Progress of ITER Feeder System Electrical Insulation Qualification

The ITER Feeder is an important subsystem, which transmits the electrical power to the ITER Tokamak magnet system. In the Feeder, all the HV potential components, including the current leads, the busbars, and the joints, need to be insulated with solid composite materials to electrically isolate the HV potential from ground. Based on over three years of preliminary qualification and experimental comparison, the prepreg tape and relevant curing techniques were finally chosen as the formal feeder insulation material and method. The formal insulation qualification was launched, including the material qualification and the component qualification. Now the static tensile/shear strength, the fatigue tensile strength, the compression-shear strength, the push-out strength and the void content test for the prepreg material qualification has been completed. This paper describes the whole research improvement of ITER feeder electrical insulation qualification activities, introduces the selection of procured materials and the manufacturing trials, and summarizes the formal qualification items and their test results.

I. Introduction

The ITER Feeder system is an important sub-system for the ITER superconducting Tokamak, it transmits the electrical power, conveys the cryogenic coolant and carries the instrumentation wires to the magnet system. In the feeder system, there are total 26 feeders supplying the electric current to 48 superconducting coils (18 Toroidal Field coils, 6 Poloidal Field coils, 6 Central Solenoid modules, 18 Correction Coils) [1]. Using the current leads, the sectional busbars, and the twin-box type joints, the feeders connect the terminals of coils to the power suppliers, each feeder has 2 pairs or more busbar systems (includes the sectional busbars, the current leads, and the joints), which shall be designed based on the same electric parameters as the coils. The busbar system must withstand the maximum voltage to 30 kV under the magnet fault condition. In order to prevent arcing and flash over accidents across the parts in the feeder, the busbar system needs to be electrically insulated also against the Paschen discharge [2]. Meanwhile, the electrical insulation shall withstand the largest Lorentz force up to 60 kN/m [3] and survive the stresses during the machine warming up and cooling down cycles.