Study On Sufficient Criterion-Based Automatic Isolation Scheme Of DG

Vast insertions of distributed generation (DG) cause the changes of the structures and flo w distribution of distribution network, thus, the traditional relay protection configuration and t he rapid isolation scheme of DG in fault conditions are no longer adapted. Considering the ch aracteristics of lacking protection configuration and information, poor communication conditi ons, big differences of DGs' location and capacity, the auto-isolation scheme for DG based on the principal of sufficient criterion protection is proposed in this paper.The sufficient protection scheme of current amplitude is firstly put forward, after anlysin g the impact on original three-current protection of DG's insertion to distribution network. An d the sufficiency of various faults, different DG's locations and capacity is disscussed, the rela y protection configuration is also optimized. Combining with the above scheme, the isolation scheme of DG is raised to cover the small case where the sufficient current amplitude protecti on scheme can not judging faults. By separating the DG from distribution network, the networ k structure is simplified and the fault detection can be more precise.The isolation scheme for DG based on detecting current amplitude of grid-connection po int is carried out afterwards, considering the present situation of lack of PT in distribution net work. Whether the fault is removed or not can be reflected by the changes of current amplitud e of grid-connection point, which reduces the protecetion cost to a large extent. Furthurmore, i n order to prevent malfunction caused by external factors, which lead to the changes in curren t amplitude of grid-connection point, the db4 wavelet detection is used to detect the current a mplitude mutations of grid-connection point, considering the singularity characteristic of curr ent amplitude under fault conditions. The auto-isolation of DG is realized by the proposed sch erne based on wavelet analysis.In the last part, the simulation model of distribution network with DG is established in th e Matlab/Simulink platform, the proposed shemc of combining sufficient protection and isolat ion of DG, auto-isolation of DG based on wavelet analysis is verified.