Development of Insulation Technology With Vacuum-Pressure-Impregnation (VPI) for ITER Correction Coil

Abstract

ITER Magnet System includes 18 Correction Coils (CC), made with NbTi cable-in-conduit 10 kA conductor, wound into multiple pancakes. The turn and ground insulation were electrically insulated with a glass tape/polyimide interleaved multilayer composite, which should be impregnated with epoxy resin. Some technical issues remaining have to be addressed in the manufacturing process of these coils. One of the issues is the impregnation and curing of the insulation system, which should achieve good mechanical properties and sufficient high voltage insulation (5 kV). The authors performed manufacturing trials of the insulation system using the vacuum pressure impregnation (VPI) method, which is an effective process to remove defects such as dry spots and over rich resins in the insulation system. In order to simulate and optimize the feasible VPI process, two VPI test samples with the length of 1000 mm have been fabricated. In this paper, we introduce the detailed VPI process including the insulation materials and insulation structures for CC and present the results of the related mechanical and electrical tests performed. The mechanical properties, including tensile strength, inter-laminar shear as well as compressive shear (45 ) were evaluated at room temperature and liquid nitrogen temperature (77 K). In addition, the dielectric strength of the turn insulation and the ground insulation on the test samples were also examined. The results of the tests were discussed versus the design requirements.Index Terms-Insulation, ITER, mechanical and electrical properties, vacuum pressure impregnation.

Design and Analysis on Electric Performance of Threaded adhesive joints of composite Axial Insulation Break

“…The electric field strength distribution along S, L1, L2, and L3 path are shown in from Fig.4 to Fig.7. It is evident that the maximal value of electric field strength for insulation break is 3.396kV/mm in Fig.4 and Fig.5, the maximal value of electric field strength along the outer interface between air medium and GFRP section is 1.231kV/mm from Fig.6, and the maximal value of electric field strength along the surface of inner insulation pipe is 1.271kV/mm from Fig.7, but the maximal value of electric field strength along the axial line of inner insulation pipe in air is only 1.203kV/mm [5]. …”

Mechanical property tests on structural materials for ITER magnet system at low temperatures in China

“…The schematic diagram and real picture of clamp for shear/compression test are shown in FIGURE 6(a) and FIGURE 6(b), respectively. Test results indicate that mechanical properties of the insulation material of the ITER CCs meet the ITER IO requirements [20]. …”

“…Both the geometry of sub-size tensile sample and test procedure are similar to those of the TF conductor jacket material respectively. [20]. Tensile tests were conducted at 77 K with a double-bell specimen [20].…”

“…[20]. Tensile tests were conducted at 77 K with a double-bell specimen [20]. The standard ASTM D 3039 was developed to evaluate tensile properties of discontinuous fiber or discontinuous fiber reinforced composites with a rectangular sample.…”

Research on Adhesive Joints of Low-temperature composite Axial Insulation Break

“…The breaks consist essentially of an insulated tube between the two steel tubes inserted into the steel cryogenic line. The outer surface has a metal screen which is integrated into the ground screen of the high voltage cryogenic line, and there is metal reinforcing of both the insulating part, particularly where it overlaps the steel tubes to form a bond [3]. There length must be sufficient to prevent electrical breakdown between the two steel tubes through the fluid or gas.…”