不同气象条件下特高压输电线路工频电场计算与档距选择

气象参数变化引起输电线路荷载、应力和弧垂变化,进而影响线下工频电场,该问题对特高压线路尤为突出。为此,讨论了架空悬链线方程及弧垂影响参数,建立了输电线下工频电场三维计算模型,采用改进的模拟电荷法推导出包含气象参数和档距的电场计算式。以紧凑型特高压输电线路为例,研究地面电场分布特性,重点比较不同气象条件下不同档距线路最大弧垂和距地1.5m处的最大电场强度。结果表明,三维模型能够定量计算不同气象条件和不同档距时特高压输电线下电场;在诸多影响因素中,温度和档距尤为突出。     

HVDC输电线路离子流场数值计算方法研究

为了解高压直流输电线路的电磁环境影响及电晕损耗,讨论了高压直流线路周围离子流场计算的数值方法。描述高压直流离子流场控制方程的三阶非线性偏微分方程分解为两个等效的泊松方程后可用有限元迭代方法求解即在每次求解后根据两场的计算结果更新空间电荷密度,反复迭代求解直至计算结果收敛。该算法舍弃了Kaptzov和Deutsch假设,并提出了一种有效的电荷密度更新公式,同时考虑两场电位差别、电场与边界条件的差别,使迭代较快收敛。通过与实验模型的测试结果对比,验证了算法的有效性。     

40.5 kV SF6充气式开关柜三维电场分析

建立了40.5 kV、2 000 ASF6充气式开关柜的三维电场分析的有限元模型。针对产品实际结构的复杂性,应用网格划分控制工具的参数设置和疏密网格等分网方式对模型进行网格划分,按照实体模型的边界线或边界面的曲率排布设置了中间节点、边中节点,使有限元模型与实体模型的边界更吻合。同时采用局部细化、重新分网等方法提高网格的质量。考虑大型稀疏方程组迭代收敛以及收敛速度快慢的问题,通过几种求解方法的比较,选用不完全乔类斯基共轭梯度(incomplete Cholesky-conjugate gradient,ICCG)算法进行大型有限元方程组的求解。该文通过计算分析获得了充气柜2个气室(隔离开关室和断路器室)的电位和电场强度的分布规律,以及相关结构参数对电场分布的影响,从而对SF6充气柜(cubicle gas-insulated metal-enclosed switchgear,C-GIS)的绝缘结构设计提供理论参考。     

特、超高压交、直流并行输电线路周围混合电场的测量方法

由于交、直流并行输电线路周围电场既有直流分量,又有交流分量,为混合电场,传统的仪器无法直接开展测量工作。为此,在分析现有直流线路地面电场测量装置(旋转伏特计)、地面离子流密度测量装置(离子流板)测量原理的基础上,研究了交、直流混合电场下已有测量设备输出结果的频谱特征,建立了交流和直流电场与测量结果频谱的对应关系,从而提出了交直流并行输电线路下同时考虑直流和交流分量的地面电场和离子流密度测量方法。在缩尺模型下的实际测量和分析表明,所提出的交、直流混合电场下地面电场和离子流密度的直流和交流分量测量方法是有效的。     

多路供电系统高压输电线考虑弧垂的场强计算模型

交流输电线路附近的空间场强是随时间变化的,在电磁环境保护和ADSS光缆架设中都需要计算出空间点在一个时间周期内的最大场强值,而对于实际输电线路还要充分考虑弧垂的影响。针对上述情况,采用等效电荷法,在考虑弧垂时分别基于频域和时域建立了多路供电系统高压输电线下的分段三维计算模型,并推导出了相应的最大场强计算公式。比较两种模型发现时域模型占用内存较少且延拓性较强,建议采用时域模型。最后用其公式编程对一条输电线路进行了计算比较,得出所推导的最大场强公式计算结果比以往场强计算结果更准确,弧垂对输电线路的最大场强有很大的影响,输电线路的场强计算应该采用三维模型。     

Transmission line modeling with explicit grounding representation

This paper presents a new model of an overhead transmission line for electromagnetic transient computations. The unique feature of the model is the explicit representation of the tower grounding configuration and terminal substation grounds. Other properties of the model are: (1) accurate frequency dependent parameter representation from DC to several MHz; (2) explicit modeling of line asymmetries; and (3) high numerical efficiency.The model implementation is based on the solution of the transmission line differential equations resulting in a set of step response functions, forming a matrix. The step response matrix is utilized in a time domain simulation of electric power networks by a linear convolution scheme. The transmission line model is validated with actual system test data. The model is useful for computing the ground potential rise of transmission towers due to lightning or switching surges, insulation stress, etc. Typical applications are described in the paper.     

