a generating system having a rotating type generator to interconnect a power system in order to output power of the generator to the power system comprises a generator , an exciting circuit and an excitation control section . it also comprises short - cycle stabilizing sections for outputting a short - cycle stabilizing signal for suppressing short - cycle power fluctuations according to at least one of an electric parameter and a mechanical parameter of the generator and a long - cycle stabilizing section for outputting a long - cycle stabilizing signal for suppressing long - cycle power fluctuations having a cycle time longer than short - cycle power fluctuations according to the mechanical parameter of the generator . the outputs of the short - cycle stabilizing sections and the long - cycle stabilizing section are sent to the excitation control section .