Stabilization of power system for large-scaled experimental fusion facility

Abstract In the early experiments of the LHD, the harmful third harmonic currents had been observed in the power line of the NIFS substation, when the fly-wheel motor generator (MG) for the neutral beam injection (NBI) reaccelerates between the plasma productions. The variable harmonic currents, which were estimated to be 1±6 and 1±12 ns, were induced through a Scherbius device. They extremely resonated to the circuit impedance of the power line. To stabilize electrical power in the site, following modifications were conducted: (1) reduction of the harmonic current from the Scherbius device; (2) reconnection of the power supplies of the SC coils and heating devices to suitable power feeders; (3) compensation of lagging reactive power of the MG. As a result, harmful harmonic currents were suppressed.