复杂地势下超高压输电线路的工频电场

为精确研究超高压输电线路穿越较复杂地区时的工频电场,基于模拟电荷法引入最优化方法,建立了相应的二维电场计算模型和计算公式。通过设置自动寻求最佳模拟电荷仿真电场分布的结果表明,此法合理可用。     

绞线花纹导线表面电场强度计算与分析

为了准确计算输电绞线花纹多股绞线表面电场强度的大小,建立了二维电场模型,采用有限元法与镜像法相结合的方法计算带有花纹的输电线表面场强,并与光滑导线模型的场强进行比较,还分析了绞线花纹对导线表面最大场强的影响。考虑输电线表面花纹后计算出的表面最大场强与将导线视为光滑圆柱体的计算结果相差>20%。在导线选型时,应充分考虑绞线花纹对导线表面最大场强的影响。     

积分方程法在埋弧炉三维磁场计算中的应用

积分方程法使埋弧炉三维磁场计算成为可能.本文以挪威25MVA埋弧炉为算例,介绍了积分方程法在埋弧炉三维磁场计算中的应用,算例结果与工程运行经验相吻合,并对工程设计起指导和参考作用.     

Field distribution in cable terminations from a quasi-staticapproximation of the Maxwell equations

A new model for the evaluation of the electric field in a cable termination realized through a nonlinear stress control tube (SCT), is presented in this paper. It is based on the electro-quasistatic approximation of the Maxwell equations: the Laplace equation describes the field in the nonconducting regions whereas a diffusion-like equation gives the field dynamics in the stress control tube. A numerical model is devised by solving the Laplace equation by finite difference and diffusion equations by the Galerkin method. It is shown that even the well-known RC transmission line model can be derived from this general approach. The underlying approximations leading to the circuital model are discussed in detail. The proposed model, in contrast with the circuital one, allows us to take into account properly the nonlinear SCT characteristics and the actual boundary conditions: in this way both spatial and temporal effects of the nonlinearity are-considered. The numerical results obtained by considering the general field approach and by using the transmission line model are compared     

Electric field calculation in composite dielectrics by surface charge method based on electric flux continuity condition

We propose a new surface charge method based on the continuity of electric flux passing through each partial area on the dielectric boundary. N partial areas divided on the boundary give the boundary equations for solving N unknown variables representing the surface charge density distribution. The electric flux is numerically calculated by integrating the normal component of electric flux density on each partial area. This method permits us to exclude the singularity of edge parts from the boundary equations because these parts do not contribute to the integration area. In this paper, we apply first‐order functions to simulate both triangular surface shape and charge density distribution on its surface as well. First, we have computed the electric field for a spherical dielectric under a uniform field. The calculated results show that the accuracy of the electric field at the spherical center is almost equal to the accuracy of the total surface area of the polygon which represents the sphere. Furthermore, this method has improved the accuracy of the field by about one order compared with the conventional surface charge methods. Second, we have computed the electric field for a dielectric human model under a uniform field. The calculated results demonstrates that the proposed method works well for a complicated shaped object with a dielectric constant greatly different from that of an ambient medium. © 2002 Scripta Technica, Electr Eng Jpn, 138(4): 10–17, 2002; DOI 10.1002/eej.1133     

Application of artificial neural network methods for the lightning performance evaluation of Hellenic high voltage transmission lines

Feed-forward (FF) artificial neural networks (ANN) and radial basis function (RBF) ANN methods were addressed for evaluating the lightning performance of high voltage transmission lines. Several structures, learning algorithms and transfer functions were tested in order to produce a model with the best generalizing ability. Actual input and output data, collected from operating Hellenic high voltage transmission lines, as well as simulated output data were used in the training, validation and testing process. The aims of the paper are to describe in detail and compare the proposed FF and RBF ANN models, to state their advantages and disadvantages and to present results obtained by their application on operating Hellenic transmission lines of 150 kV and 400 kV. The ANN results are also compared with results obtained using conventional methods and real records of outage rate showing a quite satisfactory agreement. The proposed ANN methods can be used by electric power utilities as useful tools for the design of electric power systems, alternative to the conventional analytical methods.     

大电流互感器内磁屏蔽方案的性能比较

为比较大容量发电机出口处大电流互感器"两对反极性串"与"4段全并"缠绕两种内磁屏蔽方案抵御外磁场干扰的效果,首先通过电路分析比较了上述两种方法下的平衡电流值、平衡绕组损耗,然后对大电流互感器的温升和误差进行了定性比较,最后通过实验进行了验证。研究结果表明,在平衡绕组缠绕方式相同的前提下,采用"两对反极性串"连接方案的大电流互感器的温升低于"4段全并"方案,而其测量误差高于"4段全并"方案。该结果可为1000MW及以上容量发电机组用大电流互感器设计制造方案的确定提供指导性原则。     

一种基于最小二乘支持向量机的年电力需求预测方法

针对电力系统年用电量增长的特点,将最小二乘支持向量机LS-SVM(least squares support vector m a-ch ine)回归模型引入年电力需求预测领域,并给出了相应的过程和算法。与常规基于人工神经网络ANN(ar-tific ial neural networks)的智能预测方法比较,该模型优点是明显的:1)将神经网络迭代学习问题转化为直接求解多元线性方程;2)整个训练过程中有且仅有一个全局极值点,确定了预测的稳定性;3)将年电力需求预测的外插回归问题转换为内插问题,提高了预测精度。应用实例表明:该模型实现容易、预测精度高,更适合年电力需求预测。     

