电力电缆安全监测中温度场和电场数值关系分析

首先采用有限元法分别计算了8.7/15 kV YJV 1×400 mm2直埋式电缆的温度场以及电场分布,在此基础上分析了二者之间的数值关系。计算结果表明电缆的温度场与电场之间呈近似的线性关系。从而在实际工程中,可以通过在线监测电缆的温度场分布,首先可以推算其负荷,对电缆负荷进行监控。并根据电缆电场与温度场之间的线性关系,推算其电场分布,得出电缆绝缘介质内的电场分布规律,判断内部电场是否超过安全限值,可以更好地监测电缆的绝缘状态,确保电缆的安全运行。     

电力电缆安全监测中温度场和电场数值关系分析

首先采用有限元法分别计算了8.7/15 kV YJV 1×400 mm2直埋式电缆的温度场以及电场分布,在此基础上分析了二者之间的数值关系.计算结果表明电缆的温度场与电场之间呈近似的线性关系.从而在实际工程中,可以通过在线监测电缆的温度场分布,首先可以推算其负荷,对电缆负荷进行监控.并根据电缆电场与温度场之间的线性关系,推算其电场分布,得出电缆绝缘介质内的电场分布规律,判断内部电场是否超过安全限值,可以更好地监测电缆的绝缘状态,确保电缆的安全运行.     

电动汽车动力电源系统低温加热策略研究

电动汽车动力电源系统在低温环境下工作,需通过外部加热的方式改善动力电池的低温充放电性能。在目前电动汽车行业内,动力电池系统采用的加热方式有很多种,主要介绍了一种利用PTC加热技术,通过改进电路设计和优化热管理控制方法,进一步提升PTC的加热效果,充分发挥动力电源系统的低温充放电性能,对电动汽车动力电源系统热管理发展具有巨大的推动作用。     

一种屏蔽电动机的三维温度场及影响因素研究

为了保证屏蔽电机能够长期稳定的安全运行,进行精细化、数值化热计算是非常必要的。为使换热器热计算与屏蔽电机温度场计算工况对应,首先针对外置换热器进行热平衡及传热计算,得到电机内、外部冷却进水的温度,作为屏蔽电机内三维温度场计算的边界条件,然后,建立电机三维物理模型,选取内部湍流流动及传热的数学控制方程及模型,按照实际给出边界条件,采用基于计算流体力学(CFD)原理的有限体积法进行求解,得到温度分布特征,分析了相关因素对温度场影响。结果表明,定子两端部铜绕组中的热量主要通过导热经铁心传至内外冷却水,增大铁心材料轴径向导热系数有利于降低峰值温度。所得结论为屏蔽电机冷却计算及设计提供参考。     

Two dimensional modelling of three core cable transient temperaturerise

A study of the transient temperature rise of a three-core cable is described. A literature search was unable to uncover any reference on this topic since a paper by F.O. Wollaston (Trans. AIEE, vol.68, pt.11, p.1284-97, 1949). Results from a computer program that models the two-dimensional heat flow are compared with those obtained using the normally applied one-dimensional model. The modeling technique is an alternative to the finite-difference and finite-element methods. It develops the concept of a thermal resistance/capacitance analog, as can be done using the finite-difference method, but does so more directly without the need to use the partial-differential equation. In addition, it provides the flexibility of the finite-element method when modeling a complex geometry and material combination, such as that found in a three-core cable, without the complexity of its mathematics     

A three-dimensional temperature field calculation for a transformer-type heating element

A mathematical model for calculating the temperature field of a transformer-type heating element with a spatial pole core using the finite element method is described. A computer simulation program of the three-dimensional temperature field is developed, and calculation results for a transformer of 25-kW capacity are given.     

Simulation of electric resistance furnace operation by means of numerical modelling

Contents A method of analysing thermal processes in electric resistance furnace, using the numerical technique and the one-dimensional, multidirectional, nonlinear model is presented. The way of calculation is shown on examples of real industrial furnaces. The analysis of heating-up with constant power and with constant temperatur speed are shown. The examination of model imperfection is carried out, including one-dimension representation, time and space discretization, non-constancy of thermophysical parameters and the effect of ambience. Practical aspects of method application are metioned.

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Simulation der Wärmeprozesse in Widerstandsöfen mittels eines numerischen Modells-Möglichkeiten und Grenzen

Übersicht Die dargestellte Methode zur Analyse der Wärmeprozesse in Widerstandsöfen umfaßt die numerische Behandlung und das eindimensionale nichtlineare Mehrwegmodell. Die Berechnung wird am Beispiel realer Industrieöfen erklärt. Eine Analyse der Anheizung mit konstanter Leistung und mit konstanter Temperaturgeschwindigkeit wird durchgeführt. Die Fehlerquellen des Modells werden quantitativ untersucht, und zwar die eindimensionale Darstellung, Zeit- und Raumdiskretisation, nichtkonstante Wärmeparameter und der Einfluß der Umgebung. Praktische Ausblicke der Methodenanwendung werden erwähnt.

