Study On The Out-of-step Identification And Islanding Strategy Based On PMU Data

With the power system interconnection basically formed in our country, allocation of resources can be optimized in wider area and power urgent support under accident condition is easier to be provided. Nevertheless, if the out-of-step situation caused by a sudden failure is dealt with improper operation, bringing to the spreading of the accident, large scale and long time blackout will be caused, and a huge economic loss will be the price in the end. When the emergency control measures can not contain the disaster spreading, it is of capital importance to identify loss of stability of the power angle and disconnect the system at reasonable places rapidly and accurately. According to the real-time synchronized trajectories that PMU can provide, the author firstly induces the characteristics that the genenorators'energy trajectories perform under COI coordinate system, and proposes the concept of"Double-Energy"function which represents kinetic energy and potential energy. Formula derivation proves that the criterion can identify step out fleetly of one generator to the whole COI system. At the same time, this paper studies a method to judge coherence groups based on the velocity of variation of generators' spindle speed, which can be calculated after PMU does the data acquisition. Through depicting and fitting the acceleration, values that represent the level of similarity between the fitted curves of each generator can be listed every fitting cycle. Coherence groups are distinguished through the work that done above. This method can distinguish the coherence groups apart accurately, shortly after the out-of-step identification criterion takes action. The two of them can cooperate with each other efficiently, which make preparations for the splitting strategy. Finally, according to the result that obtained from the first two parts, this article uses the way of graph contraction acceleration to capture dynamic separation interface. Simulation work based on the IEEE-9 and IEEE-39 systems proves that the criterion can promptly identify step out accurately, and islanding plan based on the coherence groups can be formed. This paper brings forward a rapid and accurate way to solve out-of-step and islanding problems. The whole strategy is realized with MATLAB program.