Schemes Of Protection For Distribution Networks Including Distributed Generation

Distributed Generation(DG) is an emerging technology, with high efficiency, environmental. However, with the interaction of DG, the traditional single-source radial-network has developed to the complicated multi-source loop-network, bringing traditional protection in a series of problems, such as sensitivity decrease, misoperation and malfunction, etc. Therefore it is necessary to research on the new scheme of protection for the distribution network, which can promote and develop the DG.The paper introduces the characteristics of different kinds of technology 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.In this paper, improvement schemes are proposed in this light of the existing distribution protection, mainly including installing the direction element,modifying the setting value and using the longitudinal differential protection.A new protection principle in distribution network is also proposed: the zone I,II relay of direction and current protection on every line composes a communication unit with the zone I,II relay of the next stage protection on the adjacent 1ine at the upriver last line of DG,finally isolate the fault in the minimum section according to the result of the action of two stages protection. Then based on the analysis upon, a standard analytical model is built. Meanwhile the simulation of PSCAD/EMTDC verified the effectiveness of the scheme proposed in the paper.