Optimum phase configurations for the minimization of the magnetic fields of underground cables

In this paper, underground cable arrangements of two, three and more three-phase systems are examined, which are constituted by single-core cables. Specifically, typical flat arrangements of cables are examined as well as a typical arrangement of cables installed inside a tunnel. Parametrical investigations are conducted in the phase configurations of the cables in order to reduce the magnetic flux density in the vicinity of the cables and to determine the configurations which produce the minimum maximum values of the magnetic field (optimum configurations). The optimum phase configurations are verified for various installation depths and various distances between the cables and between the three-phase systems. In arrangements of two three-phase systems, without involvement between the two systems, there are 36 possible phase configurations. Those configurations are categorised in groups of six configurations which produce the same magnetic field. In this way, six independent configuration groups arise. Respectively, in arrangements of three three-phase systems, there are 216 possible phase configurations from which 36 independent groups arise. For any number n of three-phase systems there are 6 ⁿ possible phase configurations from which 6 ^n-1 independent configuration groups arise. There is always one group of six phase configurations (optimum configurations) which cause the greatest reduction (drastic reduction) of the maximum value of the magnetic flux density.     

220kV高压单芯电力电缆金属护套环流分析

根据单芯XLPE电力电缆金属护套环流计算模型,编写C++程序,计算了交叉互联单元内三段电缆布置方式和段长不一致时的金属护套环流,并将计算结果与现场测试结果进行比较分析。根据计算和现场测试结果,一个交叉互联单元内三段电缆的段长和布置方式不一致对金属护套环流有影响,当电缆采用直角三角形和水平布置方式时影响尤为严重。为减小金属护套环流,高压单芯电缆应尽可能采用正三角形布置方式且保证三段电缆布置方式一致,段长尽量相等。     

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。     

排管电缆群布置方式的联合优化方法研究

电缆群不同的布置方式会影响其温度场的分布,进而对其载流量产生影响。文中以3×4排管敷设配电电缆群为对象,利用COMSOL和MATLAB建立电缆群温度场联合仿真模型,以等负荷电缆群中最热电缆线芯温度最低为依据优化多回路电缆群的布置。在多回路所有布置方式电缆群温度仿真计算的基础上,最终确定电缆群的最优布置方式以及新增电缆最优布置方式。结果显示电缆群布置方式优化能显著提高电缆群载流能力,降低运行温度,对电缆的长期安全经济运行有重要意义。     

Underground cable magnetic field simulation and management using new design configurations

This paper addresses one of the most important sources of magnetic fields: underground power cables. New design configurations for one, two, three and four cables per phase are presented from a magnetic field perspective. Different management techniques are studied in detail. Judicious placement of cable phases in multiconductor lines to reduce the field effect is implemented by computer modeling and simulations. The state-of-the-art magnetic field simulation package PCFIELD developed by EPRI is used to quantify and present the tool used to manage the field values. The new design configuration cases are very useful from a magnetic field point of view and have low cost schemes that can be easily implemented.     

窄通道下排管敷设电缆群负荷优化

电力管道施工过程中,有时不可避免地要经过道路狭窄或地下管网密集的区域,为了保证安全水平净距,通常将此段电缆群变更为通道较窄的布置方式,但这会导致电缆群载流能力减小。将传热学原理和矩阵论相结合,基于IEC 60287提出了一种窄通道下电缆群不等负荷的矩阵优化方案,针对几种典型排管敷设的窄线路建立了有限元模型并进行温度场仿真,验证了优化方案的准确性;最后通过对实际工程通道变窄前后的负荷进行对比设计了合适的窄线路,结果表明该通流方案可提高电缆的利用率,减小了通道变窄对载流能力的影响,窄线路采用不等负荷通流方案可提高电缆的输电能力,随着回路数的增加最大可提升6.53%。     

隧道敷设交流电缆线路的工频磁场特性

城市地下电缆线路对环境及民众的电磁影响在近年引起广泛关注。利用二维有限元磁场分析方法,对典型电缆隧道建模,计算隧道内、外部环境中的工频磁场,研究其空间分布规律,并讨论相关因素的影响。研究发现,随着电缆回路数的增加、敷设密集程度加剧、负载电流增大,隧道内外部的工频磁场增加;与电缆线路之间的距离是决定工频磁场大小的关键要素;磁性支架中容易积聚较大的磁场,降低电缆的经济性及安全性。对几个实际电缆隧道中的工频磁场进行了现场测量,所得数据与仿真计算值吻合较好。计算和测量所涉及的电缆隧道在人行步道及地表所产生的工频磁场强度水平均在标准规定的曝露安全限值以内。     

