电气化铁路27.5kV单相单芯交联聚乙烯电缆载流量计算

电气化铁路单相供电电缆是电气化铁路运行的关键组成部分,为获得铁路专用27.5kV单相单芯交联聚乙烯电缆的载流量,通过仿真计算的方法进行了研究。首先对电缆的运行情况进行分析,用有限元法对比计算了单相供电与三相供电条件下电缆金属护套涡流与环流损耗。在对电缆的环流损耗与涡流损耗计算的过程中,通过对计算单元自由度的修改与温度场的耦合,为电气化铁路单相供电电缆载流量计算建立更为精确的计算模型。在该模型的基础上,根据铁路电缆实际敷设环境,分析了不同接地方式、线芯间距、回路数量、媒质热阻、环境温度下电缆载流量的变化。结果表明:双端接地方式下铁路单相供电电缆金属护套层环流损耗较三相供电提高约75%,单端接地方式下相位影响不明显;电缆温升受相邻电缆间距、周围媒质热阻及温度影响较大;回路数增多,受临近电缆的影响,中间电缆的温升将导致电缆整体载流量下降。     

35kV单芯电缆金属屏蔽层感应电压计算及接地处理方案

通过对单芯电缆金属屏蔽层感应电压的计算得出,在三相回路系统中,当三相平衡负载情况下以对称敷设(等边三角形敷设)时,电缆金属屏蔽层上的感应电压最小且相等.提出了多点接地的单芯电缆金属屏蔽层感应电压处理方案.该方案是中间直接接地、两端保护器接地方式的进一步发展,两端通过端保护器接地,而中间在一定范围内进行直接接地.采用该接...     

多种敷设方式下集群电缆的直流载流量仿真研究北大核心CSCD

为了研究集群电缆敷设方式、回路间距、回路数以及排列方式对交流集群电缆直流载流量的影响,以10 kV交流配电网中广泛使用的三芯交联聚乙烯(XLPE)电缆为例,通过有限元仿真软件建立集群电缆的温度场和流场耦合仿真模型,得到了直埋敷设、排管敷设和沟槽敷设下集群电缆以双极式直流拓扑结构运行时的直流载流量、温度分布和流场分布。结果表明:随着回路间距和回路数的增大,集群电缆载流量的变化速率逐渐减小。直埋敷设下集群电缆之间的热场相互作用最大,而沟槽敷设下集群电缆之间的热场相互作用最小。增大集群电缆水平间距来提高直流载流量的效果要优于增大垂直间距。随着集群电缆距沟槽壁的水平距离增大,直流载流量呈现缓慢的下降趋势。研究结果可为多回路10 kV交流XLPE电缆的直流改造工程提供理论依据。     

多回路电缆布置优化的研究

为降低城市多回路电缆平行敷设工程的造价,可采用改变各回路电缆相序的方式来降低电缆金属护层上的感应电压。为此,通过感应电压计算和矢量分析法,分析了多回路高压电缆线路变化布置方式对电缆金属护层感应电压的影响,结果表明:减小同一回路三相电缆的相间距离或增大不同回路电缆之间的回路距离,可以降低多回路平行敷设电缆金属护层的感应电压值;多回路电缆线路的布置中,不同的相序排列组合对电缆金属护层的感应电压值有明显影响。因此,在敷设多回路电缆时,应兼顾有利于电缆散热和降低电缆金属护层感应电压值两方面,确定电缆之间的距离。     

高压电力电缆金属屏蔽层接地问题分析

随着城市高速发展,110 kV以下高压电缆在城市供配网中被大量用于地下电力电缆线路。当单芯电缆线芯有电流流通时,金属屏蔽层上会有磁链,金属屏蔽层两端就会出现感应电势。高压电力电缆金属屏蔽层接地可防止人身触电,确保电力系统正常运行,保护线路和电气设备免遭损坏,但高压电力电缆金属屏蔽层接地方式一直没有统一的规定,高压电力电缆金属屏蔽层因接地不当而引发的电力事故给企业造成了巨大的经济损失。通过对不同长度下电缆金属屏蔽层接地问题分析,得出不同长度下电缆金属屏蔽层的推荐接地方式,为现场接地提供相应指导。     

单芯电缆接地方式选择以及预防金属屏蔽层多点接地的办法

通过对35 kV单芯电缆金属屏蔽层感应电压的理论计算与现场实测,提出了大型企业35 kV单芯电缆金属屏蔽层接地方式,结合现场运行经验提出了应对单芯电缆金属屏蔽层发生多点接地的措施。     

