Research On Coordination Of Inverse-time Overcurrent Relays Towards Different Topologies

Due to the simple implementation,low cost,and natural coordination,the directional overcurrent relays(DOCRs)are increasingly used widely in China’s power grids.With the acceleration of the new generation of energy systems evolution and the gradual formation of cross-region interconnected large power grid configuration patterns,modern power systems have become more flexible in operation and have more diverse power network topologies.The new development of the power system has put forward higher requirements for the coordination of DOCRs.The DOCR coordination problem under different network topologies has become a research hotspot.For this reason,this paper focuses on the research on coordination of inversetime DOCRs under different topologies of the power grid.The main research work and contributions are summarized as follows:A novel strategy for optimal coordination of DOCRs under different topologies based on topology grouping and equivalence is proposed.This strategy starts with the idea of model constraint-dimensionality reduction.It aims to solve the problem that massive inequality constraints make it difficult or even impossible to solve the model when the large scale power system takes into account different network topologies.The network topology description model of power grids used for relay setting calculations is studied,and different network topologies are grouped based on the aggregation hierarchical clustering algorithm.The equivalent representative topology calculation method based on the similarity of topological trajectories is proposed.The model based on the equivalent representative topology is established for optimal coordination of DOCRs.The results of case studies show that the proposed strategy comprehensively considers different network topologies and improves the relay adaptability to different topologies.Moreover,it also effectively reduces the constraint dimension and facilitates the existing methods to determine the optimal relay settings towards different network topologies.A novel scheme for DOCRs adaptive coordination with the optimal configuration of setting groups(SGs)under different topologies is presented.It originates from the concept of adaptive protection and aims to improve the relay maintainability of DOCR confronting grid topology changes.The optimal coordination model for DOCRs with adaptive numbers of SGs under different topologies is established.Based on the fault current characteristics in the network,the evaluation indicators of relay adaptability to different topologies are proposed.An iterative method is used to determine the adaptive numbers of SGs and corresponding settings for each relay,and then the online application strategy is presented.The results of case studies show that the proposed scheme effectively improves the relay maintainability,while it ensures that the obtained relay setting performance meets the requirements of different topological operations with satisfaction.A novel method for multi-objective optimal coordination of DOCRs considering network topological uncertainties is advanced.From the perspective of uncertainty analysis,this method aims to improve the overall adaptability of protection to different topologies of the power grid.The problem of probabilistic modeling for different network topology considering uncertainties is studied.A multi-objective optimal-probabilistic coordination model for DOCRs by fasting relay operating time and minimizing the miscoordination probability of primary/backup relay pairs under all topologies is proposed.The multi-objective particle swarm algorithm is used to obtained multiple sets of relay settings from the Pareto optimal solution.The results of case studies show that the proposed method can improve the protection tackling ability to different network topologies on the premise of ensuring the minimum probability of missing selectivity between the primary/backup relay pairs in the network.Additionally,the method can also provide a comprehensive and reasonable choice of the optimal relay setting between speediness and selectivity of DOCRs.