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

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
$^{\circ}$
) 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.