高压交联聚乙烯绝缘电缆的选择

本文对高压交联聚乙烯绝缘电力电缆的有关问题进行了讨论 ,对电缆导体、金属屏蔽层或金属护套、外护套等选择进行了比较 ,也对金属屏蔽层的接地和敷设方式进行了分析和讨论。     

单芯交联聚乙烯绝缘电缆金属屏蔽层的接地

对于单芯交联聚乙烯绝缘电缆，当其导体中流过交流电流时，它所产生的磁通的一部分将与金属屏蔽层铰链，使得金属屏蔽层产生感应电势，其大小与电缆的排列方式（三角形或扁平形）、电缆中心轴间距、电缆金属屏蔽层平均直径以及换位（正常换位或不换位）等情况有关，与电缆的长度和导线电流大小的乘积成正比。在电缆长度和导线电流较大的情况下，感应电势可能达到很大的数值。尤其当系统发生短路事故时，导线电流可能达到其正常电流的几倍甚至几十倍，或当线路遭受操作过电压。雷击过电压时，金属屏蔽层都会感应出很高的感应电势，达到危及人…     

高压交联聚乙烯电力电缆的选择

主要从电缆导体、金属护套、外护套等方面对高压XLPE电力电缆的选择作了讨论，同时对XLPE电力电缆金属屏蔽层的接地方式及电缆敷设方式进行了分析。     

高压交联聚乙烯绝缘电缆的选择

本文对高压史联聚乙烯绝缘电力电缆的有关问题进行了讨论，对电缆导体、金属屏蔽层或金属护套、外护套等选择进行了比较，也对金属屏蔽层的接地和敷设方式进行了分析和讨论。     

Nonlinear-coupled electric-thermal modeling of underground cable systems

An original nonlinear-coupled electric-thermal model of underground cables with the solid sheaths is proposed. The model deals with the numerical evaluation of losses, heating, and ampacity. The computation of the current dependent losses is undertaken by means of the filament method, where conductors and sheaths are represented by a number of smaller subconductors or filaments. Furthermore, heat-transfer phenomena through an "infinite" domain beneath the soil surface are modeled combining the finite and the mapped infinite elements, respectively. The corresponding finite-element meshes are generated by the advancing front method. The numerical results presented throughout this work suggest that the International Electrotechnical Commission relation concerning the external thermal resistance for touching cables, placed in flat formation, having appreciable sheath losses, should be re-examined.     

变压器线圈涡流损耗的解析算法

本文提出了变压器线圈涡流损耗的解析算法,给出了变压器窗口漏磁场及导体涡流损耗的解析公式,讨论了双重富氏级数收敛项数的选择,并以两台具有短路损耗实测值的变压器为例进行了计算、对比.     

大截面电力电缆固定金具三维涡流场有限元分析

文中建立了大截面电缆固定金具的三维涡流场数学模型,考虑初始条件和边界条件,利用有限元法分别研究了缆芯电流、金具材料电导率以及金具厚度对金具涡流损耗的影响。计算结果表明,金具涡流损耗均随电流、电导率以及厚度的增加而增大。当电流较大时,金具涡流损耗变化较快;当电导率较大时,反而金具涡流损耗变化趋于平缓;金具涡流损耗随厚度的变化呈线性关系。文中提出选用不锈钢作为金具材料可以有效地降低金具中所产生的涡流损耗。     

PWM逆变器供电引起的轴向磁通非晶电机谐波损耗的解析计算

非晶合金材料具有出色的低损耗特性,适于用作高频电机的铁心,但PWM逆变器供电会导致高频电机谐波损耗严重增加。在电机初始设计阶段,快速准确计算出谐波损耗是轴向磁通非晶合金永磁电机设计及优化的关键。针对3D时步有限元计算耗时长的问题,改进现有多环等效模型的计算方法,推导了考虑PWM逆变器供电高次谐波电流影响的气隙磁通密度解析计算方法,并在此基础上推导了定子铁心损耗及考虑涡流反作用影响的转子涡流损耗的解析计算方法。将谐波损耗的解析计算值与样机实验值以及3D有限元计算值进行对比,结果显示谐波损耗的平均计算误差仅为9.69%,解析模型具有较高的计算精度。     

