Reaserch Of The Protection Of The Distribution Network With Distributed Generator

Since the world wide oil crisis in 1973, the shortage of energy and the environmental contamination have become the worst problems of the globe. To solve these problems, the technology of Distributed Generation (DG) has been paid attention to and has developed dramatically, such as wind power, solar cells, micro-gas turbine and fuel cells. Generally large capacity DG extracts power through transmission grid. Small capacity DG's location is close to the load which is connected to the distribution grid, it is economical and beneficial to the society as the result of the save of investment, decrease of loss, heightening of the power reliability. However because DG connects to the distribution grid, it is possible that the topology of the network has changed and becomes a double sources network. So it is necessary to adjust the scheme of the distribution protection and automatic closing devices which are designed basing on a single source network. Otherwise the fault cannot be cleared exactly in time and it is even harmful to the security and stability of the distribution devices.The paper introduces the characteristics of different kinds of energy sources of DG. Because most small capacity DGs connected to the distribution network use electrical-electronic devices to supply the power, it is necessary to analyze the control scheme and the characteristics of fault respondence of DG to complete the equivalent model of DG. This model will be used for the analysis of the effects of DG on the protection system of the distribution network.The paper processes qualitative analysis of the effects of DG on the feeder protection when the connection point of DG differs. Then based on the analysis upon, a standard analytical model is built. The curves of currents measured by different relays are drawn up with different capacities of DG through the calculation of the theoretical formula. The results are compared with the conventional setting of current protection to analyze the effects of DG on the selectivity, sensitivity, reliability of the traditional protection and automatic closing devices. Meanwhile the paper validates the analyzing results using the simulation of PSCAD/EMTDC. Finally the methods are respectively presented to solve different problems, such as the improvement of protection function and the approach of intentional islanding in the microgrid.