The High Power Dual Brayton Test Rig at NASA Glenn Research Center (GRC) is a uniquely configured power conversion system built around two modified commerical Capstone C-30 microturbines and employs two closed-Brayton-cycle (CBC) loops sharing a common gas inventory and heat source. Because both Brayton loops share the gas inventory, the operation of one Brayton affects the performance of the other Brayton, especially when one Brayton is in standby or spinning at a different shaft speed. System operating scenarios consist of the Braytons at equal or unequal shaft speeds; one Brayton operating while the other is either in standby, system startup, or shutdown. Steady-state tests consisted of multiple turbine inlet temperatures and multiple shaft speeds to provide a system performance map. Although the hardware is not intended to represent a flight-like system, the insight gained from operating this unique power conversion system will provide useful information for future development of Brayton systems.