Research On Single-phase Grounding Fault Line Selection And Location Method In Distribution Network Based On Generalized S-Transform

In order to improve power supply reliability, small current grounding mode hasbeen widely used in medium and low voltage distribution system in China. As cablesare increasingly applied to supply electric power in urban dist ribution system, it willincrease zero sequence capacitive fault current when a single-phase earth fault occurs.What’s worse, single-phase fault can easily extend to two-phase or three-phase shortcircuit fault with long time operation, and the arc grounding fault even lead toover-voltage for overall system. Therefore, detecting the fault line and locating thefault position quickly and accurately has great significance for power supplyreliability, security and stability of grid operation. As fault signal is very weak, faultprocess is complex and field noise disturbs, single-phase earth fault line selection andlocation in distribution network are still not completely resolved.Consequently,single-phase earth fault and its fault line selection&location methods in distributionnetwork have been further studied in the paper.Through taking small current single-phase earth fault as research subject, thepaper deeply analyzed steady-state and transient characteristics of single-phase earthfault, difference of transient zero sequence current signals between fault and non-faultlines have been particularly discussed, all of these lay foundation for the followingresearch.In general, failure transient components are nonlinear and unsteady, easilyaffected by fault condition and difficult to be used to extract fault feature so that theadaptability of fault line selection methods is lower. The paper introduced thetime-frequency analysis technique generalized S-transform（GST）, utilizing it toobtain characteristic information of the transient zero sequence current signals. Thencombining with the relative entropy, we put forward a new measure of energy relativeentropy, it can distinguish the difference between the fault line and non-fault line.Afterwards through calculating and comparing the integrated energy spectrum relativeentropy of each feeder in characteristic frequency band, the fault line can be detected.Finally simulation results show that the proposed method is applicable, it has theadvantages of great margin and strong anti-noise ability.According to the difference of transient zero mode current between ipsilateraland contralateral fault points, a fault location method for single-phase grounding based on generalized S-transform energy spectral similarity is presented in the paper.Firstly, we apply the generalized S-transform to decompose transient zero modecurrent for each monitoring point, thus the time-frequency spectrum matrix can beobtained. Then by refering to the idea of similarity in the digital image processingfield, we put forward a new concept of energy spectrum similarity. Afterwards,through calculating the energy spectrum similarity of transient zero mode currentamong adjacent fault detection points, and comparing it with the threshold in thepre-fault, the fault section can be determined. Finally the simulation analyses andcomparison results show that the proposed location method has great adaptabilityunder the condition of different fault initial angle, different transition resistance anddifferent fault section, and it can always accurately locate the fault section.