| The smart grid consists of two parts:the smart transmission grid and the smart distribution grid (SDG) and its construction has been a national strategy in recent years. One of the characteristics of SDG is to support a scale of access of the dispersed generators, which are installed and operated in distribution network. The IEEE1547-2003standard encourages the supplier and the user as much as possible to continue to supply power in the condition of islands; some of the distributed generators are allowable to keep on running to supply power to important loads continually when accidents occur. Therefore, the power supply mode of smart distribution will be changed from a single-large-injection point to multi-source mode with distributed power generation equipment throughout the system which causes the change of the power flow, voltage and other aspects. Then the change has great influence on the action behavior and performance of protection equipments, resulting in the low sensitivity, tripping failure, malfunction, and so on. Based on the information of each end of the element, longitudinal protection has simple principle and good selectivity to distinguish the fault internal and external area with reliably, so it has been widely used in the transmission system. Considering the characteristics of SDG, the longitudinal protection can also be applied to the distribution system. Therefore, it is necessary to carry out related research on the regional longitudinal protection system for SDG, analyze relay protection functional requirements of SDG, and present the corresponding algorithm based on the analysis of relay function requirements of SDG. It is also of great significance for the development of SDG.Based on previous research and the characteristics of SDG, a distributed area longitudinal comparison protection scheme is presented, which consists of a management host, the smart distribution terminal unit (SDTU) distributing in the SDG and ethernet passive optical network(EPON). The management host monitors the state of each SDTU and the distribution network topology changes via communication system, and divides the protection areas online to improve the flexibility and adaptation of protection system for the topology changes. As a protection unit, SDTU is divided into various associated domain according to adjacent relationship with the protected areas. The SDTU shares the fault information with the others in the same association domain through EPON to complete the fault detection, localization and isolation by the fault decision algorithm. The whole system formes the mode that the distributed SDTU isolates fault rapidly and the management host completes the online division of protected areas depending on the network topology.Therefore, the division principle of the protected area, the online division of the associated domain and its correction method when the distribution network topology changes, and regional longitudinal fault detection algorithm are the key technology for distributed regional longitudinal protection system, which are also the main research contents of this paper.The SDTU is not only the main execution equipment of the distributed area longitudinal protection system, but also the core equipment of the advance distribution automation of SDG. Real-time peer-to-peer data exchange is very critical for the area longitudinal protection system to detect and isolate fault rapidly. According to the characteristics of SDG, this paper describes the functions of SDTU, presents a general structure design with layered characteristics and then builds its standardized model of IEC61850. Models of area longitudinal protection and islanding detection are described at length, newly added logical nodes are also dealt with in detail. Finally the whole function mode of SDTU is given and described by substation configuration language for laying the foundation of designing the standardized model of SDTU.This paper proposes a EPON communication strategy and its multicast technology after analyzing the communication development status and requirement of the SDG, to ensure the reliable communication among the management host and and SDTUs. The networking scehmes for different distribution network topology are also gave to promote the implementation of the system communication. |
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