A Novel Fault Line Selection Method For Resonant Grounding System Based On Transient Features Clustering

Regulations allow the power system to go on working for 1-2 hours as the line-line voltage is symmetrical when permanent single-phase-to-ground fault occurs in resonant grounding system. However, the fault line must be selected accurately and removed as soon as possible in order to prevent the fault from expanding caused by the raise of the phase voltage and weakness of insulation. On the other hand, line selection has been quite a problem for a long time due to the weakness of fault current along with the influence of many factors such as line structure parameters,nonlinear characteristics of CT or PT, electromagnetic interference, etal. Anyway, there is a big difference existing among spectral characteristics, energy distribution and attenuation characteristic of fault transient zero-sequence currents. Therefore, further research on fault line selection is essential.In recent years, transient-based line selection protection has been a research hotspot since the amplitude of transient current is several times larger than that of steady current.In this paper, transient-based fault line selection methods and research status relevant as well as existential questions that are still not solved in recent years are summarized. A novel fault line selection method was presented based on transient features clustering after analysing the cause of difference between transient zero-sequence currents of fault line and sound lines deeply. In order to solve the fault line selection problem when busbar faults, detection of incoming line’s transient zero-sequence current is introduced. The time-frequency matrix constructed through HHT band-pass filter describes time-frequency features of signals in each frequency band completely and contains the localization information that represents characterization of signals. Then the time-frequency matrix is decomposed by SVD to get singular value quantities which are stable and characterized by robustness and generalization ability so that it can adapt to varies kinds of complicated situations when single-phase-to-ground fault occurs in resonant grounding system. Fuzzy c-means cluster is applied to these time-frequency matrix singular values so as to select fault line by dividing fault line and sound lines into two categories without setting threshold. Besides, mathematical theory of Hilbert Huang Transform(HHT), HHT band-pass filter, theory of singular value decomposition(SVD) and fuzzy c-means cluster(FCM) algorithm are introduced in detail in this paper.A simulation model of lOkV resonant grounding system is established in ATP-EMTP along with the specification and performance verification for each module, thereby imitating the status of single-phase-to-ground fault more accurately to obtain relevant datas close to the real failure situations.Mounts of simulations are carried on aim at five typical faults and other fault conditions including arc fault, Gaussian noise interference, different degree of compensation, high resistance grounding fault occurs at the end of line, two points grounding fault, asynchronous sample, short line grounding fault, different line number, etal.The results show that the proposed method is characterized by good adaptability,high accuracy and reliability, which can provide a certain reference value for engineering.