Study On Calculation Method Of Electric Field Around ±800kV UHVDC Lines

Maxi-surface electrical field of the bundle lines is the important gist on deciding the layout and dimension of the UHVDC lines, and the nominal field is one of the most important indexes on evaluating the impact on the environment from the UHVDC lines. As the Yung-Guang±800kV UHVDC projects start continuously, the study on the methods of calculating the electric field around the lines is being more important and significative. Combined with the trait of the bundle lines, the model of calculating the electric field around the lines is ameliorated, and the use of optimized charge simulation method, compensated charge method, multi-charge method and finite element extrapolation method in the calculation of electric field is studiedin this paper. And, the electric field around the lines is calculated based on the charge simulation method and finite elements method. In addition, the choice of the lines and shield lines is calculated and analysised. According to the results, we got conclusion as follows:(1)Based on the principle of the optimized charge simulation method, the optimized charge is used to calculate the electric field around the lines. During calculation, the offset distance of the simulation charge is set as the variable of the objective function, and the restrictive problem is transformed into a non-restrictive one, golden section method is quoted to set the simulation charge in the optimal position, and now the charges supersede the lines accurately.(2)In the compensated charge method, the potential error of the points on the line's surface is compared constantly, and the charges are moved in the designed direction in order to reduce the maximal potential error and decrease the inhomogeneity of the line's surface potential. Finally, another point at which the potential error is the same as the maximal value appears. Now, the maximal potential error reduce to the end, and the electric field is precise.(3)Multi-charge method, which is improved from split charge method, divides one sub-conductor into many regions, and set a charge in each region, so the consecutive charges are replaced by many independent ones. As a result, the equivalence error is reduced. This method has a simple principle, and high precision, but needs more computing time.(4)Finite element method is used to calculate the electric field around the lines, the discretion error is reduced by self-adaptive mesh partition and mesh re-partition, the error caused by edge sealing is employed to reduce the by using FEM extrapolation to deal with the data.(5)The impact of shield lines on the model is also discussed. We find that the shield lines shouldn't be neglected. The polarity of the simulation charge in the shield lines is opposite to that of the charges in the transmission lines, which cause the aberrance of surface electric field, makes the maximal electric field stronger and the nominal electric field weaker.(6)Combined with Yung-Guang UHVDC lines, the surface electric field of the shield lines and it's influencing factors are compared when they are grounded or not. It is found that the electric field is strong, when the shield lines are grounded. And it is affected by the dimension of the shield line, the angle of protection and the height to ground. When the shield lines are not grounded, the electric field is much more less, and it is decided by the angle of protection and the height to ground. But now, there is a certain potential in the shield lines.(7)Surface electric field is calculated when the lines in different bundle forms. The result shows that among the factors deciding the electric field, the dimension of the lines and the split number are more effective than the the split distance and the anode-cathode distance, and the height to ground has little influence.