利用电磁暂态分析软件实现Taylor模型的方法研究

常用电磁暂态分析软件,如ATP-EMTP,PSpice等,具有多种电力元件模型,部分还具有传输线的分布参数模型,然而,它们都不能直接研究场-线耦合问题,而场-线耦合传输线模型能完成这项工作,但是无法利用现有电磁暂态软件直接实现它们,Taylor模型是其中常用的一种。为了利用内含分布参数传输线模型的电磁暂态分析软件实现Taylor模型,基于电路理论推导了Taylor模型新型等效电路,使之符合ATP-EMTP等电磁暂态分析软件的分布参数传输线建模特点。分别利用ATP-EMTP软件基于所推导的Taylor模型等效电路,以及Matlab软件基于Fourier变换和逆变换方法,对算例给出的传输线耦合外场的电磁暂态响应进行了计算,结果表明2种方法计算结果较符合,证明所推导的Taylor模型等效电路是正确的,可以利用电磁暂态软件ATP-EMTP对其进行建模。该研究结果的应用可降低场-线耦合研究的复杂度。     

大气压氦气介质阻挡辉光放电的数值仿真计算

通过精心选择一维模拟计算所需要的各个参数,使用有限差分法数值求解了大气压氦气介质阻挡辉光放电数学模型中的离子连续方程、电子连续方程、泊松方程以及相关的辅助方程,得到了与实验吻合度很好的仿真波形。在此基础上计算了电场、离子密度、电子密度等放电空间内部参量随时空的演化图,这些参量对定量分析大气压氦气辉光的放电机理有重要作用。从理论上对所得到的计算结果做出了解释,并使用仿真结果很好地解释了实验所拍摄到的放电图像。     

特高压角钢铁塔无源干扰计算的三维面模型

为更准确地计算特高压输电线路对各类无线台站的无源干扰防护距离,提出建立单基角钢铁塔无源干扰三维面模型的方法。依据输电线路无源干扰的线、面电场积分方程,分析已有铁塔线模型的等效依据和高频段误差增大的原因。为保证铁塔感应电流的连续性,有效体现角钢的局部特征,提出基于三角面元的铁塔有(无)辅材的三维面模型。选择RWG(rao-wilton-gisson)基函数和伽略金检验,采用矩量法计算铁塔面模型无源干扰水平,并与线模型计算结果进行比较。结果表明,随着计算频率的增高,铁塔线模型与面模型的计算结果变化趋势相同,数值差异逐渐增大。如以0.1 dB为偏差允许值,建议在16.7 MHz以上频率采用更能模拟实际情况的特高压铁塔面模型。     

基于改进电气几何模型的绕击跳闸率的计算

讨论了经典的电气几何模型(EGM),在此基础上提出了3点改进建议。计算中采用IEEE推荐的击距公式,引入系数ksg描述雷击地线和雷击地面击穿强度的不同,用暴露距离计算雷电绕击率和绕击跳闸率。分析了ksg取值对计算结果的影响。利用改进的计算方法、分别计算了地面倾角、避雷线保护角和环境温度对线路绕击跳闸率的影响。结果表明,当ksg减小、地面倾角增大、避雷线保护角增大、温度降低时,绕击跳闸率增大。     

有限元法分析高压架空线路附近电场分布

为准确得到实际建筑物及其周围场强分布,应用三维有限元法分析高压架空线路附近建筑物及其邻近区域中的电场分布。采用的模型考虑了高压架空线和实际建筑物(即建筑物墙壁、楼层间钢筋等)结构,并用六面体单元剖分整体模型以减少三维模型单元数量和提高计算精度。再应用子模型法校核计算结果的准确性,然后分别计算空间中有建筑物时房屋顶部和内部和无建筑物时同样位置的电场分布。最后讨论建筑物对其外部电场的畸变作用及对其内部电场的屏蔽作用。结果表明:架空线路附近的建筑物会改变空间电场分布,且建筑物附近电场强度的最大值出现在建筑物外廓尖角处。     

Dispersion relation calculation of photonic crystals using the transmission line matrix method

In this paper we present the use of the transmission line matrix (TLM) method as a modelling tool for the computation of the dispersion relation of photonic crystals (PCs). First, the formulation of a complex‐valued TLM algorithm for the implementation of the periodicity condition on the sidewalls of the simulation domain (unit cell), is presented in detail. Then, the stability issues of this formulation are analysed from energy considerations. The analysis shows that the TLM method remains unconditionally stable since the equations enforcing the periodicity condition allow for the energy to be preserved as a constant during the simulations. Finally, the complex‐valued TLM algorithm is validated by simulating two PCs and by comparing the results with those predicted by alternative methods. Copyright © 2004 John Wiley & Sons, Ltd.