Fault Localization In DG Included Distribution Network And Grounding Method Analysis In Microgrid

With the problem of increasingly prominent global energy issues, the use of clean, low loss, and renewable energy is becoming what people pursue. Distributed Generation, such as photovoltaic, wind generator and battery which has been widely concerned in recent years, it is accessed to power distribution network for user’s power supply. However, the access of distributed Generation has changed the structure of distribution network, and the distribution network fault location method is no longer applicable. Study of new suitable fault location method for Distributed Generation (DG) has far-reaching significance for the reliability of improving the user of power supply and the widely use of DG. Furthermore, in order to take full advantages of DG and reduce its side effects on the distribution network, some scholars put forward the concept of Micro-Grid. At present most studies focus on the operation and control of Micro-Grid, but pay little attention to the grounding method and safety research of Micro-Grid.In this paper, the research content is as follows:(1)This paper describes the existing distribution network fault location algorithm, it analyzes the affection caused by the connection of MG in distribution network, the node type of the distribution network has changed as the MG connects. This paper analyzes the node type of the distribution network with DG, and it proposes practical criterion, and it verifies the effectiveness of the criterion through simulation.(2) It introduces the existing matrix algorithm which generally applied in distribution network, and proposes a new fault location method for distribution network containing DGs which bases on improved matrix algorithm. This method connects the fault information which has been collected from the Feeder Terminal Unit (FTU) with the SCADA system of the distribution network, it isolates the fault location using fault location algorithm. This method does not need matrix multiplies with each other and the location method is simple and observable. It suits to the case where the bus is abnormal.(3) Since there is no TV in real distribution network, a fault location method focusing on distribution network which contains DG is proposed,it exchanges information with intelligent electronic devices (IED) and locate fault via interrelated region state function F(A) and section state function G(i,j) the calculation method of F(A) and G(i,j), static division of IDE interrelated region and dynamic correction is further illustrated. this method do not need the voltage, and thus fits the fault localization of DG included distribution network.(4) Using the action information of current protection section Ⅱ to locate the fault occurred in the upstream region of the DG, and using the action information of current protection section Ⅲ to locate the fault occurred in the downstream region of it, and then remove the fault quickly. This program has the advantage of locating the fault without using the information of voltage and changing the original setting value of current protection section Ⅱ and Ⅲ in distribution network, reducing the workload setting.(5) The model of DG and battery are introduced, and a small scale microgrid is set up. TT system is the best grounding mode in microgrid, since the microgrid can operate safely even if there is not a neutral grounding in DG. During island mode, DG can not afford enough fault current because it is restricted by power electronic switches. Battery is then used to supply a larger fault current. Grounding mat of transformer in microgrid is designed to simulate under fault condition, the proposed grounding mat is proved to meet the safety requirements, since the contact voltage and step voltage inside and outside transformer are both within the safety threshold.