| In recent years, the DC transmission technology is developing rapidly in China. Due to the special national conditions, the EHV and UHV DC transmission has taken the leading position in the world. However, most of the UHV DC transmission projects in China are located in the high-altitude and large-vertical-drop area or in the mountains in harsh weather conditions, where the geographic, cultural, climatic and meteorological conditions are complex and changeable, thus it makes the transmission line corridor selection, the lines repair and maintenance and the converter station equipment connections much more difficult while the traditional overhead transmission lines, high voltage DC cable and bushing can hardly solve these problems. Besides, the lead of the large-scale power plant and the large city power grids also need a kind of transmission line featured with large capacity, environmental compatibility and stable operation. The gas-insulated transmission line, short for GIL, has the unique advantages can solve the problem well. The mature GIL products have been widely used in the field of high voltage AC transmission, of which the security and stability also have been verified.In order to speed up the development of the DC GIL and make it as soon as possible for engineering application, the DC GIL insulation characteristics test platform was established in this paper to do the research on the insulating properties of the SF6gas-gap and the GIL insulator under the DC stress meanwhile the influencing factors of the insulating properties has also been studied. The paper firstly gave a brief introduction to the classic gas discharge theory in the coaxial cylindrical electrode gap. Then the influences of pressure, voltage polarity, the electrode shape, electrode surface roughness, the conductive metal particles and humidity on the SF6gas-gap breakdown characteristics were researched on the basis of the test platform. The UHVDC GIL test unit was taken into use to test the breakdown characteristics of the long SF6gas-gap under DC non-uniform field. A static conductive metal particle was attached on the surface of the insulator model and then the flash-over test was carried out, in this way the relationship between the metal particles and the insulator flash-over properties was studied. The long-term DC withstand test was taken on the disc insulator, and the test result reveals the impact of the surface charge accumulation on the insulator flash-over characteristics. Three-dimensional simulation model of a disc insulator and a column insulator was built to calculate the DC electric field distribution on the insulator surface and also the space electric field around the insulator by using the finite element analysis method. The method and requirements of the insulation performance evaluation test to the UHVDC GIL unit was also proposed in the paper.The results obtained in this paper can be applied to the DC GIL insulation structure design, the electric field distribution optimization as well as the test, evaluation, operating management of the DC GIL products, which provides a technical support to the research and engineering applications of the DC GIL... |
PDF Full Text Request