高压直流输电线路离子流场的求解是其电磁环境分析和评估的基础.本文对高压直流输电线路离子流场计算研究现状进行了综述,对其中存在的困难进行了分析,并介绍了相关的研究进展.对目前高压直流输电线路离子流场的研究进行了全景式的描述,对这方面的研究工作具有一定的助推作用.

直流输电线路电晕产生的空间电荷在直流电场力的作用下形成离子流,会显著增强地面电场强度.结合通量线法和有限元法各自的特点,提出一种混合方法求解离子流场,在分裂导线周围的区域采用通量线法,在远离导线的区域采用有限元法,各区域之间采用D-N交替法进行耦合计算.一方面,仅在导线周围采用通量线法,避免了通量线法在全空间由于Deutsch假设产生的误差,并且可以考虑风速影响;另一方面,分裂导线周围不需要网格剖分,能够有效减少有限元网格节点数量,提高有限元计算效率.同时通量线法能够为有限元法提供交界面的初始值,耦合迭代在较少步数内即可收敛.计算结果与实验结果吻合较好,求解效率得到提高.最后,采用该方法对±800 kV与±500 kV直流同塔双回线路地面电场强度与离子流密度进行了预测分析.

通量线法是求解直流线路离子流问题广泛应用的一种方法,其计算误差主要来自Deutsch假设.该文基于通量线(或称特征线)基本理论,提出一种高精度迭代特征线法.通过迭代计算,在每一步采用新的电场分布重新绘制特征线,逐步修正特征线的方向,从而使特征线法不再依赖于 Deutsch 假设.结果表明,与传统通量线法相比,迭代特征线方法在求解地面电场与离子、空间离子流分布、通量守恒性及电晕损耗方面均有明显改善.另外,还对两种传统通量线法边界条件的施加方式进行了误差比较与讨论.

在有风条件下,特高压直流与交流并行线路的空间离子流场除受直流电场与交流电场的共同影响以外,还会在横向风力作用下进行新的迁移运动,进而改变地面混合电场的分布特性.采用区域分解法求解横向风存在时的混合场问题,对方法的边界条件和计算流程均进行了改进.结果表明,处于直流线路下风区的直流电场分量横向衰减速率随着风速的增加明显变缓,而上风区的直流电场大幅减小.因此,风速对于混合电场分布的影响程度与交直流线路的相对位置有关.对于同走廊线路,当交流线路处于直流线路下风区时,横向风明显增强了交流线路附近区域内直流分量;而当交流线路处于上风区时,即使风速很小,交直流线路之间的走廊内直流分量也会基本衰减至标称电场.对于同塔线路,由于交直流电场各自的部分特点,横向风不会增强交直流分量的叠加效果.

The ion-flow environment is an important corona design factor of HVDC transmission lines. The space charges generated by corona form a typical convection-dominated ion-flow field. For this special transport phenomenon, however, standard Galerkin FEM always presents serious deficiencies. In this study, a new approach is used to solve ion-flow field based on Petrov-Galerkin method derived from the theory of fluid computation. A high-order stabilisation technique is used to overcome the non-physical oscillations in the presence of highly convective effects. This algorithm is equivalent to the proper modification of weight function according to the direction and magnitude of local drift velocity. It reflects the characteristic of information propagation in flow problem. The establishment procedure of weak form and matrix gives a further explanation on the deficiency of Galerkin method. Moreover, to guarantee convergence of the iteration for this fully-coupled non-linear problem, a relaxation method is introduced in the iterative loop. Calculations with the Petrov-Galerkin least square method are in good agreement with analytical solution and experiment values of ground-level values and corona losses. Results show that the proposed stabilisation technique is able to preclude the numerical spurious oscillation and has a higher-order accuracy than the fully-upwind treatment.

1 前言 随着国家“西部开发”、“西电东送”战略的实施,河西走廊通道内密集分布着电力线路、铁路、高速公路、油气管线等各种设施,廊道拥挤,已建的哈密-郑州±800kV直流线路、正在建设的准东-华东送出±1100kV、规划建设准东-成都±1 100kV直流输电线路工程及多条750kV、330kV也将从此通过,因此有利用已有的330kV通道,采用1100kV与330kV同塔多回输电技术是解决河西走廊电力通道问题的有效手段.

Hybrid electric field of ac/dc transmission lines on the same tower is a most important factor for line configuration design. Lateral profile of electric field on ground has close relationship with superposition and distribution of ac and dc component. In this paper, hybrid electric field and ion current are calculated and analyzed for double-circuit 330kV or 750kV ac lines and?1100kV dc lines on the same tower with different configuration and phase sequences. Minimum conductor heights and corridor widths are also computed. Results show that electric field profile on ground level can be categorized into three regions: ac, hybrid and dc. ‘Inverted triangle’ and ‘vertical’ structures are proposed to be used to separate positions of peak values of dc and ac components. Corridor widths are determined by ac field for 750kV lines while by both ac and dc fields for 330kV ac lines. Finally, configurations I (phase sequences 6) and II (phase sequences 4) are proposed for hybrid ac/dc lines on the same tower.