Theoretical investigation on skin effect factor of conductor in power cables

This paper describes a newly derived theoretical equation on the skin effect factor of power cables, and its application to large‐size OF and XLPE cables with segmental conductors, including insulated wires. The skin effect factors calculated with the new equation were fit very well to measurements in a wide range of conductor sizes. In the new equation, the important factor which characterizes the skin effect of segmental conductors is the “equivalent conductivity ratio” v defined by the ratio of longitudinal conductivity in axial direction of conductor to conductivity of conductor wires. Since the obtained ratio v in XLPE cable was three times greater than that in OF cable, the larger longitudinal eddy current passing from a wire to another increased the eddy current loss in conductor, which increased the conductor loss of XLPE cable. The new equation enables us to investigate quantitatively the dominant loss component affecting the skin effect factor. Then, the skin effect factors and coefficients for OF and XLPE cables were investigated with the new equation. It was revealed that the best number of separation, in which the skin effect reached a minimum, existed in OF and XLPE cables with segmental conductors. In addition, it was confirmed that the skin effect coefficients ks1 calculated with the new equation were very consistent with those used in JCS. © 2008 Wiley Periodicals, Inc. Electr Eng Jpn, 165(1): 18–34, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20576     

基于有限元法的高频变压器绕组损耗研究

变压器损耗是影响变压器运行性能的重要因素。在高频效应下,邻近效应与集肤效应会增加变压器绕组损耗。文章基于高频变压器绕组的三维模型,在考虑邻近效应与集肤效应的基础上,应用有限元法对变压器绕组中的涡流效应进行仿真计算。通过计算得出了改变绕组布局可以有减少绕组损耗的结论。并得到了不同绕组布局下,绕组损耗随频率、绕组厚度以及层间距的变化趋势。     

Calculation of conductor temperatures and ampacities of cablesystems using a generalized finite difference model

The objective of this study is the development of generalized two-dimensional finite-difference model (FDM) for the calculation of conductor temperatures and ampacities of a cable-system with separation between the cables ranging from direct contact to a finite distance. The heat-sources or sinks which are the conductors are represented in the model as a two-dimensional finite-difference thermal resistance mesh, which is solved by iteration using the digital computer. The effects on conductor temperature due to skin effect, eddy currents, and associated losses have also been included in the analysis for completeness     

Factors influencing ampacity and temperature of underground power cables

This paper presents the factors that influence ampacity and temperature rise of three-phase, single-core 33- and 500-kV XLPE underground cables (UGC) using CYMCAP software. These factors are conductor cross-sectional area, soil thermal resistivity, cable burial depth, cable separation, sheath bonding, bedding and backfill heights and thermal conductivities, nearby parallel heat source, formation of dry zone, loss tangent and segmented conductors. Results reveal that increasing the separation distance between phases gives higher ampacity, contrary to the burial depth. The rate of conductor temperature reduction due to the increase in the bedding thermal conductivity is more pronounced than that achieved by increasing backfill thermal conductivity. Furthermore, increasing the native thermal conductivity and/or the maximum conductor temperature increases the UGC ampacity and consequently increases the induced sheath voltage. Sheath losses are significant in transmission UGC where the load currents are always high. High conductor temperature and hence degradation rate is expected for UGC carrying currents of highly fluctuating loads. UGC must be derated as they age (increasing loss tangent), or when dry zones are formed around them, or when a nearby parallel heat source. Finally, it is found that the increase in the number of conductor segments nonlinearly increases the UGC ampacity.     

双回路电缆护套环流计算及影响因素分析

为分析电缆线路中的环流,推导了双回路敷设电缆护套环流的计算方程,并自行编制运算程序实现了计算机求解。结合某电力设计院两回路电缆的实际敷设及运行参数,计算了直线排列交叉互联情况下电缆护套中的环流,并对影响金属护套中环流值大小的相关因素作了简单分析,减小环流值的方法有增大接地电阻、使电缆紧密排列、保证电缆交叉互联段长度相等等。同时,提供了对应单回路敷设情况下的计算结果进行比较,结果表明计算护套环流时双回路不能以单回路情况简化。相关推导过程及程序设计思想可推广应用于双回路电缆的其它敷设形式或更高回路数的电缆线路。     

变频调速屏蔽电机仿真及其损耗计算

针对屏蔽电机的变频调速,在同步旋转坐标系上建立了屏蔽电机的数学模型,采用MATLAB软件中的Simulink工具对控制系统进行仿真,给出了仿真实验结果。当屏蔽电机采用变频器供电时,变频器输出的大量谐波必定会在屏蔽套内产生谐波涡流损耗。对此进行了谐波分析,计算出了屏蔽套的涡流损耗。