A predictive out-of-step protection system based on observation of the phase difference between substations

A recently developed predictive out-of-step protection system is described. The purpose of this protection system is to prevent total system collapse caused by step-out between large-capacity generator groups due to a serious fault in the trunk transmission line. This is accomplished by using online data collected during the incubation phase to predict a step-out and then issuing a system-seperation command. The system has the following characteristics: (1) the phase difference between several large generator groups is measured from online voltage data collected from substation busbars in the vicinity of the generators at a sampling rate of 600 Hz: (2) the phase difference at 200 ms in the future is predicted from the measured phase-difference data; and (3) if the predicted phase difference exceeds the instability threshold value, system separation if performed taking into account the power supply and demand balance after tripping