Development of the 120 kV/70 A high voltage switching system with MOSFETs operated by simple gate control unit

A 120 kV/70 A high voltage switching system has been installed at Korea Atomic Energy Research Institute in Taejon to supply power to Koma Superconducting Tokamak Advanced Research (KSTAR) Neutral Beam Injection (NBI) system. The NBI system requires fast cutoff of the power supply voltage for protection of the grid when an arc is detected and fast turn-on of the voltage for sustaining the beam current Therefore the high voltage switch and arc current detection circuit are important parts of the NBI power supply systems and there is much need for high voltage solid-state-switches in NBI system and a broad area of pulse power applications. To get a high voltage switch, the series-connection of a semiconductor device is usually used. The main problems in such high voltage switches are to guarantee the voltage balance across the device and isolate the bias power supply and gating signals from the hot line. This switch consisted of 100 series-connected power MOSFETs and adopted the proposed simple and reliable gate drive circuit without bias supply. The arc current detection circuit, which used the Pearson CT and Hall CT, makes it possible to detect the arc. So the reliability for long term in industrial use and low price have been accomplished in this system. Various results taken during the commissioning phase with a 1.7 kΩ/100 kW resistive load. This paper presents the detailed design of 120 kV/70 A high voltage MOSFET switch and simple gate drive circuit. Problems with the high voltage switch and gate driver and solutions are also presented.