联合循环M701F单轴机组主厂房布置优化方向

对运用优化辅机设备布置采缩短综合管线的长度,适度压缩主厂房直通道来缩短主厂房跨度和机组中心距的可能性进行探讨．推荐了主厂房布置的优化方向,以达到节约投资,降低运行成本的优化设计方向和思路。     

高压交流电缆线路对邻近金属管道的磁感应影响评估

利用二维有限元磁场分析方法,计算了邻近高压交流电缆线路敷设的金属管道上的磁感应纵电压,讨论并比较了感应电压的不同影响因素。研究发现,电缆隧道壁的钢筋结构可以有效屏蔽电缆线路对金属管道的磁感应影响,管道相对电缆线路的距离和管道材料的磁性是影响感应电压的关键因素,同时,管道尺寸对感应电压也有一定影响。磁感应电压和管道材料的电阻率无关。另外,在电缆线路和金属管道之间采取恰当的屏蔽措施可以有效降低工频磁场对管道的磁感应影响。     

高压单芯电缆单相接地故障护套过电压特性仿真分析

高压单芯电力电缆在敷设过程中,为了限制感应电压、增加单段电缆长度、减少中间接头数量,金属护套层往往采用交叉互联接地.若电力电缆发生单相接地故障,在交叉互联点会感应出较高的过电压,影响电缆使用寿命.对此利用电磁暂态软件EMTP,研究了在单相接地故障情况下高压单芯电缆金属护套过电压特性,分析了电缆整体排列方式、接地电阻、负荷性质、交叉互联各小段电缆长度以及混合排列方式对金属护套过电压的影响程度.研究结果表明:电缆整体排列方式、交叉互联各小段电缆长度和混合排列方式对金属护套过电压的影响较大;接地电阻和负荷性质对感应过电压的影响较小.     

海缆埋设深度检测技术的研究

海底电缆和光缆(简称海缆)的埋设深度检测是海缆施工维护的关键技术之一,文中对海缆周围的交流磁场进行分析推导,介绍了交流磁场探测法的基本原理。提出了一种利用双三维阵列探头测定海缆位置和埋设深度的方法,并进行了较为详细的分析和讨论。     

Interference of nonlinear ferromagnetic pipeline on magnetic fieldproduced by power lines

The investigation of the magnetic field produced by power lines has drawn a lot of attention from researchers. Since sharing space by buried power lines and pipelines has become commonplace, it is of interest to investigate the influence of the pipeline. In this paper, we study the change of the magnetic field produced by buried cables, due to an additional steel pipe nearby. A Fourier series technique is used to calculate the magnetic field. An iterative procedure is employed to handle the nonlinear characteristics of the steel pipe and to determine the varying permeability in it. The calculated results of the magnetic field are compared with those produced by buried cables without the additional pipe. The comparison shows that the steel pipe close to buried cables may significantly alter the magnetic field     

Ampacity of cables in single covered trays

A mathematical thermal model is developed to predict the operating temperatures of cables in a single covered tray when there is load diversity in the power cable bundle. The model accommodates two different loading scenarios: one in which the heat is distributed evenly across the cable tray cross section; and one which concentrates the heavily loaded cables along the centerline, while surrounding them with more lightly loaded cables. The temperature predictions provided by the model are compared to data found in other IEEE papers, data collected in laboratory measurements, and new data from a four-year study of cable trays in an operating nuclear plant. Reasons for differences between the field data and the computer results are discussed. The model is used to evaluate the conservatism in the available Codes and Standards. A derating factor is introduced that is defined in terms of the ampacity of power cables in open-top trays. The derating factor accounts for the added thermal resistance present when a cover is placed over the cables, trapping a layer of stagnant air on top of the cable mass. The computer model is then used to predict values for the derating factor as a function of cable depth. The derating factor is shown to be independent of the composition of cables in the tray. The presence of a cover is shown to reduce the ampacity based on an uncovered tray by up to 25 percent depending on the depth of the cables in the tray     

