic model of the O-U-Zr-Fe system. The model describes the immiscibility of the oxide and metal phases of the core melt and makes it possible to estimate their densities. Parameters of the model were obtained by comparison with diagrams of binary and ternary subsystems, as well as with results of the MASCA experiment. Additional verification calculations show good agreement of the theory with experiment. In particular, parametric calculations showed that there is a wide enough region of the core melt parameters at which densities of the oxide and metal phases are comparable in values, but this fact does not rule out the probability of stratification with upper position of the oxide layer. In its simplified formulation the model has been incorporated into the HEFEST code. Results are reported for calculations of heat transfer in the stratified core melt in the reactor vessel for two different cases of relative location of the melt layers.     

计算Scott牵引变压器内部温升的热路模型法

牵引变压器的绝缘寿命很大程度上取决于绕组热点温度,研究其内部温升具有重要意义。为此,针对Scott牵引变压器特殊的绕组连接、铁心结构和电气特性,利用热传输原理分析了其内部热量的产生和传输过程;参考电路原理建立了Scott牵引变压器内部热路模型;参照基尔霍夫定理推导了温升的计算式,从而建立了Scott牵引变压器的热路温升计算模型和简化的热路温升计算模型;采用两种热路温升计算模型和IEC温升计算法仿真了同一负荷下的Scott牵引变压器,仿真结果说明了模型的有效性。     

考虑变工况特性的微能源系统优化规划：(一)基本模型和分析

微能源系统是能源互联网发展应用的重要形式之一。微能源系统是一个多输入多输出系统,各类能源转换设备和存储设备构成系统输入和输出的耦合关系。各设备通常具有非线性工作特征,使其运行特性与设计点发生偏移。针对微能源系统输入/输出的非线性关系,考虑储能的接入,建立微能网变工况静态耦合模型和储能状态转移模型,通过输入能源的统一折合,定义系统综合能源消耗,并提出依据微增率安排能源转换设备出力的策略。最后,以一个包含光伏、配电变压器、天然气热电联供、热泵、电池储能、蓄热式电锅炉的系统对所建立模型进行了应用和验证。提出的考虑微能源系统变工况特性的通用模型,是微能源系统优化设计和运行的基础。     

基于热积累的电动机过载保护数学模型

过载保护技术是低压电器智能化技术的重要组成部分,是保证电动机、配电线路安全运行的重要技术。以热保护为研究对象,充分考虑电机的热积累现象,通过求解热甲衡微分方程的方法,给出了新的电动机过载保护判据。与常用反时限保护特性相比较,此保护模型更符合负载的实际运行规律及保护要求。     

基于电接触元件暂态热路建模的接触电阻测量研究

目前,接触电阻的检测主要是电压电流法或电桥法,其不足是仅适于离线应用。提出了一种在线式的接触电阻间接测量新方法。首先在建立电接触元件的理论物理模型和径向暂态热路分析模型的基础上,推导出热路响应方程;然后再在建立元件轴向热传导数值分析模型的基础上,最终推导出计及温度和电流的接触电阻曲线关系,提出通过曲线的时间常数计算电接触元件的接触电阻。大量的理论分析、计算与有限元分析ANSYS仿真表明,所研究的测量方法可以准确求取接触电阻的值,为电气设备的在线监测和热缺陷分析提供了理论依据。     

An Energy-Efficient Electric Plant for Hot Steam and Water Supply of Agricultural Enterprises

The efficiency of electric energy use in the thermal technological processes of agricultural production can be significantly increased by using it during a period of reduced rate. The design features of an energy-efficient electric storage unit for steam and hot water supply of the agricultural facilities are considered. The electric plant includes a storage water heater, steam generator, section of steam superheating to a temperature of 140°C, control cabinet, and stop and safety valves. When heating the heat medium in all units of the plant, an indirect electric heating method was applied. A method of calculation of the electrical, thermal energy, and structural parameters is proposed. The results of physical modeling of the processes of heat transfer between the electric heater and heat medium are presented, and they are described mathematically. The dependence of the heat transfer coefficient on the specific surface power of the heaters when water boils in a large volume for the installed structure of the electric steam generator is obtained. The dynamics of the convective heat transfer between the electric heater and steal flow is studied. The economic efficiency of use of the storage electric plant is demonstrated, and it is shown in practical use.     

