The authors suppose an interconnecting system between a commercial scale closed cycle MHD combined generation plant and power grid, in which a disk MHD generator using cesium seeded helium plasma and a synchronous generator are connected in parallel to an infinite bus through a common power transmission line, and perform detailed numerical simulations of the transient behavior of the whole system. It is made clear that the transient stability of the closed cycle disk MHD generator using cesium seeded helium plasma is excellent under the power line fault condition, even in the case where the generator is commercial scale and is connected to the power grid in parallel with a synchronous generator. It is also made clear that the effectiveness of the control method for power system stabilization using the fast power control of the MHD generator recently proposed by the authors is sufficient in the case where the working plasma of the MHD generator is cesium seeded helium because the transient stability of the MHD generator is always maintained and the transient rotor angle swing of the synchronous generator is notably suppressed. (C) 2003 Elsevier Ltd. All rights reserved.