Scheme Designing And Study On Protection For Distribution Network With DG

In order to alleviate the burden of energy shortage and environmental problems, enhance the compression level of the power grid against major disasters, currently Distributed Generation (DG) integrated to grid has become a new trend of the modern grid. But with increasing distributed generation connected to grid, the operational status and fault levels has changed gradually, traditional distribution network overcurrent protection is no longer fitful. This paper analyzes the impact to grid protection with DG connected, improve the overcurrent protection, design a protection scheme of more flexible configuration and validate it to adapt to the corresponding distributed power assess.Firstly, this article analyzes the impact to current protection with different capacities of DG at different positions in grid. It build a distribution network in the Matlab/Simulink software, connected with a double-fed wind turbine simulation model as distributed power. Operating the simulation and analyze data before and after the access of DG, compare the fault current and mapping it out for visual observation. Analyze the extent of impact to the current protection of reliability, sensitivity, autoreclosure, etc. both theoretically and in reality.Secondly, this article presents two different methods to enable the relay settings improving with the DG capacity level, in order to deal with the distributed power of typical DG(directly connected to grid) and photovoltaic DG(connected to grid through inverter).This improving method make the downstream protection more adaptable to the access of DG and reduce the frequency of mal-operation effectively, it narrow the protection zones and solve the problems of high-sensitivity of protection relay. The article establish appropriate equivalent model of DG, in which the PV model considers a more realistic LVRT control strategy. After that, the article propose improvement programs by limiting the impact to fault characteristics and introducing iterative method to make the protection settings adapt to grid with typical and PV DG connected. Build two types of DG model in the Matlab/Simulink software, compare the simulation results to the calculated data, analyze the performance and adaptive advantages in the improvement.Finally, based on the principle of directional comparison pilot protection and adjacent-lines blocking method, this article design a protection strategy, adapting to distributed power. The direction component based on the change of current phase angle, the selection of the communication channel and the configuration of the autoreclosure are described exhaustively; the time arrangement of main protection and backup protection, the principle of breaker’s action and the integral process of the design are detailed analyzed. With the protection action simulation, we can observe the changes of fault current and logical control signal, test and verify the feasibility of the new protection method both theoretically and realistically.