Calculation Methods For Ion Flow Field From HVDC Transmission Lines Parallel With HVAC Transmission Lines And Its Applications

Running HVDC and HVAC transmission lines in same corridor or even same tower is an effective way for improving the transmission capability of existing corridor and saving of land resource, and prediction of ion flow field is of great importance, since it determines the height and the corridor width of the hybrid corridor. However, there are problems that makes it difficult to modeling and calculating the ion flow field accurately. By means of numerical simulation and experiments, the present thesis researches several aspects of these problems, such as the spatial and temporal distribution of surface charge density of bundle conductors, the interaction between the HVAC lines and ion flow field of HVDC lines and hybrid field simulation method.To overcome the stability issues of existing ion flow field simulation methods, which usually arising in certain circumstances, the hybrid finite element method finite volume method is proposed in this work. This method combines the advantage of the two methods and solves the governing equations in time domain, which ensures the stability of the method, and thus ensures the reliability of the proposed method when being used in complicate circumstances. This method is then being applied to the calculation of the ion flow field from three HVDC transmission lines running in same corridor, and the ground level ion flow field distribution under different conditions are obtained.The surface charge density distribution on bundle conductor is prerequisite for accurate simulation of ion flow field, however, since direct measurement is impossible until now, the simulation methods are highly depend on experience formulas. This work measured the spatial distribution of ion current around the bundle conductors through a new device, and based on this, the surface charge density distribution on bundle conductor is obtained through numerical simulations.The variation of conductor surface charge density with the AC voltage cycle in hybrid AC/DC corona is the basis for the development of calculation method for hybrid ion flow field. The low frequency current from hybrid AC/DC corona are measured in this work, and a numerical method specially designed for the coaxial experiment device is used to investigate the variation of surface charge density with AC voltage cycles in hybrid AC/DC corona.A new two dimensional hybrid ion flow field simulation method is proposed in this thesis, which is the only method that can makes its calculation result strictly conforms with the Kaptzov’s condition. This new method is then used to research the HVAC lines’corona loss strengthen effect on the HVDC lines and the HVAC lines’ shielding effect on the ion flow field generated by the HVDC lines, which obtained the microscopic mechanism of these two phenomenon that were observed in experiments. To predict the ion flow field under the crossing of the HVDC and HVAC transmission lines, the first three dimensional hybrid field simulation method is proposed in this work. This method is then being used to predicts the changing of the ion flow field distribution with different crossing angles.