Analysis Of Fault Characteristics And Study Of Protection Technology Of Distribution Network With Distributed Generations

As a new type of power generation technology, distributed power generation providesan effective technology for the comprehensive utilization of environmental friendly energy,such as wind, solar, biomass energy, natural gas and hydrogen, through the scatteredbuilding small or micro power generation system. The distributed power general access oflow voltage distribution system, and it will change the traditional single power radiantpower distribution system network structure and lead to the current, voltage characteristicsignificantly changed after fault, so that make the traditional distribution network faultanalysis method, relay protection and automatic reclosing technology difficult to meet thesafety of power grid operation requirements. This paper, based on failure characteristicsanalysis of the distributed power and combining with the development of the intelligentdistribution network, research the distribution network protection and automatic reclosingtechnology that adapt to the distributed power supply scale accessing.The fault characteristic analysis of distributed power is the foundation of the relayprotection research. Taking the doubly-fed wind power generator (DFIG) as the key point,this paper has researched the short circuit current characteristics of DFIG during externalsystem fault. Because of DFIG generally hold on Crowbar protection, and Crowbarprotection action or not have great influence on the short circuit current of DFIG, therefore,the study of the DFIG’s short circuit current characteristics should research from twoaspects respectively. For remote fault (Crowbar protection not action), this paper based onthe stator voltage oriented vector controller as the prototype, analyses the influence ofdoubly-fed excitation controller features on short circuit current. The DFIG stator faultcurrent analytical expression was given, and verified the accuracy of the theoreticalresearch through the simulation.For close fault (Crowbar protection action), according to the Crowbar protectiondevice’s working principle, this paper based onαβcoordinate system to establish DFIGelectromagnetic transient equation, and studied the basic composition and changecharacteristics of DFIG during three phase fault through the theoretical analysis and digitalsimulation. On the basis of the above work, this paper analyzes the adverse effects that thecharacteristics of DFIG short circuit current bring to distribution network relay protection,and puts forward the relevant strategies. In order to improve the distribution network protection system performance to adapt tothe large-scale DG access, according to the demand for the development of intelligentdistribution network, this paper puts forward a main backup protection integrated protectionscheme that bases on a fault element recognition algorithm which based on the regioninformation. The protection scheme obtain the information of the feeder fault detectionthrough the communication mode then identify the fault element, so as to realize themain protection and backup protection function. The feeder protections only need to timecoordination, no complex action value setting. In this paper, through the example analysisresults, show that the algorithm can correctly identify fault element and the protect trip planis reliability, and this protection trip plan also can prevent the distributed power do islandoperation and guarantee safe and stable operation of the distribution network with highpermeability DG access.Based on the proposed protection scheme, this paper analyzed the problem that thedistributed power supply access brings to former-acceleration and after-acceleration. Theresults show that the distributed power access has no effect to after-acceleration reclosingmode, but to former-acceleration reclosing mode, when distributed power downstreamoccurs fault, it can’t realize fault through operation, may cause reclosing failure. accordingto these, this paper puts forward the corresponding improvement measures,which makecorrection matrix of the trip plan appropriate modification to solve this problem. Whichimprove the distributed power’s failure through operation ability and avoid fault point can’tarc and asynchronous reclosing problem that the distributed power supply access bring to.Finally, the paper summarizes the full text, and forward the prospect of the furtherstudy.