Calculation And Analysis Of Ion Flow Field At The Crossing Of HVAC/HVCD Transmission Lines

Increasing HVDC(High Voltage Direct Current)transmission projects make new HVDC lines cross over the original HVAC(High Voltage Direct Current)or HVDC lines frequently.To ensure the safety of nearby staff and control the influence on surrounding environment,it is necessary to conduct reasonable calculation and analysis for ion flow field at the cross of HVDC and HVAC transmission lines.In order to study the electric field environment at the crossing of HVDC lines,after the comparison of simulation result between COMSOL Multiphysics(FEM)and FLUENT ANSYS(FVM),a 3D simulation method for ion flow field that is based on FLUENT secondary development is proposed in this paper,which avoids the huge work of constructing a 3D partial differential solver by all the self-written programs.In this method,C language program is used to define the scalar transport equation and boundary conditions,bundled conductors are equivalent to single conductor,the first order upwind difference scheme for ion transport equation is applied at the boundary to ensure convergence,surface charge density distribution that satisfies Kaptzov hypothesis is obtained by cyclic calculation and iterative modification and all calculation is conducted on fully-structured grid.Moreover,the nominal potential at the artificial boundary is given by the same solver and the additional CSM(Charge Simulation Method)is not needed anymore.The validity of this proposed method has been verified by analytical solution of coaxial cylinder and measured value under actual HVDC lines.In this paper,the situations that HVDC lines cross HVAC lines in different ways are simulated,then the influence of HVAC lines on the ion flow field of HVDC lines and the distribution laws of ion flow at ground level under different crossing angles and vertical distances are analyzed.In the calculation of hybrid electric field,the power frequency voltage of HVAC lines is replaced by the average voltage,the stop condition of surface charge density correction is set as:the average field strength of the whole wire surface is equal to the onset field strength,instead of achieving equality everywhere.At the same time,a more scientific surface charge density correction formula is used to get the value of surface charge in the next round of calculation.Finally,this paper extends the simulation method above into the calculation of ion flow field in the crossing area between two circuits of HVDC lines.Based on the calculation results,the interaction rules of the HVDC lines and the complex changes of ground ion flow field distribution in different crossing angles and vertical distances are analyzed.All the above methods have been verified by the published experimental data and proved to be applicable to the prediction of ion flow field in actual high-voltage line crossing situations.