Conceptual Design of a Spacer for a 154 kV HTS Apparatus

• Published in: IEEE transactions on applied superconductivity 2019-08, Vol.29 (5), p.1-5
• Main Authors: Lee, Hongseok, Jeong, Minkyung, Jeon, Sangsu, Lee, Onyou, Kang, Hyoungku
• Format: Article
• Language: English
• Subjects: 154 kV superconducting apparatus; Boiling points; Computer simulation; Conceptual design; Condensates; creepage discharge; Cryogenic temperature; Current limiters; Dielectric characteristics; Dielectric strength; Dielectrics; Discharges (electric); Electric field strength; Electric fields; Electrical faults; Electrodes; Epoxy resins; Finite element method; High temperature; High-temperature superconductors; mechanical characteristics; Mechanical properties; Safety factors; spacer; Sparkover; Sulfur hexafluoride; Superconductivity
• ISSN: 1051-8223; 1558-2515
• DOI: 10.1109/TASC.2019.2901597

The termination part of a high temperature superconducting apparatus such as a superconducting fault current limiter or a superconducting cable is usually insulated by pressurized SF 6 gas for its excellent dielectric strength. However, SF 6 condenses into LN 2 because of its high boiling point (approximately 209 K) during operation. The condensed SF 6 into LN 2 may result in problems such as dielectric degradation and system pressure decline. In order to prevent the condensation of SF 6 into LN 2 , the termination of an HTS apparatus is divided into two parts by using a spacer: an upper part pressurized by SF 6 with room temperature and a lower part pressurized by GN 2 with cryogenic temperature. The termination part should be operated in a high-pressure condition in order to ensure safe dielectric characteristics of HTS apparatuses. In this paper, dielectric characteristics as well as mechanical characteristics of a spacer under pressurized gas are conducted. It is well known that electrical breakdown may occur in the form of creepage discharge along the surface of a solid material rather than in the form of penetration sparkover through a solid or gaseous material. Experiments on the creepage discharge characteristics according to several solid materials under various pressures are conducted and a computer simulation using a finite element method is performed to analyze electric field distribution and mechanical strength of a spacer. Finally, the specifications of a spacer for 154 kV superconducting fault current limiters such as diameter, thickness, shape, and material, are suggested according to various safety factors.