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List of symbols B speed of temperature rising - c specific heat - C _c radiation constant of the black body - d thickness - E energy - G conductance - J node point - m mass - P power - S surface - T absolute temperature, temperature - TN new temperature - t time - x space coordinate - overall heat transfer coefficient - emissivity - thermal conductivity - mass density - temperature - aperature factor Indices ak accumulated - a outer, ambient - c convection - g loss - gr heater - i, j order numbers - n normal - otv opening - p floor, surface - r radiation - rad radiation through openings - s charge, overall - sp surface - sr average - st steady state - u inner - z wall - zad reference     

Stationary thermal field in a long duct of an electrical heating system

Contents The subject of this work is the analysis of a stationary thermal field in a long duct of an electrical floor heating system. Parallel sectors of the heating cable are modelled by heat sources of the emitted power linear density. The resultant thermal field is described by a partial differential equation of the elliptic type with boundary conditions of the second and third kind. The problem is solved by the method of eigenfunctions. The results are reduced to a dimensionless form and numerically processed. The field distributions obtained are presented in graphical form, with the number of sectors of the heating cable in the duct being changed.

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Das stationäre Temperaturfeld im langen Kanal einer elektrischen Fußbodenheizung

Übersicht Der Artikel analysiert das stationäre Temperaturfeld im langen Kanal einer elektrischen Heizung. Parallele Kabelstrecken wurden durch Wärmequellen ersertzt. Das Temperaturfeld wird mit Hilfe der partiellen Differentialgleichung des elliptischen Typs dargestellt. Dieses Problem hat man durch die Eigenfunktion gelöst. Die Ergebnisse wurden in eine dimensionslose Form umgewandelt und numerisch bearbeitet. Die Feldverteilungen wurden graphisch dargestellt, wobei die Anzahl der Kabelabschnitte verändert wird.

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List of symbols A dimensionless constant, determined by (6b) - 2a, 2b dimensions of the cross-section of the duct (Fig. 1.) - B _mm coefficient of the series (5), determined by (8) - c _k relation of linear density of the power of heaters; thek-th to the first (q _k /q ₁) - K number of heaters - k index of thek-th heater (k=1,2,...,K) - L(x/2b, y/2b) total dimensionless thermal field in the duct - L _k (x/2b, y/2b) dimensionless component of thermal field caused by thek-th heater (with the others turned off) - q _k linear density of the power of thek-th heater [W/m] (k=1,2,...,K) - S cross-section of the duct - T=T(x, y) total temperature field in the duct - T _k (x, y) component of the temperature field in the duct caused by thek-th heater (with the others turned off) - T ₀ temperature of air far from the top surface of the duct - v _k (x, y)=T _k (x, y)–T ₀ k-th component of an increase in the thermal field in the duct over the valueT ₀, caused by thek-th heater (with the others turned off) - (x, y) Cartesian coordinates of a point in the duct - (x _k ,y _k ) coordinates of the position of thek-th sector of the heating cable, averaging coefficient of heat transfer to air (sum of the radiation and convection coefficients) [W/(m ² K)] - averaging coeffiecient of heat transfer to air (sum of the radiation and convection coefficeints) [W/(m ² K)], - _n successive positive roots of (6a), (6b) - (x–x _k ), (y–y _k) Dirac's deltas shifted tox _k andy _k respectively - _m0 Kronecker's symbol - averaging heat conductivity of micro-reinforced concrete [W/(mk)]     

汽车动力电池低温加热方法研究

为满足汽车动力电池的低温使用要求,根据传热学的原理,建立了动力电池的低温加热模型,并利用该模型设计了低温加热方案,通过对比分析两种不同的低温加热器的优缺点,选用了电热膜加热器方法。仿真计算和实验结果表明,设计的电热膜加热器具有良好的低温加热效果,不会影响动力电池的散热,而且具有良好的常温保持性能。     

冲击电压下电缆终端的非线性电场数值分析

基于后退欧拉法和变分原理推导了非线性电场的暂态有限元方程。利用暂态有限元方法分析了含不同应力控制管时的电缆终端冲击电压下的电场分布。分析结果表明,在冲击电压下电缆终端采用由电容性和非线性电阻性材料复合绝缘结构的应力控制管时,电场分布最为均匀。     

快热式电热水龙头的水位设计和水温设计

正常工作状态下电热管、热保护器等关键件损坏和按标准进行检测出水温度过高是目前快热式电热水龙头产品较严重且较难整改的质量问题.本文介绍了通过水位设计和水温设计来解决上述问题的方法.     

