Study On Sufficient Protection For Active Distribution Network Based On Fault Characteristics Of Distributed Generators

With the rapid development of new energy resources,a large number of distributed generators(DG)are connected to the distribution network,and "three-stage" current protection is difficult to apply to the network of multiple power.Compared with the passive solution of the traditional distribution network problem,one of the targets of the active distribution network is to deal with the problems in the distribution network actively.At present,there are some problems in active distribution network,such as lack of equipment,difficult access to fault information and simple communication condition,besides,distributed generators have many kinds of problems,such as the variety of DGs,the diversity of control schemes and the change of access position.Faced with the protection problem after the access of DGs,the current protection scheme still adopts the strategy of isolating all DGs when fault occurs,which greatly limits the development of new energy.Therefore,this paper introduces the protection principle of "sufficient criterion",and studies the "sufficient criterion" protection scheme under the "sufficient criterion" principle frame,which can effectively solve the protection problem in active distribution network.The "sufficient criterion" protection thought which breaks the strict requirements of traditional protective relaying,enable protection to take advantage of fault information on the network more fully.The "sufficient criterion" protection is based on the fault characteristics rather than the fault type itself,focusing on those fault features that are most valuable in the set of fault features,making the judgment of common fault features absolutely selective.The "sufficient criterion" protection is different from the traditional protection,and its fault criterion and fault are not necessarily related.As a protection system,the appropriate "sufficient criterion" DG automatic isolation technology is included in the "sufficient criterion" protection scheme to achieve broad coverage and hierarchical protection.Then,based on the difference between the short-circuit currents provided by the DGs and the system when the fault occurs,the criterion of the total current amplitude ratio is deduced.Facing the problem of weak synchronous and weak communication in distribution network,the "sufficient criterion" current amplitude ratio criterion in this paper only uses the information of current amplitude,which eliminates the strict synchronization of data on both sides of the line,greatly reduces the communication cost and accords with the actual situation of active distribution network.Finally,in order to improve the fault recognition ability of the protection,based on the study before,the amplitude ratio of the fault component of the positive sequence current and the amplitude ratio of the negative sequence current are introduced,and the combination optimization between the three is proposed,which achieves the complementary advantages,and can adaptively select the most sensitive sub-criterion in the face of different faults.Considering the advantages of the pilot protection,it is choosen as the basic protection strategy,the polar coordinate representation of the protection action characteristics is also introduced..By cooperating with DG automatic isolation technology,the blind spot of "sufficient criterion" criterion in theory can be covered,and this paper constructs a integrated "sufficient criterion" protection scheme of active distribution network based on DG fault characteristics.A 10 kV active distribution network model is built on the Matlab/Simulink platform,and the effectiveness of the proposed scheme is validated by simulation.