Theoretical Study on Capturing the Separation Interface of Out-of-step Based on Reactive Power

The characteristics of electrical parameters of separation interface are discussed when an equivalent two-machine power system is out-of-step. While a multi-machine system is out-of-step and splits into two coherent groups, the separation interface, generally composed of several tie-lines, will disconnect the whole transmission network into two coherent electrical islands. The characteristics of the separation interface tie-lines are as follows. First, the active power flow crosses zero and oscillates periodically. Secondly, there is one point, the center of out-of-step, existing in the interconnector whose voltage amplitude change is the largest when compared with those of other points, viz. a large voltage gradient in separation interface occurs during the course of out-of-step. Thirdly, reactive power flows from both sides to the interior of the separation interface. The integral value of reactive power in one period of out-of-step reflects the characteristics of separation interface by adopting the first characteristic above. Thus the reactive power based method of capturing separation interface is presented.