Research Of Crucial Techniques On Relay Protection Coordination And Fault Disposing For Distribution Systems

Distribution Automation is an important part of the Smart grid. It’s of great significancefor improving the reliability of power supply, expanding power supply capacity and toachieve efficient and economic operation of the grid. Automated fault section location,isolation and restoration is one of the key content of Distribution Automation.To coordinate the relay protection with the Distribution Automation System (DAS), theprobability and strategy of multi-grade protection are discussed in this paper. Fortime-grading cooperation depending on time delay, the approaches are divided into twoclasses according to different operation mechanisms, driving technology and fault detectionalgorithms. The fault allocation and restoration modes based on relay protection anddistribution automation are discussed. The setting principles of two-grade time-gradingprotection and three-grade time-grading protection are suggested. The hybrid approach ofmulti-grade protection and distribution automation system for centralized fault allocation andrestoration is proposed.Combined with the prospects of the decentralized access of a large number of DistributedResources in distribution grids, the fault response characteristics of Distributed Resourcesin the case of distribution grids fault is researched. The impact of the Distributed Resources tothe accuracy of directional component is simulated based on PSCAD/EMTDC simulationsoftware. Against the problem of fault direction misjudgment caused by inverter typeDistributed Resources, the improved over-heated region searching method for fault locationof distribution grids is proposed. The principle, workflow and specific implementation plan ofthe method are discussed. Meanwhile the simulation of PSCAD/EMTDC verified theeffectiveness of the improved over-heated region searching method proposed in the paper．To give full play to the advantages of modeled connected distribution network, achieving the purpose of improving the utilization of distribution equipment, it is proposed to adoptmodeled fault restoration method in distribution networks. Through analysis on features oftypical connection modes, the modeled fault restoration strategies and Switching-operationlogic for distribution networks with various typical connections, such as multi-sectioned andmulti-linked grids, multi-in-service and one back-up grids, mutual-backup grids, and4×6grids, are recommended when fault occurs in main power supply line or in power sourcepoint.