Research On Protection Configuration And Setting Of Distribution Network With Distributed Resources

The exploration of Distributed Resources (DR) has been part of China’s energy development strategy due to the exhastion of traditonal follsil fules and growing environmental problem, but the increase in DR penetration has also caused some problems for automatic devices and traditonal protection in power grid. The connection of DR transforms the grid topology from single-source radial structure to multi-source structure, changing the original level and direction of fault current, resulting in a decrease in traditional protection sensitivity, even causing maloperation. When the capacity of connected DR is relatively large, traditional current protection may not be able to meet setting requirements.In order to solve these problems, this paper conducted fault simulations based on models of wind turbine with Doubly Fed Induction Generator(DFIG), Directly driven wind turbine with Permanent Magnet Synchronous Generator(D-PMSG), and grid-connected photovoltaic power system in PSCAD and MATLAB/SIMULINK, then the fault current characteristics of theses three DRs and their potential influences on relay protection under symmatrical and unsymmatrical faults are discussed. The simplized calculation of short circuit current for wind turbine generators is proposed, and the influences of DR connection location and capacity difference on distribution network current protection is studied, supported by PSCAD simulation. Also the allowed wind farm capacity without affecting original protection is calculated. The paper proposed a protection scheme which combines current protection with distance protection, and based on this scheme, the protection configuration and setting of a 10kV distribution network is calculated, results proving the validity of the proposed scheme. Another wide-area protection scheme base on overcurrent protection is also proposed, and the simulation results of a 10kV distribution netwrok proved this scheme can adapt to the flexibility of DR operation and react properly in distributed networks with or without DR connection.