保角变换在计算绝缘偏心对射频同轴电缆电性能影响中的应用

本文论述了保角变换法计算绝缘偏心对射频同轴电缆电性能影响的方法,并给出了相应的电容、电感、特性阻抗及绝缘电阻的解析函数表达式,最后与数值计算结果进行了对比。     

Algorithm to predict dry-band arcing in fiber-optic cables

Utilities frequently use ADSS (all dielectric self-supporting) fiber-optic cables installed on transmission lines 3-6 m below the high voltage conductors. Dry-band arcing occurs on the fiber-optic cables when the cables are polluted and wet. This has been assumed to cause cable failures. An equivalent circuit has been developed to represent the polluted fiber-optic cable in the high voltage environment. The objective of this paper is to present a novel numerical method that can be used to predict dry-band arcing in fiber-optic cables. KCL (Kirchoff's current law) is used to derive node point equations for the equivalent circuit. Forward elimination and backward substitution of node voltage is used to solve the equations. The effect of pollution, tower arrangement, and conductor sag is analyzed. The numerical method has speed advantages over circuit simulation methods. This method includes conductor sag, nonuniform pollution, and variable capacitance. This algorithm can be used to predict dry band arcing in fiber-optic cables     

A model to predict current distributions in bundled cables forelectric glass melters

A model for predicting the current distribution in high-current cables that are constructed from bundles of parallel conductors (strands) is presented. These cables are typically used in electric glass melters to interconnect the power transformers and the melter secondary bus installations. Due to the phenomenon known as the skin effect, the magnetic field forces inside the bundled cable will tend to drive the current toward the outermost strands. The proposed model is developed by starting from the fundamentals of the skin effect phenomenon for solid conductors and then extending the concept for bundled cables. The model has also been coded in a simple FORTRAN computer program. Results obtained using the proposed model for a variety of cable bundling configurations are presented for demonstration purposes. These results show that currents in the outermost layers of bundled cables can exceed those of the innermost layers by a factor of four or more, depending on the total cable size     

Current rating of multicore cables

An algorithm to calculate the current-carrying capability of multicore cables is presented. The method takes into account the presence of air gaps and metallic conductors in the cable bundle. Under an assumption of a uniform loss density, analytical expressions, which take into account conduction inside the bundle and convection and radiation outside it, are developed. The method is illustrated with a numerical example of a telecommunication cable with 96 stranded cores. Experimental results are also reported for the same cable.     

EMP作用下的电缆耦合及屏蔽效能试验分析

介绍了三同轴法、线注入法、功率吸收钳法、混波室法等电缆屏蔽效能测试方法.进行了电磁脉冲作用下的同轴电缆和裸线耦合试验,探讨了该环境下同轴电缆屏蔽效能的测试方法.试验分析表明,电缆耦合后的波形为衰减振荡波,振荡周期正比于电缆的电长度,频谱与照射场的频谱不一致,裸线的耦合输出衰减较快.根据试验数据,采用峰值场强法计算的电缆屏蔽效能与峰值电压法的结果吻合,所以可采用峰值场强法对电缆进行电磁脉冲的屏蔽效能测试.电磁脉冲作用下的同轴电缆屏蔽效能较相当频段连续波作用下的略低.     

Numerical calculation of AC substation grounding systems buried in a vertical multilayered earth model by higher‐order basis function

To study the accuracy of numerical simulations for an AC substation grounding problem embedded in a vertical multilayered earth model, this paper proposes a novel algorithm combining the rapidly convergent one‐dimensional Galerkin's BEM with higher‐order basis functions on the basis of the quasi‐static electric field theory. General analytical formulas for the mutual impedance between any pair of short line conductors are also derived to accelerate the numerical integration. These formulas can work in not only complex space but also real space because of our application of the quasi‐static complex image method, which is different from the contribution of other earlier scientists, whose formula can work just in real space. The algorithm can be used to simulate and analyze any grounding system, including those incorporating a floating grid located anywhere in the earth model. Copyright © 2011 John Wiley & Sons, Ltd.     

等传输容量铜、铝导体海缆技术经济性比较

针对铜资源日益紧张造成电线电缆行业原材料成本压力的问题,分析铜、铝材料性能差异,完成等传输容量下铜、铝导体截面换算,依据现有生产工艺,采用解析法,完成铜、铝导体海缆参数计算,对比分析铜、铝导体海缆的技术经济性,进一步研究铝导体连接性能。结果表明：等传输容量条件下,铜、铝导体海缆单位质量近似相等,两者损耗及短路电流特性相近,铜导体海缆材料成本为铝导体海缆的110%~180%,采用交流氩弧焊可使铝导体接头具备良好电气与机械性能,铝导体海缆经济性更优。     

电气化隧道中的导线-地回路阻抗

在电力系统，特别是在电气化铁道中，会遇到导线架设在隧道中的情况，过去一直采用Carson公式计算隧道中导线的阻抗，但采用Carson公式计算隧道中导线-地回路阻抗存在固有模型误差。在比较半无限平面大地模型和四周无限大地圆形隧道模型基础上，提出电气上的长大隧道概念。结合电气化铁道隧道实例，进行对比计算，给出Carson公式所导致的误差。结果表明阻抗误差随频率的增高而增大，随大地电阻率的增大而减小，即使在工频下仍超过5%。进而从物理概念上分析两种模型的差别，讨论在长大隧道中采用Tylavsky公式的合理性。     

通信电缆绝缘单线加工工艺参数的计算

介绍长途对称通信电缆中绝缘单线加工工艺参数的计算。根据长途对称通信电缆工作电容标准值 ,可分别计算出绝缘单线的外径和同轴电容 ,并可计算出挤出机出胶量 ,以及氮气的注入量。另外 ,对挤出温度设置和模具设计等也进行了讨论     

Skin effect in a bifilar lead consisting of cylindrical conductors

The electromagnetic field of a bifilar lead consisting of two thick cylindrical conductors carrying an alternating current is investigated by using the Bubnov-Galerkin method. The electrodynamic forces acting on these conductors and their inner impedances are examined. By digital computations the graphs of the forces and impedances are given for conductors with equal radii.     

