Research on the distributed capacitance for high-voltage key components on CRAFT NNBI

The negative ion based neutral beam injector (NNBI) with a beam energy of 400 keV is one of the subsystems of the comprehensive research facility for fusion technology (CRAFT) of China. The distributed capacitance of high-voltage components is an important basis for the design of surge suppression devices of CRAFT NNBI. This study conducted calculations of distributed capacitance for the key components, including high-voltage deck, transmission line, and isolation transformer in the power supply system using the finite element method. The relationship between high-voltage deck (HVD) distributed capacitance and the distance from the wall was discussed. The differences in distributed capacitance and energy storage between non-coaxial and coaxial transmission lines were also debated. Finally, the capacitance between the primary and secondary windings of the –400 kV isolation transformer, as well as between the secondary winding and the oil tank casing, was calculated.