Study On Fault-Locating Methods Based On Wavelet And Injecting Signal For Single-Phase Fault In The Neutral Indirectly Ground Power System

Isolated neutral or extinguishing coil grounding mode is widely adopted in distributing network of our country, which is called small current grounding system. Single-phase earth fault is the most of all faults in distribution network. When single-phase earth fault occurs in small current system, because fault current is very small and line voltage keeps balanced, the grid system is allowed maintaining running two hours and electric power supply isn't influenced. But, if running time after fault excesses scheduled time very much, the earth insulation of no faulty phase will be destroyed very easily; On condition that the fault isn't deal with in time then it will be likely to induce two-phase earth fault. Consequently it is very important to power supply reliability and equipment or person safety that single-phase earth fault is rightly detected in time and fault-line is segregated from power net very soon by taking adapted measures. It has important theory signification and flesh and blood signification to alleviate work of line inspection worker, to enhance dispatching quality and realize distribution automation that fault can be detected correctly, and fault-spot can be located on the branching line of mains, and the distance between fault-spot and test-spot can be obtained and the test results can be displayed on monitoring screen .Selecting-line equipments at present in distribution network feeder automation system can't distinguish feeder main which single-phase earth fault occurred on well and truly, say nothing of they can distinguish fault branch from all branches and locate the distance between test-spot and fault-spot of branch line.The thesis researches the difficult problem by using my own method.At first, the thesis analyzes the characteristic of small current grounding system and researches the status in quo of fault selecting-line and fault test-distance. Afterwards I put forward my own method. Finally I simulate and research the task by means of MATLAB/SIMULINK.The thesis bringing forward synthetic selecting-line method which are made up of waveform-identifying method based on injection signal from potential transformer tobusbar, and wavelet-analysis method and energy method. Simulation results state that this method can overcome some deficiency of many method and has lots of advantages, such as it has enough endurance in transition impedance—the endurance is as ten times as existent method or so, busbar -fault and line-fault can be distinguish very easy, normal line and line-fault can be distinguish very easy, mistake-selection ratio is very low, and the method have a strong reliability and sensitivity. It can also overcome the deficiency— not adapting fault environments that fault detecting equipments are made up of singleness principle.The thesis also brings forward an new method of on-line locating single-phase grounding fault in distribution network. This method bases on wavelet-analyzing power network traveling-wave signal and on injection signal from potential transformer to busbar. Simulation research states: it can detect electric distance between test-spot and fault-spot and find fault branch line on main from all branches, and this method can avoid earth resistance influence or disturbance. We can adjust amplitude of injection signal according to needs time after time to enhance location fault veracity.It needs to be indicated that the study results above is come from ideal condition, and it is a long distance to apply the method to practice in electric power engineering.But, it can't be negligible that this method has instruction significance to distribution network automation study.