Multi-level Distributed Line Selection System For Single Phase-to-earth Fault In Distribution Network

Non-direct ground neutral system has the characteristicsof reliable power supply,stable opertion,etc,so the power supply mode of non-direct ground neutral system is employed in most of 10kV distribution network.When the single-phase grounding fault occurs,line voltage can balance and the fault line does not need to be broken immediately with load continuous operation,but the danger of dielectric breakdown,two or multi point grounding line,arc overvoltage etc.may be made with long time poeration.In recent years,the line selection algorithm and line selection device have rapid development.However,the device exists false positive or false negative from the reflect of the situation.Fault line even is selected by manual breaking switch in many areas.Improving the reliability of the line selection device thus is extremely urgent.First of all,this paper explians the background and the significance of single phase-to-earth fault line selection,the present situation of the domestic and foreign line selectin and summarise the mian reasons of unsatisfactoty results.Then the paper presents the theoretical basis of the steady-state characteristics and the transient characteristics of single-phase grounding fault in power distribution network,use the software MATLAB to mode and simulate the two kinds of situations in which non-direct ground neutral system and arc-suppression-coil-ground neutral system occur single-phase ground fault for further analysis of the fault characteristics.this paper selects affine moment invariants as the algorthm of fault line selection.Multi-level distributed line selection system for single phase-to-earth fault in distribution network is developed,include Integrated zero sequence current transformer,date concentrator and host computer of fault line selection.Integrated zero sequence current transformer is used to sample the zero sequence current,including three parts of the design of zero sequence current transformer(ZCT),signal processing circuit and signal transmission circuit.The principle of ZCT is firstly analyzed,and then use the software ANSOFT to mode and simulate ZCT to design the suited ZCT.Signal processing circuit is divided into signal amplification,signal hardware filter and signal enhancement and other circuits.Signal transmission circuit mainly uses RS485 bus circuit.Finally,the integrated zero sequence current transformer is designed.The data concentrator is for starting fault line conditions,the zero sequence current signal transmission,including sample circuit of the starting signal of the fault,peripheral circuit of PIC18F86J60 integrated Ethernet module function and procedure transplantation of TCP/IP protocol stack.Host computer of fault line selection analyzes fault zero sequence current and selects the fault line,including zero sequence current waveform data storage,display,calculation,line number setting and the line selection system reset.Finally,test of the whole system is based on lOkV dynamic simulation laboratory of distribution network.When three lines occur single-phase grounding fault respectively.The test results show the whole line selection system using multilevel distributed structure achieves a better division of labor,improves the system performance and the execution efficiency,ensures the stability of the system and data processing ability.Each level of the system using the modular design improves the system maintainability and expansibility,So as to improve the stability of the line selection.