| The development of UHVDC transmission technology is to solve the uneven distribution of energy and electric load in China.Since there are dozens of HVDC transmission lines in operation and planning in China,the crossing issue of two circuit DC transmission lines is inevitable.The corona discharge of the two lines and the interaction between them make the distribution of the total electric field on the ground complicated.In order to improve the electromagnetic environment and the technological level of HVDC projects,it is necessary to study the 3D modeling and calculation methods of ion flow field when the crossing issue of HVDC transmission lines happens.Positive and reasonable technical references are provided for the transmission lines which are under construction and planning.Firstly,3D modeling and calculation method of the total electric field under the crossing of two circuit DC lines are optimized.The shape and size of the artificial boundary are discussed.Appropriate crossing regions and boundary conditions can reduce the calculation time.Based on the Upstream FEM(finite element method),the Poisson equation and the current continuity equations are solved by Galerkin scheme,which improves the calculation accuracy.Then the traditional 3D simulation charge method is optimized.Quadratic charges are applied in CSM(charge simulation method)to assure the calculation accuracy of the space-charge-free electric field.Besides,the optimized algorithm provides a theoretical basis for setting the artificial boundary conditions.Secondly,the smooth conductor and the actual conductor model are selected for the crossing experiment,which is carried out to validate the optimized method.And then the distribution of the total electric field on the ground is analyzed with different voltages under distinct crossing angle and different corona state.Finally,the distribution of the total electric field on the ground is predicted based on actual transmission lines model.Characteristics of space-charge-free electric field and ion flow field on the ground and are calculated when the 1800kV lines cross the ±500kV lines.Then the factors affecting the total electric field on the ground are analyzed.The distribution of the total electric field on the ground is discussed considering the influences of voltage,height,vertical spacing,and cross angle.The research work in this thesis can provide a reference for engineering prediction and environmental assessment of HVDC transmission lines. |
