Single-phase Broken-line Fault Detection Technology For 10kV Overhead Insulated Line

Faults in the distribution network are the main factor causing power outages for customers.In recent years,with the widespread application of overhead insulated conductors in distribution networks,the occurrence of single-phase grounding faults has been greatly reduced,which also makes broken-line faults a problem that cannot be ignored.At present,Chinese research in the field of distribution network faults is mostly focused on grounding faults and phase short circuit faults,and there is less research on broken-line faults,and the field also lacks specialized broken-line fault detection methods.For this reason,this paper focuses on the research of the distribution network breakage faults.With the 14 th Five-Year Plan for the development of renewable energy,renewable energy sources are connected to the grid in the form of distributed generation on a large scale,making Chinese distribution network gradually develop from a single-phase radial power supply network to a complex network of multiple power supplies.The inverter-interfaced distributed generation,the most widely used among DG,will change the system current after grid connection,which affects the accuracy of traditional fault detection methods.Aiming at the massive access of IIDG,this thesis researches and analyzes the broken-line fault of active distribution network from both theoretical analysis and MATLAB simulation,summarizes the characteristics of the fault,and proposes the detection method of the broken-line fault.The main research of this thesis is as follows:(1)The characteristics of single-phase broken-line faults in traditional distribution networks are analyzed and fault detection methods are proposed.Using symmetrical component method and composite sequence network,the change characteristics of phase and sequence currents after the fault are analyzed.T he change laws of phase and line voltages and neutral offset voltage before and after the fault point are revealed by considering the system to ground capacitance distribution,fault location,load distribution and other factors.A single-phase broken-line fault detection method based on the zero-sequence voltage difference and negative sequence current on both sides of the fault point is proposed,and the correctness of the method is verified by using MATLAB/Simulink.The method reduces the amount of information to be collected,can escape the system unbalance current,and improves the reliability of fault detection.(2)The types of DG and grid-connection methods are introduced,and the structure and control strategy of IIDG are analyzed.Under symmetric conditions,the inverter-type distributed power supply adopts the traditional PQ control strategy.Under asymmetric conditions,IIDG adopts the negative sequence current suppression control strategy,and the double synchronous rotating dq decomposition is used to achieve the purpose of suppressing the negative sequence current output under asymmetric conditions by controlling the negative sequence current reference value.(3)The characteristics of single-phase broken-line fault in active distribution network and the proposed fault detection method are analyzed.The symmetric component method and the superposition theorem are used to obtain the characteristics of the sequence current at the outlet of the fault bus after the fault;the influence of the fault location,the system capacitance parameters to ground,and the output characteristics of the IIDG on the fault characteristics are fully considered,and the degree of neutral point offset and the zero-sequence voltage difference on both sides of the fault point are analyzed.Using the change of bus outlet sequence current before and after the fault,a fault criterion based on the change of positive and negative sequence currents at the bus outlet is proposed,and the feasibility of the method is verified by simulation.The method improves the ability to cope with multi-distributed energy sources.