A Method Of On-line Recognition Of Coherent Generators And New Scheme For Out-of-Step Spliting

Along with the constant enlargement of the interconnection of the large area power net scale, the issue of dynamic security and stability become increasingly serious, out of step and cascading trip caused by failure would cause immensurable damage to the entire grid. It is imminent to strengthen and improve the building of the power system security and stability “three lines of defense”. As an important measure of ensure the safe operation, splitting is last defensive line to prevent the collapse of the entire system, and it has been widely used in the state grid. As the last defensive line to ensure the security and stability operation of power system, splitting control can effectively prevent further expansion of the failure. The coherency identification of generator in the system is an important prerequisite for splitting control, it has important significance on the simplifying process analysis and recovering synchronous operation quickly.With the emergence of wide area measurement system and the development of communication technology, the research for coherency identification and splitting sparkle new activity. Based on wide area information, the paper focuses on two issues for further study: 1. Propose a new method for coherency identification which can group fast and effectively; 2. Put forward a new scheme for splitting control which is not affected by the change of system operation mode and structure.A new method enable to online recognize coherent generators in power system is proposed. Introducing the discrete Fréchet distance into online coherency identification of generators, and the information demanded is the real-time values of generator power-angle measured by wide area system. Firstly, the sample power-angle values are fitted by trigonometric function to attain the primary result of coherency identification; and then the final result of coherency identification is achieved by calculating the discrete Fréchet distance. Compared with the existing methods, the proposed method is simple and clear and its calculated amount is smaller, so the dynamic online clustering of coherent generators can be implemented and it is suitable to complex interconnected power grid especially.Then we focus on the influence of unequal voltage amplitude and the change in the operation conditions of power system on oscillation center and out-of-step center when system desynchronize. Oscillation center position function is constructed and a new scheme for out-of-step splitting is proposed. Firstly ucos? and oscillation center position function change rate are applied to start the splitting device. Then the movement characteristics of oscillation center, the position of out-of-step center and the island unbalanced degree are comprehensively considered to search the splitting surfaces. The proposed scheme can distinguish synchronous oscillation from out-of-step oscillation, capture the movement of oscillation center and the position of center of out-of-step and avoid the impact of system operation change and network structure change.