| The distributed generation technology based on renewable energy sources have attracted widespread attention and developed quickly in order to meet the various needs of energy development, environment protection and the improvement of energy development, environment protection and the improvement of power grid construction in recent years. Distributed Generation(DG) generally connects to low-voltage distribution network, traditional distribution network is generally a radial network with a single power source, and its relay protection is designed and set according to the radial network. Grid connected DG changes the structure of distribution nerwork, which makes the distribution system change from single supply radial network to double source or multi-source network. The power flow is no longer one way flowing from substation to the load. And the traditional protection system, including the setting value, protection algorithm, protection between cooperation, as well as the cooperate relationship between the protection and the reclosing is likely to be affected. Considering the impact of DG on the distribution network, traditional relay protection can no longer meet the requirement of safe operation of the power grid. Therefore, it’s necessary to analyze the impact on traditional distribution network of DG and study on improving protection system to adapt new distribution network with grid-connected DGThis paper firstly introduced some main types of distributed generation and its development status and control mode. The output characteristics of several common types of DG when fault occurs in power grid is analyzed in theory, and the simulation models is built in the PSCAD/EMTDC simulation software platform so that a foundation is established to study the effect of DG access to the traditional distribution network protection.The principle and setting methed of the traditional three-step overcurrent protection method is discussesed. The impact of DG access to the traditional three-step protection is analyzed in detail and verified by simulation. A new protection scheme is proposed by using directional pilot protection and overcurrent protection to solve the problem the distribution network protection with DGA "recloser-fuse" protection scheme based on inverse-time overcurrent relay for distribution network is introduced in this paper. This menthed divided the power grid into several protection areas by recloser, the recloser and fuses coordinate with each other inside the area and reclosers coordinate with each other between the areas. Discussed the adverse effect may produced by distributed generations when they access to the distribution system. A specific protection method is presented which is resetting the protection parameters by analyze the distribution network to meet the requirements of protection coordination, and a simple and effective reclose logic based on one-way communication is proposed to cooperate with this "recloser-fuse" protection scheme so that the reclosing issue can be solved. Simulation results verified the validity of the protection scheme.Finally,a fault locating and fault fast isolation scheme based on the current high frequency transient information is proposed.Using phase-mode transformation and S-tansform to extract the fault characteristic information, achieved the identification of the fault direction by using the high frequency transient current information. A fault section location and isolation strategy is proposed based on this identification method. It has been verified by analysis that this scheme can effectively realize the fault isolation in distribution network with Distributed Generation under the condition of only using current information.It is not affected by penetration or output status of the Distributed Generation which has a good reliability and practicability. |
PDF Full Text Request