回转式空气预热器温度场三维数值模拟

烟气经选择性催化还原（SCR）脱硝后,产生的硫酸氢铵会造成空气预热器（空预器）冷端蓄热元件腐蚀和堵塞。将三分仓回转式空预器转子看成多孔介质,建立了非热平衡模型,模拟得出某600 MW机组空预器工质和受热面三维温度分布,分析了烟风出口温度和受热面转子温度沿旋转方向的变化规律。结果表明:烟气沿流动方向温度逐渐降低,空气沿流动方向温度逐渐升高,出口温度沿旋转方向几乎呈线性关系,且由于分仓的存在,沿旋转方向各个分仓的交界面上温度是不连续的;蓄热元件温度从热端到冷端逐渐降低,沿旋转方向呈先增后减的趋势;低温腐蚀危险区域主要集中在冷段,硫酸氢铵沉积危险区域主要集中在冷段和热段交界处。     

大气电场仪观测资料数字序列的时间特征分析

根据某大气电场仪的数据传输方式,按照数据包接收端的计算机时间和数据包顺序号,利用最小二乘法对观测数据做分段直线拟合、建立分段线性关系,求得数据包平均时间间隔和数据包参考时间,进而在无线通讯网络堵塞情况下对被延时的数据包进行到达时间的修正、计算出每个场强值的观测时间,从而达到提高数据序列的可读性、提高宝贵的实测资料的利用价值之目的。此方法成功地恢复了该类型大气电场仪组网观测所获得的一批观测资料的观测时间,为这些资料的专业分析和应用提供了保障。     

Numerical modelling of the stationary Maxwell–Lorentz system in technical devices

The particle-in-cell method is coupled with boundary-fitted co-ordinates in order to model the stationary Maxwell–Lorentz problem in technical devices. New numerical algorithms describing the transition between the grid model and the mesh-free model are developed and the existing techniques of finite difference schemes for equidistant grids are extended to non-equidistant, arbitrarily shaped, convex four-point meshes. The modelling process is described, and both the numerical approximation and the algorithms are discussed. Applications in different technical devices show the flexibility of the method.     

供热电锅炉的PLC控制系统优化设计

对电加热锅炉自动控制系统进行了整体优化设计,根据系统的工作流程,使用西门子S7-200 PLC作为控制核心.采用4组电加热管自动投切的控制方式,保证了系统的可靠性与经济性,并给出了基本的硬件配置和编程原理.     

光纤智能测温度系统在电网上的运用

基于布里渊散射的光纤光栅传感技术,利用返回激光功率"过零点"的测量方法,设计出一个可用于电网温度监测的准分布式光纤智能测温度系统.在全长100 m的16条光纤通道上安装48个监测点,实现了对每个监测点的实时温度监测,在室温下的监测精度为±2 ℃.理论上,监测的温度范围为250 ℃.     

Analytical formula of induced electric fields in a spherical conductor by an ELF dipole magnetic field source

An analytical formula of induced electric field E in a spherical conductor by an ELF dipole magnetic field source is mathematically derived in vector form based on the equivalent mutlipole moment method with reexpansion technique (RE‐EMMM), where M _‖ and are parallel and perpendicular components of M , respectively. The validity of the formula is confirmed in the following three ways: (i) the derivation of the formula from the Sarvas equation with the reciprocity theorem derived by Eaton; (ii) the convergence of the formula to that of homogeneous magnetic field when M _‖ is located at the infinite distance; (iii) comparison of the analytical solutions with numerical solutions by RE‐EMMM. Furthermore, a formula for the trajectory, which satisfies E = 0 , is derived for the field by M _‖. © 2008 Wiley Periodicals, Inc. Electr Eng Jpn, 166(3): 8– 17, 2009; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20739     

Mathematical modelling of three-phase electrode salt-bath furnace with the two-dimensional electric field

Contents After a short historical survey of the attempts to solve the problem of designing and determining the dimensions of a three-phase electrode salt-bath furnace, the authors apply the theory of the three-phase transmission line with uniformly distributed parameters to the phenomena in the electrode furnace. Taking all necessary boundary conditions and permissible simplifications, formulae for most widely sprcad types of the furnaces are derived, which allow the calculation of input admittance and input power of the furnace, as well as other important electric quantities.

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Ein mathematisches Modell des dreiphasigen Elektroden-Salzbadofens mit zweidimensionalem elektrischen Feld

Übersicht Nach einer kurzen historischen Übersicht der Versuche einen dreiphasigen Elektroden-Salzbadofen zu projektieren und seine Abmessungen zu berechnen, wenden die Verfasser die Theorie der dreiphasigen Übertragungsleitung mit gleichmäßig verteilten Parametern auf die Erscheinungen im Elektroden-Salzbad-Ofen an. Mit Hilfe notwendiger Randbedingungen und zulässigen Vernachlässigungen werden die Formeln für die am meisten verbeiteten Ofentypen hergeleitet, die die Berechnung der Eingangsadmittanz und der Anschlußleistung des Ofens wie auch andere wichtige elektrische Größen ermöglichen.