Dielectric characteristics of gaseous helium (GHe) injected into the cooling system to make sub-cooled nitrogen condition with constant pressure is found to be extraordinarily weak in dielectric strength . In high voltage superconducting machines using the sub-cooled nitrogen cooling system, the current lead part in GHe environment could be electrical weak points rather than the superconducting magnet part in liquid nitrogen (LN2). In order to enhance dielectric characteristics of current lead part, three methods are suggested in this paper. The first one is enclosing the current leads with solid dielectric material and the second is exposing the current leads to high vacuum, and the last is topping up the magnet system with dielectric materials such as Glass Bubbles (GB) which is usually used as heat insulator. In addition, the extinction time of bubbles caused by the electrical breakdown is measured to determine the suitable pressure of sub-cooled nitrogen system. It is found that the characteristics of bubble extinction in LN2 are drastically enhanced over 1 bar.
Bibliographical noteFunding Information:
Manuscript received August 27, 2006. This work was supported by a grant from Center for Applied Superconductivity Technology of the 21st Century Frontier R&D Program funded by the Ministry of Science and Technology, Republic of Korea. H. Kang, C. Lee, and B.-Y. Seok are with the Electro-Mechanical Research Institute of Hyundai Heavy Industries Co. Ltd., Gyeonggi-do, Korea (e-mail: firstname.lastname@example.org). T. K. Ko is with the Dept. of Electrical and Electronic Engineering, Yonsei University, Seoul, Korea. Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/TASC.2007.898047
All Science Journal Classification (ASJC) codes
- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics
- Electrical and Electronic Engineering