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.     

Ampacity of wrapped cables

Analytical equations that permit quick computation of the ampacity of power cables wrapped with refractory silica are presented. Ampacity test results are given for several wrapping methods and cable configurations. These test results show that the analytical method is reasonably accurate in determining the ampacity of wrapped cable     

Skin and proximity effects in nonmagnetic conductors

The skin and proximity effects in cylindrical and nonmagnetic conductors are considered. The cross sections of these conductors can have arbitrary shape. A procedure is presented for computation of current densities over the sections and an expression for the calculation of the impedances matrix is also developed. The equations are written in a generalized form, which is useful in studying systems of several parallel interacting conductors. Using mathematical software, these two effects can be simulated and the behavior of impedances, losses, and coupling when electrical parameters and geometrical configuration are modified can be analyzed.     

Sizing of cables in randomly-filled trays with consideration forload diversity

A method for demonstrating increased ampacity of cables in trays with loading diversity is given. Ampacity tables for sizing cables in randomly-filled cable trays are provided in NEMA WC 51-1986 based on a model developed by J. Stolpe which ensures that the maximum cable temperature does not exceed the insulation rating (typically 90°C) under worst-case conditions. The Stolpe model intentionally disregards the reduced heating effect of deenergized or lightly-loaded cables to ensure that all possible hot spot conditions are enveloped. Other methods have been proposed to credit loading diversity in order to justify increased ampacity. However, since they involve certain assumptions about the heat distribution within the cable mass, these methods may fail to identify individual overloaded conductors. This paper describes a simple method which considers the performance of individual conductors while providing a means of increasing ampacity as a result of loading diversity     

Wave propagation on power cables with special regard to metallic screen design

The high frequency properties of coaxial power cables are modeled using time- and frequency-domain numerical simulations. This is required due to the complex helical structure of the outer metallic screen. The finite element (FEM) and finite difference time domain methods (FDTD) have been employed to study the effect of screen spiralization. It is established that this screen design causes a dependence of the cable high frequency characteristics on the surrounding medium. Analytical model based on modal analysis of wave propagation in coaxial cables confirms the numerical observations     

A one-step finite element formulation for the modeling of singleand double-circuit transmission lines

A method is presented, by which a finite element method (FEM) formulation is used for the direct computation of overhead transmission line series and sequence impedances. The method is applied in single and double circuit line configurations of arbitrary geometry, giving results in perfect agreement with those available from classical calculation methods. The new method can easily handle cases of nonhomogenous and/or irregular terrain, where classical methods may fail     

电极表面场强数值计算方法的比较

介绍了电极表面场强计算的曲率半径法、多点逼近法和综合法,给出了相应的计算公式和误差估计公式.并用球电极和同轴圆柱电极比较了三种数值方法的场强计算误差.结果表明,综合法效果较好.     

Dependence of XLPE insulated power cable wave propagation characteristics on design parameters

Propagation losses occur in medium voltage power cables as pulses propagate through them. Since cables have many components, these can make different contributions to the propagation losses. The relative contributions of the conductors, insulation and semi-conducting screens to the propagation characteristics of the cable are analyzed. The propagation characteristics of the cables are studied by a developed "approximate" model providing analytical expressions that can quantify the contributions to the losses by the different parts of the conductor and dielectric system. The model is compared with an "exact" model and is tested on four cables     

Calculation of horizontal displacement of conductors under windloading toward buildings and other supporting structures

Wind loadings can be the determining factor in the structural design and location of supporting structures, including the choice of materials, sizes, and configuration. Deflection of structures or supported facilities under wind loading may require increased clearances between conductors or cables, thus affecting the physical design of the structures, as well as requiring increased clearances from buildings and affecting the location of the structures themselves. Both exact methodologies and rules of thumb are presented for calculating horizontal loadings and wind deflections of conductors and cables. Tables give values for common conductors that may be used in determining compliance with the National Electrical Safety Code     

混合电磁结构磁性部分元等效电路建模技术的解析及实验研究

磁性材料在电磁结构中广泛应用,而传统(标准) 部分元等效电路(partial element equivalent circuit,PEEC)方法对包含磁性材料的各种结构进行分析时已无能为力。针对基于几何平均距离和空间磁介质均匀化处理的新型磁性PEEC建模方法(magnetic PEEC,MagPEEC),该文提出使用同轴电缆解析计算以及大型钢板耦合与邻近效应实验对该建模方法进行验证。利用解析法对给定同轴电缆单位长度电阻与电感参数进行了计算,并将计算结果与由MagPEEC建模计算的结果进行了比较;分大型舰船钢板差模回路耦合和共模回路耦合干扰两种情况,对MagPEEC建模计算的耦合阻抗进行了实验验证;利用所研制的钢板地电流测量装置在钢板中部进行测量,并将测量结果和MagPEEC理论计算的结果进行比较,从而实现金属壳体地电流测量和MagPEEC理论计算方法的直接验证。利用该文所提供的解析方法和3种实验方法,对MagPEEC建模技术进行了充分证明,为MagPEEC建模技术的推广使用奠定了基础。