DC Ultrahigh Voltage Insulation Technology for 1 MV Power Supply System for Fusion Application

To realize dc 1 MV power supply system for neutral beam injector in ITER, long-pulse dc ultrahigh-voltage (HV) insulation technologies have been developed. For a dc 1 MV insulating transformer, a composite bushing has been newly developed to overcome the manufacturing difficulty of a conventional condenser bushing (CB). The composite bushing has a small-sized CB and fiber reinforced plastic tube to sustain 1 MV stably inside and outside of the bushing. The mock-up of the insulating transformer has fulfilled the ITER requirement of dc 1.2 MV insulation for 3600 s. An HV bushing to transmit multiple voltages simultaneously has also been developed through a careful experimental study on vacuum insulation characteristics with multiple gaps between large electrodes. It has been found that the voltage holding is dominated not by number of the electrodes but by a total cathode surface area of electrodes. Based on this result, the vacuum insulation inside the HV bushing with five electrostatic screens has been designed to realize a stable vacuum insulation of 1 MV.