It is an effective way to restrict electric field and ion current on ground level by installing shield wires. Due to space charge, electric field strength on shield wire surface is significantly increased. Therefore, whether corona occurs on the shield wires depends on total electric field rather than space-charge-free field. In this paper, domain decomposition method is used to analyze shielding effect of shield wires. Corona from shield wires is taken into consideration in iteration loop. Different methods are used to predict ground-level electric field and ion current density of a reduced scale model. Calculations are compared with measurements and reasons causing error are analyzed. Results indicate that earth corona will enhance shielding effects because space charges generated from shield wires will recombine with ion current from dc conductors. Earth corona should be taken into consideration in numerical method. Finally, electric field of a typical ±800 kV HVDC transmission line is analyzed and shield wire arrangement is discussed.

Building HVdc and HVac transmission lines in the same corridor or even on the same tower is an attractive way to extend electricity transport capacity where getting the new right of way is difficult. The resulting hybrid lines produce a new corona performance, such as ground-level hybrid electric field and ion current density, which are quite different from those of pure ac or dc lines. In this paper, inherent space-time pattern and characteristics of the information propagation in Lagrangian description are presented for the ion transport problem, that is, the ion density at a certain point has a direct relationship with its drift time. Based on this, the theoretical explanation is provided for the decoupling algorithm, by which the ground-level dc component can be solved with the ac conductors assumed to be at zero potential and vice versa. The simulation results show that the sinusoidal ac field has negligible influence on the dc ion drift time from conductor surface to ground, whereas stationary electric field generated by the grounded ac lines has a dominant effect. Therefore, ac energization has a rather low impact on ground-level quantities and the simplification of grounded ac conductors is quite reasonable.

It is an attractive way to build the ac/dc hybrid overhead lines to increase the capability of scarce transmission corridors. In this paper, a new approach is present to solve the fully coupled ion-flow problem of ac/dc hybrid lines. The 2-D transport equation of ions is transferred to 1-D fully coupled characteristic equations along each flux line, based on the methodology of the flux tracing method (FTM). An iterative process is proposed to reduce the error due to Deutsch assumption used in FTM. The calculation is efficient as only 1-D transport equations are solved. The iteration converges within only a few times since all the boundary conditions can be satisfied at each step. Results coincide well with measurements and calculations in the previous literature. Comparison shows that Deutsch assumption may lead to significant errors for the hybrid models and the proposed modification should be used.

It is an efficient technology to build HVAC and HVDC transmission lines on the same tower in area with insufficient right of way, where electromagnetic environment is an important issue. In this paper, domain decomposition method based onstationarysimplification is applied to compute electric field and ion current density on ground level. The second-orderelements are used in ambient space of conductors while the first-order ones are applied in space far away from the conductors. D-N algorithm is used tocompute coupling in each domain. A new iteration scheme is proposed based on corona discharge U-I curve. Ion density is updated with calculated voltageratherthanelectric field strength. Thus error caused by interpolation in one element is reduced. Results obtained with this method are compared with previous data, showing that the proposed domaindecompositionmethod based on simplification of zero ac voltage can be used to predict electricfield ofhybrid lines withcomputation efficiency improved significantly.

The electric field and ion flow are significantly influenced by the transverse wind around the high-voltage direct current (HVDC) transmission lines. In this study, a new method using local characteristics is proposed to analyse the effect of wind. The present method, called method of local characteristic, updates the ion density based on the local characteristic curve in each second-order finite element method (FEM) element without Deutsch assumption. The defining equation of the characteristics is able to take into account the directional character of the information propagation in convective transport and has a better performance to satisfy the conservation law. The present approach is stable and efficient even in the presence of high-speed transverse wind. Calculations show good agreement with the measurement values of the reduced-scale unipolar model and the full-scale bipolar test line. Finally, the influence of wind on the electric field and ion current is discussed.

A combined method adopting the domain decomposition is proposed for analyzing the ion-flow field of high-voltage direct current transmission lines, including the effect of the transverse wind. The upstream finite-element method is used with a dense triangle mesh in the vicinity of bundle conductors to guarantee the accuracy. The upstream finite-difference method is proposed and the larger uniform quadrilateral grid is applied to simulate the ion-flow field in the rest of the region with a satisfactory precision. The calculation process of the Poisson equation is iterated with the Dirichlet-Neumann algorithm to coordinate the solution between adjacent subdomains. The proposed approach improves the efficiency and remains stable with high wind speed. Finally, the influence of wind on the ion-flow field is analyzed and calculations are in good agreement with experimental data and results in the previous literature.

The electric field and ion current distribution on the ground level and corona losses are the important factors for designing high-voltage direct current (HVDC) transmission lines. This study presents a new finite-difference-based flux tracing (FDFT) method for analysing the ionised field. The differential equations are discretised using the finite-difference method and the non-linear algebraic equations are constructed. For the bipolar field, a systematic technique to set up the initial values is well established by estimating the average values of space charge density. The issues of the finite-difference scheme, the normalisation and the selection of mesh points are elaborately discussed to have a better convergence. The boundary conditions of the ionised field equations can be enforced directly, whose benefit is that the iterative process to satisfy the boundary conditions can be completely avoided. The numerical examples show that the results obtained in this study agree well with the ones published in other literatures. The FDFT could be applied for more complicated line configuration with unequal corona-onset electric fields and ion mobilities of opposite polarities.

This paper focuses on the calculation of the ion flow field and total electric field of high voltage direct current(HVDC) transmission lines. Based on the method for calculating ion concentration in the coordinate system of the flux lines, differential equations and boundary conditions are obtained. A new method is presented, which transforms these differential equations to nonlinear algebraic equations by finite difference method. This method reduces the computational difficulty of differential equations and improves the calculation speed. In addition, it can be applied to solve both unipolar and bipolar ionic charge flow.