Analysis And Protection Research Of Single-Phase Disconnection Fault For Distribution Network With Inverter Interfaced Distributed Generations

The distribution network plays the role of distributing electric energy in the power system,and its power supply reliability and power supply quality are very important.In recent years,with the gradual increase in the application of insulated wires in the distribution network,the probability of disconnection faults has increased.Since there is no obvious overcurrent after the fault,which makes the fault detection and positioning more difficult;Secondly,the access of inverter interfaced distributed generation(IIDG)will affect the single-phase disconnection fault characteristics,the traditional fault protection method is no longer applicable.Therefore,through the research on the control strategy,model and output characteristics of IIDGs,this thesis deeply analyzes the effect of IIDG access location and capacity on the zero-sequence voltage of single-phase disconnection faults in traditional distribution networks,and a single-phase disconnection fault protection method based on sequence component and an auxiliary fault location criterion based on zero-sequence voltage difference are proposed.Firstly,the IIDG control strategy,output characteristics and equivalent model are studied.The IIDG PQ control strategy under normal operation and symmetrical faults in the distribution network is deeply studied,and the IIDG outp ut characteristics and equivalent model under this control strategy are analyzed.The IIDG positive-sequence component control strategy under asymmetric faults in the distribution network is studied,the control model under the double dq synchronous rotating coordinate system is established to realize decoupling of the positive and negative sequence components,and then the positive-sequence component control strategy is used to eliminate negative sequence components.At the same time,according to the magnitude of the positive sequence voltage of the IIDG grid connection point,a low voltage ride-through control strategy is adopted.Simulations are used to verify the correctness of output characteristics and models under different control strategies.Secondly,the zero-sequence voltage distribution of the single-phase disconnection fault of IIDGs connected to the distribution network is analyzed.Aiming at the influence of IIDGs on traditional single-phase disconnection fault characteristics,a fault model of distribution network with IIDGs is established,and the expressions of the zero-sequence voltage on both sides of the fracture under three types of faults: single-phase disconnection and ungrounded fault 、 single-phase disconnection and power side grounding fault、single-phase disconnection and load side grounding fault are derived.By drawing a phasor diagram,the influence of IIDG access location,capacity,fault grounding resistance and fault location on the system side zero-sequence voltage distribution is analyzed.The rationality of the analysis method and the correctness of the analysis results are verified by simulations.Finally,an overall protection scheme for single-phase disconnection based on sequence component is proposed.On the basis of analyzing the nega tive-sequence impedance of each node and the zero-sequence voltage difference on both sides of the fracture after the fault,drawing on the idea of current differential protection,the negative-sequence differential impedance is defined,a protection cri terion based on negative sequence differential impedance is proposed.This criterion uses the negative sequence differential impedance amplitude as the action quantity,and uses its phase to construct an adaptive braking threshold.Aiming at the problem of overload protection failure,the zero-sequence voltage difference is proposed as an auxiliary criterion.The influence of unmeasurable load branch on the above protection criterions is analyzed,and a method for fault location by comparing the negative sequence current amplitude is proposed.The simulation results show that the method can be positioned reliably and is not affected by the neutral point operation mode,IIDG,transition resistance and load.