Research On Fault Location Method For Medium Voltage Distribution Systems

With the rapid development of society, the amount of power supply is becominglarger and larger. At the same time, the requirement for reliable power supply is gettinghigher and higher. It can reduce the time to eliminate the fault by locating the fault pointrapidly and accurately after fault happening, so that the power supply can be restoredrapidly. As the structure of distribution network is always complex, the present faultlocation methods have some limitations when applied in distribution systems. Travelingwave based methods are not sensitive to system operation mode, fault transition resistanceand so on. So much more attention is focused on the research of traveling wave basedmethods for distribution systems. The main work of this paper focuses on further researchof characteristic frequency based fault location method for distribution systems.Choosing the proper signal analysis method is the premise to improve the precisionof characteristic frequency based fault location method. So the common signal analysismethods are summarized at first in this paper. Then the performance of several typicalsignal analysis methods on extracting the characteristic frequency of traveling waves iscompared. The frequency slice wavelet transform (FSWT) is introduced into the area ofpower system signal analysis for the first time, and it proves that the performance ofFSWT is much better. Also the method to choose the optimized regulatory factor (k) basedon energy concentration level for FSWT is presented.A novel method to locate the fault characteristic section based on characteristic timedifference is proposed by analyzing the structure features of typical distribution systems.In this method only the wave heads which reach the substation for the first time need to beanalyzed. And the fault characteristic section can be confirmed by the numbers of thesecond kind of characteristic wave head with dyadic wavelet transform analysis. Thesimulation results verify the validity of the proposed fault characteristic section locationmethod.This paper proposes an improved single-ended fault distance measurement methodbased on multiple measurements to overcome the weakness of the present characteristic frequency based fault location method. At first, the fault characteristic section can beidentified using the data recoded at substation. And then the exact fault location can beconfirmed using the data recorded by one of the terminals of the fault characteristicsection. The simulation and analysis results verify the validity of the improved method.At last, based on the features of distribution systems and the improved fault locationmethod, this paper design a fault location system for distribution systems based on GPRSwireless communication technology. The main research contents are voltage transformerchoosing, data acquisition and transmission, fault location system interface design.