A Fast Recognition Method Of Coherent Generators Based On Wide Area Information

The modern power system is becoming increasingly complex and the installed capacity of electrical power system is also growing.Both of them make it more and more important to keep the network stable and surveillance as well as control of the network.The power system is walking towards the real-time dynamic monitoring and control direction.With the region interconnected of the power grid,region interconnected power grid between electrical contacts gradually strengthens,the operation is becoming complicated and changeable and the power grid's dynamic security problems have become increasing critical.So how to ensure safe and stable operation of the power system and avoid chain accident and large power failure accidents is of great significant.Auto-disconnection is the third line of defense to power system.It is of great importance to avoid cascading failure of power grid and power failure accident for the power system.The fast and accurate identification of the coherent generators is the first step of power system out-of-step separation.Besides,when disturbances happens in the power system,identifying the coherent generators and uniting them into an equivalent generators can simplify the power system and decreasing the amount of computing.In a word,the fast and accurate identification of coherent generators is of great significance for the power system.The coherent generators recognition method based on wide area measurement system(WAMS)is a vital method among the coherent generators recognition method based on generators disturbed trajectory methods.The Phase Measurement Unit(PMU)is the bottom measurement unit of WAMS.Then the communication system transmits the measured data to the higher level,data collector,in real time.After a certain data processing,the system achieves the dynamic monitoring of power system running and other advanced functions.It makes it possible of the real time operation and control of power system.The generators' disturbed trajectory contains all the factors that influence the coherence between generators.According to the information of generators swing curves to obtain the coherence of generators is more accurate.Considering that rotors angular acceleration of the generators is the root cause of rotors angle' change,this paper firstly calculates the angular acceleration of the generator' rotor obtained by the difference method of the measured value of WAMS.Then generators with the same angular acceleration curves of the generator zoned into the same coherent group.Corner curve preserves important feature information of the curves.So in the judgment of angular acceleration curve similarity,the paper judge the similarity of angular acceleration curve according to the differences of amplitude and phase comparison angle point.to achieve the initial clustering of the system.Wide Area Measurement System(WAMS)provides an effective platform for the automation of power system.In this paper,a new method based on the power angle information from WAMS is proposed.Firstly it calculates the rotors' angular velocity and angular acceleration using the second-order algorithm.Then through the extraction and comparison methods of corners in the coherent clustering algorithm and comparison of the amplitude and time differences it obtains the preliminary coherent generators identification result.Finally,discrete Hausdorff distances of rotors' angular velocity construct the undirected graph of coherent generators and the Graph-theoretical Clustering theory realizes the precise coherent generators identification.This method is simple and adaptive data window makes clustering rapid.It is very suitable to complex interconnected power grid.In this paper,the EPRI-36 bus system simulation example verifies the correctness of this method.