Consideration and research of high voltage insulation strategy for ITER Feeder busbar joint

• Several rounds insulation trials for ITER Feeder joint were carried out in ASIPP.
• Wet-winding, VPI were practiced and attempt for the best impregnation strategy.
• Improvement of wet-winding technology with vacuum assistance was realized.
• To supplement the electrical test, DR technology was explored for insulation quality inspection.

The ITER Feeder busbar joint is an important component which connects different sections of busbar which run from the high temperature superconducting current leads to the magnet terminals. High voltage insulated bus bar sections will be assembled onto the feeder support structure (called the containment duct), and the joints between sections will be made in situ. The high voltage insulation over the joint is the final step to complete the insulation of the whole bus bar system, and its quality is key to achieving the required electrical performance of the system. The final joint has a complex external configuration with an irregular structure in places, which makes it difficult for the application of the insulation. The limited access in the Feeder and the complex joint external structure make the implementation of the joint insulation hard to solve. The Feeder group at ASIPP has carried out significant R&D for the joint insulation, involving research on the selection of materials, the design of the insulation structure, the curing technology and the quality inspection method. After many rounds of manufacturing and testing, the insulation strategy for the Feeder joint will focus on the so-called “wet-winding” technology. Despite the fact that this process has some intrinsic disadvantages, it is more appropriate for the joint structure compared to other methods. The sub-suppliers to ASIPP have chosen this impregnation method for the feeder qualification activities based on guidance from ASIPP. This paper describes the research procedure of the ITER Feeder busbar joint insulation, summarizes the activities on the joint insulation structure design, describes the trials of the impregnation method, and describes the pre-qualification tests. Even for the preferable “wet-winding” process, some improvements have been applied due to recommendations from ITER IO experts. For example, both the use of a vacuum bag during the process and investigation using non-destructive tests (NDT) have been implemented.