Study on improved out-of-step splitting criterion based on the PMU

U cosφ out-of-step criterion was studied in this paper. It is found that U cosφ criterion can only partially capture the variation of the oscillation center voltage, so a method using PMU devices to measure both ends of the bus voltage phase angle difference as a secondary criterion combined with U cosφ criterion is proposed to locate of step oscillation center accurately. equivalent two-machine system model is established to verify the out-of-step based on both ends of the bus voltage phase angle difference by PSCAD simulation tools. The results show that the method can take advantage of the multiport measurement to recognize the out-of-step system state timely so that the contact line can be break reasonably and quickly.