Study On Automatic Isolation Scheme Of DG Under The Condition Of Sufficient Criterion Protection

Vast insertions of distributed generation cause the changes of the structures of distribution network. The traditional relay protection devices aiming at distribution network is no longer adapted, and new sufficient criterion protection is put forward. Sufficient criterion protection is proposed based on the condition of distributed network with DG, which considers the DG features sufficiently. This method doesn’t need the isolation of DG in fault condition, increase the adaptations in grid and ensure the excision of the line faults in any condition. Sufficient criterion judgment can detect the majority of the failure cases and ensure the reliable removal of faults except for some rare cases needing the isolation of DG. Also the cost of the reconstruction is low. In this paper, basing on the sufficient criterion protection, the auto-isolation of DG is researched in detail.In this paper, analyzing the protection configuration according to different inserting position of distributed network with DG, the traditional current protection can be reserved through appropriate improvement. In the areas where the traditional current protection can’t apply, the requirement of DG isolation is analyzed based on sufficient criterion protection. Also the DG auto-isolation method, which set the protection time according to the requirement, is put forward.Used for inverse DG, auto-isolation restart scheme based on voltage drop is proposed, analyzing the effect of distributed network failure to grid-connected voltage and current. The wavelet detection method is proposed, acting as assistant criterion, to distinguish the electrical changes of DG grid-connection point caused by other abnormal factors, increase the detection ability and reduce the restart probability of auto-isolation. Low voltage ride through ability should be considered when setting of DG isolation time, with multi-stage isolation cooperation. The operation scheme of lonely island with DG is also put forward solving the lonely island caused by failure isolation.The coordination control of distributed protection and DG body protection are studied. The method reduces the splitting probability, protect the reliable removal of distributed network and promote the development of distributed generation.Finally, the simulations based on Matlab/Simulink are conducted, which verify the correct response of sufficient protection, and the effectiveness of DG auto-isolation in sufficient protection.