The output active power of the generator is determined by the air intake of the steam turbine. When the generator and the system are connected to the grid, the active power output of the generator increases by increasing the air intake through the steam turbine synchronizer, and vice versa. When the generator is not connected to the grid, the steam turbine synchronizer increases the air intake, and the output frequency of the generator increases, and vice versa. At this time, the output active power does not change, because the active power of the generator is determined by the load it carries. When the generator and the system are connected to the grid, the adjustment of excitation current is based on the voltage, power factor and generator operating current of the whole plant at that time. For example, when the power factor of the whole plant is lower than the value specified by the electric power department, when the current of the generator and exciter does not exceed the rated value and the voltage is not higher than the specified value, the excitation current can be increased to increase the reactive power output of the generator and improve the power factor of the whole plant (at this time, the power factor of the generator will be lower).