The Research Of Maximum Penetration Capacity Calculation For Distributed Generation Basing On Fault Current Constraints

At present, central power generation, long-distance transmission system and interconnected power system is the main mode of electricity generation, transmission and distribution, and is supplying power for 90% load. This system which has more and more power has its advantage, but there are some disadvantages. With the increasing peak valley load difference, load rate in power system is decreasing every year, and the using rate of generating and transmitting establishments is on a downward trend. Power system larger, the probability of accidents higher .In the large interconnected power system, local accidents always result in a large blackout. So distributed source installing around the user is the substituted mode, enhancing the system of flexibility, security and reliability. So, it is important and significant both in the theory and practice to study DG.With the distributed generation connected into the network, the power flow and short-circuit current in the utility distribution network will be changed. Distribution protection system is designed by way of radial type of a signal source, DG's interconnection makes distribution network into a multi-source network which cause the protection system not to work normally. This paper studies this issue and set about it.In this paper the concept and characteristic of distributed generation is introduced and some concerned technologies in this field are described in brief. With the analysis of its possible influence on the present power system, this paper mainly discusses the effect of distributed generation on the distributed protection. Based on these, an optimization method is proposed for computing the maximum penetration level of DG, taking into account fault current constraints while existing distribution network protection should not be adjusted as much as possible. The fault calculation principle in the distribution network with distributed generation is analyzed. A mathematical methodology converting constraints imposed by fault levels to simple nonlinear inequality constraints is developed. The feasibility of the proposed method is showed by examples of a single distributed generation system and a multiple distributed generation system.