[en] The design study for JT-60SA (Super Advanced) has been just started as the next generation device of JT-60. The longer pulse operation is required for the additional heating facilities of NBI (Neutral Beam Injector) and RF (Radio Frequency) systems. Since the pulse length of the additional heating facilities in JT-60SA is 100s and longer, a new AC power system has to be developed for direct connection to the commercial power grid to cover the insufficient energy from the 3 motor generators. In this report, we propose a new AC power system for JT-60SA, and present the design study of the reactive power compensator including high harmonic current filters and shunt capacitors using the 'PSCAD/EMTDC' simulation code. In addition, the design study of a load adjusting system to suppress large voltage fluctuation to the commercial power grid is also provided. (author)