Research On Fault Characteristic And Protection Scheme Of Distribution Network With Distributed Generation

Distributed generation(DG) has a significant effect to alleviate the energy crisis and environmental issues, but it changes the direction of the power flow and short-circuit level, its output randomness and volatility make fault characteristics of distribution network so complicated, which bring great challenges to protect setting and configuration. In this paper, an adaptive directional current protection scheme based on fault component is proposed, based on the research of transient characteristics of DG and its impact to relay protection. Then, a regional protection scheme based on logical information is proposed to ensure protection operation is not influenced by DG. Finally, an online calculation method of the coordination relationships of protections under network dynamic adjustment is proposed, which lay the foundation to set protection parameters and configuration.Since it is difficult for current protection to adapt the DGs accessing, an adaptive directional current protection scheme based on fault component is proposed. First,the fault transient characteristics and equivalent method of different types of DG are studied, and then obtain short-circuit current components and their phase component relationships. On this basis, steady-state fault component is calculated according to fault boundary conditions, then adaptive operating current value and power direction criterion under different types of faults are deduced by using protection’s measuring voltage and measuring current. The operating characteristics of adaptive current protection is not influenced by the types of DG,the outputs of DG and system operations. It can effectively prevent protection refuse to move when voltage drop. Finally, the simulation experiments verify the correctness of the protection scheme.Based on protection incorrect operation influenced by DGs and branches, a regional protection scheme based on logical information is proposed. First, the problems of the local protection with DGs and branches are analysed, and then setting and configuration principles of three-segment directional current protection is proposed.Then the regions are divided based on breaker configuration, and the regional protection operating criterions are deduced by using protection operation information, the protection scheme can locate regional fault accurately, accelerate protection operation, reduce outage time. The criterions have a high fault-tolerant ability by using multi-information. Finally, the examples of IEEE 33 bus distribution system verify the correctness of the protection scheme.It is difficult to calculate the coordination relationships of protections fastly when network is dynamically adjusting, which influence the operation condition of protection.Thus, an online calculation method of the coordination relationships of protections under network dynamic adjustment is proposed. The protection-branch incidence matrix and branch-protection connection matrix are established using adjacency matrix, and then the protection incidence matrix and the coordination relationships of protections are obtained through matrix operation. On this basis, the protection incidence matrix is revised by the protection distance matrix, and then the revise method of the coordination relationships of protections is proposed when the network adjusts. Finally, the typical examples verify the correctness of the calculation method.