A Three-Dimensional Mathematical Model for Flow and Heat Transfer in Electrical Glass Furnaces

A three-dimensional mathematical model was developed for calculating joule heat release, glass flow, and heat transfer in electric glass furnaces. The model developed here allows for multiple electrodes, multiphase firing, and for the feeding and withdrawal of molten glass. The model is fairly general with respect to the arrangement of the electrodes, the firing pattern, and the choice of the boundary conditions, and it allows for the temperature dependence of the glass properties. The model was used to calculate electric potential, rate of heat release, flow pattern, and temperature distribution in the melting of flint and amber glasses in an all-electric melter with side-entering electrodes. The calculations were performed for the industrial conditions of pull, power, and the electric firing scheme. The bulk glass temperature was found to be very uniform with large temperature gradients near the boundaries. The calculated flow pattern was, in general, quite complex with several circulation loops. The temperature and the maximum velocity for the amber glass were found to be higher than the corresponding values for flint glass.     

电—热综合能源系统中能量的整体输运模型

促进可再生能源消纳、提高能源综合利用效率是电力和热力等能源系统可持续发展的重要途径。针对电力和热力两种异质能源系统在传统研究对象和分析方法上的差异性,引入理论,结合热电比拟方法,从热量输运的驱动力和阻抗的角度揭示了热系统中基本元件的本构关系,并从能量流的视角对其重新建模,结合热系统的拓扑结构,提出热系统的能量流模型来描述系统中热量的整体输运规律。在此基础上,同时考虑电—热综合能源系统中的能量平衡特性和热量输运的不可逆性,提出了电—热综合能源系统的整体能量流模型,统一了电能传输和热能输运的研究视角,揭示了系统中能量的整体输运规律。最后,针对一个简单的电—热综合能源系统,以最小化系统总煤耗为目标,应用能量流和互为边界的方法分别预测了风电出力情况,结果表明能量流法预测的风电出力更准确,从而验证了能量流法的可行性和必要性。     

空气开关电弧仿真技术及其应用的研究

通过仿真技术研究了空气开关电器中空气电弧。建立了电弧磁流体动力学（MHD）模型,并求解模型控制方程,分析了电弧运动、触头打开、电弧转移等过程。该项研究可为开关电器产品的优化设计提供理论参考。     

27.5kV GIS母线室三维温度场的数值计算

基于热传导微分方程、流体运动控制方程及辐射换热方程,建立了传导、对流和辐射换热相互耦合的数学模型,并采用壁函数方法处理固体与流体界面的对流换热问题,对27.5kV GIS(gas-insulated switchgear)开关柜母线室的三维温度场和气流场进行了数值计算与分析。仿真中采用了六面体网格剖分,通过有限容积法对方程进行离散求解,得到了母线室内的三维温度场与气流场的分布。计算结果表明,三工位隔离开关为温度最高部位,气体的对流使得母线室内温度趋于均匀并使载流回路的散热效果得到了加强。进行了相关的温升实验,温度的数值计算结果与实验结果吻合,表明了计算方法的正确性。     

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.     

管内变物性流体减速时对流换热实验结果的数值模拟

用一组封闭的迟豫方程来计算湍流应力τT 和湍流热流密度 qT,从而建立起湍流迁移模型 ,此模型与大量实验结果相吻合 ,具有普适性。采用此湍流迁移模型对圆管内变物性流体在减速流时并考虑非定常流的影响 ,对热交换过程进行数值模拟研究。与实验相比较 ,得到较一致的结果。表明 :同时考虑变物性和非定常性的影响 ,使得数值模拟和实验的比较具有实际意义