ADSS光缆在电力通信网中的应用

全介质自承式(ADSS)光缆的设计施工是一项综合性的系统工程。给出了ADSS光缆挂点的空间电位的控制值,在最大弧垂下光缆必须保持与各种交越物的安全距离,ADSS光缆配盘原则及配盘长度经验公式,介绍了耐张线夹、垂悬线夹、防振装置的配置情况,总结了ADSS光缆施工要点。     

沿钢板表面敷设电缆电动力的计算

研究了沿钢板表面敷设的电力电缆的电动力的计算问题。通过详细分析钢板对电缆周围空间磁场的作用,阐明了计算在这种情况下敷设的电缆电动力的一般方法。获得了无限长、圆形横截面的电缆的电动力的单重级数式解析解。讨论了电缆距离钢板的高度等参数对电动力的影响。利用该解析计算公式,计算了一直流供电系统中当某处发生短路故障时的每根电缆的电动力,为电缆束的固定提供了理论依据。并且从更易于电缆束固定的角度出发,对原来的电缆布置方案作了适当的调整,为优化电缆的敷设方案提供了参考依据。     

Prediction of magnetic fields in multiconductor systems withsignificant harmonic currents

Electric and magnetic fields produced by transmission systems have received strong interest both for biological effects and for interference with electrical and electronic devices, measuring sets, computers, control systems, etc. A deeper attention has been more recently devoted to magnetic fields which are difficult to screen and which can be significant when produced by transmission, but also by distribution and utilization systems. This paper proposes a simplified approach which seems to be useful in the case of lines set up by cables and, in particular, when more cables are connected in parallel, considering currents affected by significant harmonics content. Complete simulation results for several selected cases to analyze the electromagnetic field under quasi-stationary conditions in a multiconductor system are reported and discussed in detail, and the main results are summarized. It was found that the parallel connection of conductors can amplify or reduce magnetic field amplitude with respect to the single conductor case and that this effect depends on the harmonics order     

Modeling the effects of distance in single-conductor power cables in a three-phase power system

Single-conductor power cables are widely used in cable lines in Armenia and provide greater current conduction and reliability than triple-conductor cables. In this paper, the optimal distance between single-conductor power cables in a three-phase power system for a given arrangement (horizontal in the plane or triangular) and ambient (ground) temperature are determined. The results for single-conductor cable arrangements are presented in graphical form.     

单芯高压电力电缆金属护套感应电流的研究之一——感应电流的计算和预控

对单芯电缆交叉互联金属护套感应电流进行了研究。为了控制实际电缆线路工程中单芯电缆的护套感应电流,建立了复杂通道条件下,计算单芯电缆护套感应电流的数学模型,提出了通过调整电缆排列来预控感应电流的方法,并编制了相应程序,以实现护套感应电流的计算和预控。全文共分两大部分:第一部分为感应电流的计算和预控;第二部分为计算程序编制和应用。     

单芯高压电力电缆金属护套感应电流的研究之二——计算程序的编制和应用

对单芯电缆交叉互联金属护套感应电流进行了研究。为了控制实际电缆线路工程中单芯电缆的护套感应电流,建立了复杂通道条件下,单芯电缆护套感应电流计算的数学模型,提出了通过调整电缆排列来预控感应电流的方法,并编制了相应程序,以实现护套感应电流的计算和预控。全文共分两大部分:第一部分为感应电流的计算和预控;第二部分为计算程序编制和应用。     

Magnetic field management techniques in transmission underground cables

Magnetic field management is concerned with the minimization of the effects of such fields on the public health, without sacrificing the effectiveness or reliability of the power system. The essential management techniques used for the underground transmission cables comprise geometry manipulation phase placement, and source shielding. In this paper, the simulation results of the standard recommended stack, triangular and flat configurations are presented. The simulations have been carried out for single and three phase cables. The resulting fields for different depths have been evaluated and compared. The results led to the conclusion that judicious placement of phases is a very powerful management technique to reduce the magnetic field as cost has not been changed. The appropriate phase placements corresponding to minimal field values are obtained.