| Due to the fact that operation environment of distribution network(DN)lines is complex and the failure rate is high,fast and efficient fault handling technology is helpful to decrease the outage time,reduce the fault impact range,and improve the power supply reliability and operation safety of DN.A large number of research achievements have been made in the field of DN fault processing,but most based on the data collected by the secondary automation device,while there are few research on controlling the active participation and the coordination between the primary and secondary equipment to improve the fault processing performance.This thesis gives full play to the advantages of coordination between primary and secondary systems,and proposes new principles for inter-phase short circuit fault processing,single-phase grounding fault(SPGF)processing and adaptive reclosure of DNs,details are as follows:(1)In order to solve the problem of multi-level relay protecticn coordination,which caused by the high short-circuit current of urban DN and the minor differencc of short-circuit current along the feeder,a nighly selective protection coordination method based on the current limiting coordination is proposed.The adaptive current limiting device is configured in the substation outgoing switch on the feeder to suppress the short-circuit current,and the selective fault removal is achieved by using the time coordination of the overcurrent protection relays under the current limiting condition.And more,the current limiting protection device of substation outgoing switch is designed and the selection of current limiting impedance is analyzed.For feeders with interconnection switches,the functional configuration and setting scheme of feeder switches that can realize automatic isolation of fault zones and restoration of power supply in sound zones are given.The proposed method car ensure the safety of equipment and the quality of power supply,at the same time,realize the highly selective fault removal,automatic isolation and transfer of short circuit fault between phases of urban DN without communication.(2)For improvement the performance of SPGF processing in small current grounding distribution system(SCGDS),a SPGF processing method based on fault phase grounding is proposed for DN.The reliable arc extinction of transient grounding fault is realized by fault phase grounding,and the automatic isolation of permanent grounding fault section and the restoration of power supply in sound zone are realized,which are combined the zero sequence voltage and zero sequence current variation characteristics of fault phase grounding period.The amplitude variation characteristics of zero sequence voltage and zero sequence current in steady state during arc extinguishing operation of fault phase grounding are analyzed theoretically,and the criterion of local SPGF protection for feeder switch is given by fusing multi-stage information.Simulations and tests show that the criterion is not affected by grounding transition resistance,fault location and system capacitance current.For feeders with interconnection switches,the scheme of single-phase grounding processing system configuration based on fault phase grounding and the feeder switch function setting is given.The proposed method effectively solves the coordination of automatic isolation and transfer power supply for transient SPGF and permanent SPGF zones,and can meet the requirements of power supply reliability and operation safety.(3)In order to make up for the deficiency of SPGF processing method in line break fault with Grounding,a method for line break fault detection and section location of feeder is proposed,which uses the steady voltage of the switch in medium voltage of the feeder and the voltage of the low voltage side of distribution transformer.Combined with theoretical derivation and analysis,the voltage characteristics of the upstream and downstream on feeders and the low-voltage side of distribution transformers are discussed.The correctness of the theoretical analysis is verified by simulation.According to the difference of steady-state voltage characteristics between the medium voltage side upstream and downstream of the line broken point and the low voltage side of the distribution transformer,the identification criteria for the line broken fault of the distribution terminal of the medium voltage line and the monitoring terminal of the low voltage side of the distribution transformer arc given,and the location rules and algorithms for the centralized intelligent line broken section based on distribution automation master station are proposed.The proposed method can effectively improve the scene adaptability of line broken fault detection,and eliminate the blind zone problem of line broken fault detection caused by insufficient distribution terminals at medium voltage,and it can achieve synergy effect with SPGF processing technology.(4)In order to solve the problem of adaptive reclosure of feeders,an adaptive reclosure method is proposed by using the local detection of hetero frequency voltage characteristics of feeder switches,which is produced by the injection of hetero frequency detection signals from distributed generations(DGs).The characteristics of hetero frequency phase voltage and sequence component voltage at point of common coupling(PCC)and switches of feeders are analyzed respectively in the case of no fault and different types of faults,and the selection of frequency and voltage amplitude of different frequency detection signals injected by DG is discussed and confirmed.On this basis,the transient and permanent fault identification criteria of feeders based on the characteristics of sequence component amplitude of hetero frequency voltage are constructed.Furthermore,an improved method of local intelligent feeder automation based on adaptive reclosing is presented,which can effectively avoid the impact caused by blind reclosing to permanent faults and improve the performance of local reclosing feeder automation.It is not only applicable to overhead lines,but also to cable lines. |
