274 / 2018-09-25 11:04:06

Electrothermal coupling simulation of terminal insulation of superconducting DC energy pipeline

simiulation,electrical insulation,extreme condition

Superconducting DC energy pipeline realizes the mixed transportation of electric energy and liquid natural gas. It is a high efficiency and low energy consumption way of redistribution of energy. The superconducting DC energy pipeline terminal is one of the core equipments of superconducting DC energy pipelines which bears various extreme conditions such as electric field, low temperature, mechanical stress, etc. Under the influences of multiple physics, the electrical and thermal properties of the terminal materials will change to varying degrees, and these changes will cause distortion of the physical field in turn, especially under the extreme conditions like superconducting operation environment. Therefore, in the design of the terminal structure, multiple physical interactions and mutual cooperation methods need to be considered. In this paper, under the two-way coupling of multi-physics and terminal material parameters, the physical simulation model of superconducting energy pipeline is established, and the electric field distortion and local overheating phenomenon generated in the simulation model are analyzed. This study provides theoretical support for the insulation optimization design of superconducting energy pipeline terminals.
In this article, a physical model of superconducting energy pipeline terminal is established by COMSOL. According to the existing experimental results, the function of the different parameters (such as conductivity, dielectric loss, etc.) changing under physical fields was fitted in various materials. Under the operating conditions of 100kV/1kA, the temperature distribution and changes of conductivity of different materials was studied. Then, the distribution of the radial electric field and axial electric field of the terminal under dynamic temperature was analyzed. Furthermore, we changed the thickness of the insulating material, the liquid nitrogen cooling power and other conditions to study how these changes influenced the distribution of electric field and thermal field.
First, we found that the distribution of terminal temperature determines the distribution of material conductivity. Even in a same material in same area, there will be an order of magnitude difference in conductivity, which leads distortion of electric field and thermal field. Second, the distribution of conductivity has a great influence on the axial distribution of the electric field in the material of the terminal insulating material which may leads flashover on the surface of bushing. But it has no significant influence on the radial electric field distribution. At last, the leak heat of bushing and Joule heat generated by the current lead are the main reasons of the temperature raising of the terminal. And with the cooling power of liquid nitrogen raises, the temperature gradient of the terminal is obviously reduced. However, raising the cooling power means more energy consumption.
The change rule of the material conductivity with temperature counts a great deal in the distribution of the electric field thermal field in the terminal. At the same time, the cooling power of liquid nitrogen influences the temperature distribution, thus affect the electric field indirectly to a certain extent. Therefore, in the optimization design of the terminal, selection of insulation materials and how to control the terminal heat leakage should take into consideration.