The nominal field strength calculation of UHVDC transmission lines based on surface charge method

China is a vast country, the economic development and resource distribution is extremely uneven. The development of ultra high voltage direct current (UHVDC) transmission can help achieve optimal allocation of resources and supply of energy across the country. UHVDC transmission is widely used in China for its unique advantages based on China´s actual situation, but the attendant electromagnetic environmental problems caused by the transmission lines caused people´s attention. Therefore, the theoretical estimation and analysis of electromagnetic environment surrounding UHVDC transmission line has important theoretical and practical significance. Since the nominal electric field is an important component of the synthetic electric field, the nominal field strength can be used as reference for ground electric field. Methods of calculating the nominal field strength below the transmission lines, mainly include charge simulation method, surface charge method, finite element method, and so on. On the basis of a comprehensive comparison of various electric field calculation methods and combine with the feature that UHVDC transmission line with multiple bundled conductors, using field surface charge method to calculate the distribution of nominal field. In this paper, by the example of Xiangjiaba-Shanghai ±800kV UHVDC, which adopt bipolar six-split transmission lines, the basic principles and the calculation steps of the surface charge method are introduced, the electric field model of the UHVDC transmission lines are established by using Matlab software. And the conductor surface charge density of each node can be calculated by the surface charge method, then the potential and electric field strength of any point under the transmission line can be calculated. Compared with calculation of charge simulation method shows that the surface charge method can calculate the distribution of the nominal field strength under the UHVDC transmission line can be more accurate- the results show that compared with the charge simulation method accuracy will increase and since the simulation charge position needn´t adjust, computation time has been reduced.