Study And Calculation On The Electromagnetic Environment Of UHVDC Transmission Line

With the unbalance distribution of the energy and load centers, high voltage direct current(HVDC) transmission technology has a broad development prospects in China. With the development of the economy and increased in need for electricity, existing±500kV Extra HVDC will be unable to meet the requirements, Ultra HVDC±800kV transmission project has been put on the agenda. However, with increased voltage levels, the transmission line environmental effects aroused extensive awareness. The electromagnetic environment of DC transmission lines has been studied much abroad, but the results are mostly in EHV levels. Moreover, it is still nonsystem in China, and can not copy foreign research results directly for the UHV level.The electromagnetic environment of DC transmission lines can be characterized by: DC corona, total electric field, ion current field, radio interference(RI) and audible noise(AN). They are mostly due to the corona of the lines which is closely affected by the distributions of the conductor surface electric field.Firstly, the thesis gives a accurate solution on the surface electric field of bundle conductors by charge simulation method(CSM) with a improved accuracy criteria. Based on the uniqueness theorem, using the uniqueness electric field of the check points as the criteria of CSM which can be reach to any degree of accuracy. A discussion on the simulation charge arrangement principle suitable for the UHVDC model is proposed. The results showed that the method recommend by engineering is unsuitable for 6 and above bundle conductorsSecondly, the thesis gives a discussion on the DC corona current of unipolar lines. Based on the study works abroad, the unipolar lines corona V-I characteristics is computing. The computing method doesn't rely on Kaptzov assumption, because a simple and realistic function that relates conductor surface field to the applied voltage level is incorporated into the analysis. The results are in better agreement with experimental data, and showed that for a unipolar UHV line, the corona loss is 5~8 times to the EHV line and will be more serious for bipolar lines. Thirdly, the thesis gives the computed result of the total electric field, ion current density and ion density, using the method recommended by EPRI of U.S.A. Electrical parameters as well as different seasons and weathers are taken into account. The results showed that the total electric field, ion current density and ion density have consistent distribution rules, increasing the Height of line or the radius of conductors can reduce the total electric field level.Finally, the RI and AN levels of UHVDC are computed, and a discussion about the influence factors of line parameters is proposed. The results showed that, for a UHVDC transmission line, using 6×ACSR-720/50 conductors, with a height above 18m, pole to pole distance above 18m, the total electric field, RI and AN will have the same level of EHVDC transmission lines.