Study Of Small Current Grounding Fault Line

Small current grounded systems are widely used in China, and the single-phase to earth faults are the most probable faults in distribution systems. It is necessary to select the fault circuit quickly for the correct running of system. But because the fault current is too little and many others rensons, this question hasn' t been overcame in the world, this thesis presents a new adaptive method by using the decaying DC component and the method that using the summation of all curcuits' reactive power but one is exclusive subtracts the one which is exclusive.Firstly, this thesis analyzed the fault transient course of small current grounded systems, especially when those systems with arc suppression coil. On the based of these theory, this thesis studyed and analysised the existing curcuit selecting methods. In order to bring precision of fault circuit selection into effect, this thesis point out that each fault circuit selection all has shortcomings. So we should introject the advantages of each method to optimize the fault circuit selection.Secondly, many circuit selection methods can' t be used effective mostly for the fault time doesn' t been located exactly. Using a recursive algorithm of DFT, this thesis can locate fault time exactly, thus solved a tickler which had existed many years .Thirdly, this thesis divided the system when the faulty voltage passes zero from those systems when the faulty voltage is maximal. For the system when faulty voltage passes zero, this thesis presents a new adaptive method by using the decaying DC component. As for the systems when the faulty voltage is maximal, we use the reactive power method for fault line select. Theory study and Lots of digital simulation results show that the proposed method is effective and reliable.Lastly, this thesis discussed the infuences of arcing grounded and disturbance, form the digital simulations, we can say that the method can be used in the arcing grounded system , and this method also can resistfairly disturbance, meanwhile, the method has a low requirement to sampling frequency but has a effective circuit selection.