Research Of Influence On Relay Protection Of Distributed Generation Access To Distribution Network

With the problems about energy crisis and environmental protection is becoming more and more serious, it has become a trend that a large number of the Distributed Generation(DG) get access to the distribution network.. When they are connected, the system will transfer from single source type to multiple source type.With DG’s different access types,location and capacity,the distribution’s power flow and fault parameters can be changed, which will affect the operation reliability of relay protection device and the stability of the system. So the work of this paper is as follows:(1)Through the study of wind power generation and photovoltaic power generation, construct the Thevenin equivalent model of these DG.(2)Access DG’s Thevenin model to the network, then according to the characteristics of distribution network,use PQ decomposition to write program to calculate distribution’s power flow.Based on the result,analysis the relationship between distribution’s power flow and DG’s access types,location and capacity.(3)Establish the model of distribution network with the access of DG’s Thevenin model, and the mathematical model of fault current under different access point.Based on the circuit theory, the effect of DG on the structure and relay protection is analyzed.With the establishment of Simulink simulation model,verified the influence of DG’s types, access point,and capacity on protective relaying system. Then problems existed in the existing protection schemes are proposed.(4)Aim at the problems existing in the protection scheme of DG distribution network.Proposed that in the upstream side of the access point all protective devices should be respectively equipped with Power direction component,and the relay protection scheme of this line should be set as the double ended source system’s mode;in the upstream side, adaptive algorithm are used to calculate relay protection setting value.The analysis results shows that the setting value will increase with DG’s accessing positions getting closer or the increase of it’s capacity.The fault types will affect the size of the setting value.