Study On Sufficient Wide-Area Protection For Distribution Network With DGs

After distributed generation connected to the grid, the stability and supply reliability of the power system are improved. Distributed generation technology has little pollution, high energy efficiency and good peaking performance. However, DGs’access increases the complexity of the structure. The original single-ended grid network becomes into multi-terminal network, so that the traditional protection method, which loses its selective characteristic, no longer applies. In order to improve DG’s adaptability in the distribution network, a complete self-adaptive network protection solution must be established.The domestic and foreign research status of wide area protection used in distribution network with DGs is summarized, and deficiencies of these schemes are pointed out. On the basis of this, the protection strategy of "sufficient" is put forward to solve the problems brought by the limitation of communication conditions, imperfect measuring equipment and the real-time behavior of the system, in which the distribution network information is extracted and utilized to the maximum extent.In this paper, fault characteristics of distribution network with DGs are analyzed. Based on this, dispersed electrical information is made full use of to realize the wide area protection. Considering the situation that it’s hard to acquire voltage information because distribution network only has a few potential transformers, a new wide area protection scheme is proposed which only uses the current characteristics of nodes as the criterion of fault location under the "sufficient" principle. This scheme uses fault current magnitude characteristic of multi-branch nodes as a criterion for fault search and performs fault search matrix algorithm to determine the zone of the fault. Then, based on the current phase change characteristics of both ends of the line before and after the occurrence of the fault, the line identification matrix algorithm is used to accurately locate the fault location. The principle decreases the network description matrix of order and reduces useless node information storage and operation, which not only reduces the burden of network communication but also has certain adaptability for changes in the structure of the network. A model of distribution network with DGs is simulated axnd a typical example is analyzed to verify the correctness of the protection criterion and the effectiveness of the wide area protection scheme. The conclusion shows that the scheme can quickly and accurately remove the fault in distribution network with DGs.