A Study on the Thermal Characteristics of the Epoxy Insulator in the Stop Joint Box of HTS Power Cable

AbstractThe HTS power cable is cooled by the circulation of liquid nitrogen. The cooling capacity of refrigerator increases with cable length. As the length of power cable increases, a joint box should be installed to reduce the cooling capacity and pressure drop for unit cooling system. The type of joint box can be divided into two groups. There are NJB(Normal Joint Box) and SJB(Stop Joint Box). Generally, SJB can separate each cooling system. In case of long distance DC cable, it is necessary to separate the cooling line in the regular distance of cooling system so SJB should be used. However, SJB, which has a difference from the insulation method of existing joint box, uses solid electrical insulation method. At the primary cooling time, thermal stress is generated by the temperature difference between the internal and external epoxy. So to prevent the damage stress analysis is required for the electrical insulation structure of SJB. In this paper, using the FEM analysis we study the cooling method and optimal shape of SJB to reduce the thermal stress result from temperature difference during the cooling time

A Study on the Electrical Contact Resistance and Thermal Conductivity of Soldered-Metal Insulation Coil With Conduction Cooling

The no-insulation (NI) winding method has been widely used in the fabrication of superconducting coils owing to its excellent thermal stability and mechanical stiffness. In the NI coil, there is a charging delay and heat loss due to leakage current. Therefore, the metal insulated (MI) winding method was proposed to reduce the charging delay and the heat loss due to the leakage current and the increased contact resistance by the metal tape. However, it is difficult to quantify the contact resistance between the turns of the coil during the design stage. To resolve this problem, a new winding method, called soldered metal insulation (SMI), was proposed by the authors, and the electrical properties were evaluated in a bath of liquid nitrogen. As a follow-up to the previous research, experimental investigations were conducted in a conduction cooling test apparatus to investigate the electrical and thermal characteristics of the SMI coil below 77 K. The electric contact resistances were evaluated through sudden discharge experiments. Then, the thermal contact resistances were measured using a heater installed on the outer turn of the coil. It is believed that the SMI winding technique can be applied to fabricate rare-earth barium copper oxide (REBCO) coils with predictable electrical and thermal contact resistances.N

Investigation of the over current characteristics of HTS tapes considering the application for HTS power devices

High temperature superconductor (HTS) is developed for applications in HTS power devices such as power transmission cable, transformers, superconducting fault current limiter (SFCL), motor, and generators. HTS power devices applied in power systems might undergo over current, such as over load, fault conditions, and unbalanced current. The electrical characteristic analyses of Bi2Ca2Sr2Cu3Ox (Bi-2223) HTS tapes and YBa2Cu3Ox (YBCO) tapes are very important for the application of HTS power devices. In this study, the transient phenomenon of HTS tapes was analyzed when the DC over current as well as the AC over current flow. Also, the experimental results of breakdown cycle, variation of temperature and resistance according to fault current in HTS tapes were analyzed. These results would be very significant data and give good information in order to design and fabricate HTS power devices. © 2008 IEEE