Abstract: Voltage, current and field voltage of a generator connected to an electric power system are sampled at a predetermined period for analog-digital conversion and then led to a digital computer. In addition to computation for AVR, the computer computes from its input the generator output power, and also monitors the occurrence of a fault, the removal of the fault and variation in the generator output in the system. After the occurrence of a fault, the field excitation of the generator is intensified until the generator output power reaches substantially a peak value, but after the peak value is substantially passed by, the excitation is conversely depressed to a value below the level which is present before the fault occurs. When the generator output power recovers the value which is present before the fault occurs, the computer returns to deliver the AVR output.