An HHT Based Method Of Fault Line Selection And Online Fault Location In Neutral Point Ineffectively Grounded Power System

With the development of economy in China, the distribution network isconstantly evolving. As the price of cable drops down, the outlet lines in distributionsystem are more constituted with overhead lines, cables and hybrid lines. At the sametime, power consumers put forward higher requirements for the reliability and qualityof power supply. Once fault occurs in distribution network, the operating personnelshould find fault location, remove it and restore power supply as soon as possible. Inour country,60kV and below distribution network mostly belongs to the neutral pointineffectively grounded power system. The single phase ground connection faultaccounts for70%～80%failures in the neutral point ineffectively grounded powersystem. Therefore, further study of single phase ground connection fault andidentifying the location of fault rapidly and accurately has an important significanceto improve the reliability and quality of power supply.Firstly, this paper describes the background and significance of the subject,summarizes the domestic and international research trends about the single phaseground connection fault line selection and fault location of the distribution network,and then analyzes the zero sequence current steady-state component andtemporary-state component features after the single phase ground connection faultoccurs in the neutral point ineffectively grounded power system. Secondly, on thebasis of the above research, the singularity detection method is adopted to determinethe polar of each line at fault time, which solves the difficult problem of fault lineselection in the neutral point ineffectively grounded power system. Thirdly, in view ofthe unique advantages of the Hilbert-Huang Transform (HHT) analysis method onanalyzing the complex signals, this paper proposes the Hilbert-Huang Transformanalysis method to detect mutation point of α mode voltage waveforms to acquire themoment when the fault travelling wave reaches the measuring point. Moreover, a single-terminal fault location method is used to realize the position for the aerial wire,cable and cable-aerial wire hybrid line fault. At last, the numerical simulation resultsshow the effectiveness and practicability of this method.