Research On Transmission Line Protection Method On Considering Distribution Network Influence

In the recent years, measuring both of energy and grid, distributed generation has been burgeoning. With the rising permeability of distributed generation in distribution network, distributed generation or micro-grid will have more and more influences on distribution network. The introduction of distributed generation has changed the topology of distribution network, which is from radial network of single supple to multi-supple and multi-lode network. What’s more, this caused the changes on short current size and power flow direction of the distribution network system, even bidirectional flow appears in some line. All of the changes make a big challenge for relay protection system of distribution network. Meanwhile, as the micro-grid is equipped with little short current, bidirectional flow and vulnerable influence by natural conditions, traditional relay protection can’t satisfy the demand of selective with micro-grid further. Therefore, the relay protection of micro-grid has great realistic meaning and profound significance.In this paper, the author takes the little micro-grid which is accessed to distribution network as the research object; gives a deep analysis for the influence on relay protection of distribution network which micro-grid has been accessed to; determines the setting value of transmission line protection method in micro-grid based on voltage disturbances; proposes an atresia strategy used in micro-grid and a communication-based unit-level current protection strategy of distribution network and introduces micro-grid control and protection system. The analysis of the specific content as follows:1) Analyses the influence on relay protection system of distribution network which micro-grid has been accessed to, which includes micro-grid being accessed to different points of distribution network due to the influence on relay protection system of distribution network; the effect on the capacity of distributed generation for the overcurrent protection of distribution network; the accessing of distributed generation influence auto-recloser equipment; the accessing of many distributed generations influence coordination of overcurrent protection of distribution network and other influences.2) After introducing some relay protection systems of micro-grid simply, this paper chooses the protection strategy in micro-grid which is based on voltage disturbances; derives the setting value of voltage disturbances which is used to be the reference of protection; presents some methods of micro-grid islanding detection; proposes an atresia strategy used in micro-grid, and simulates in PSCAD. Finally, the simulation result shows that the protection method in micro-grid based on voltage disturbances process good selectivity.3) Analyses the contradiction between grid and micro-grid of single tip protection in line; proposes a communication-based unit-level current protection strategy of distribution network; introduces many communication modes and unbalanced current in current transformer of protection part and current synchronization measurement in two points of protection part.4) Based on the protection method of micro-grid and unit-level current protection strategy of distribution network, establishes the micro-grid control and protection system, and realizes monitoring and micro-grid islanding detection, adjusts micro-grid control and protection system, communicates with grid, storage of running date, and so on.