A New Method About Fault Selection Line And Location For Resonant Grounding System

The happened frequency of single-phase grounding fault is the highest fault in the power system,such failure will make the current increases in system.It is able to generate arc over-voltage when the connection mode of the neutral point is the isolated mode,so the insulation of system will be receive damage.Therefore,it can make the single phase ground fault turn into multi-phase,multi-point failures,so this leads to expand distribution network fault area.In order to guarantee the reliability of power supply,the arc suppression coil connection mode is now mostly used,but the manner of fault feature is not obvious,so it is necessary to put forward a new criterion so that the fault selection line and location is quickly completed.In the paper,the main five works are as follows:1)Discusses the existing fault selection line and location method about distribution network,and introduces its advantages and disadvantages;2)In order to lay a firm foundation for the following principles,the characteristics of single-phase earth fault in the small current grounding system is analyzed;3)The features of sudden variable of three phase current in the resonant grounding system are analyzed,according to the difference of of sudden variable of three phase current between the fault line and the non-fault line,this paper proposes a new method about fault selection line based on sudden variable for resonant grounding system,then the maximum energy ratios of phase to phase are calculated to selecte fault line,which the line corresponding to the largest maximum energy ratio of phase to phase is fault,and maximum energy ratio of phase to phase for the non fault line is closed to 1;4)Analyses the dc component characteristics of fault line and the non-fault line,according to the obvious differences in contents of dc component between fault line and fault line,and S transform has strong time-frequency analysis,therefore,a new method about fault line selection for resonant grounding system based on S transform dc component is proposed,which the dc component of energy ratio about fault line is big,so the method based on the principle can select fault line;5)According to the difference between the sudden variables of the three phase currents of fault upstream and downstream,this paper proposes a new method about fault location based on sudden variable for resonant grounding system,and elaborates the protection criterion and the specific processes about fault location.in order to verify the adaptability of this method,this chapter has carried on the simulation analysis.Considering these factors as the low resistance,high resistance,small switching angle,large angle of closing,the fault pure line fault and the fault mixed line.The result of simulation shows that the new method about the fault selection line based on sudden variable is proposed in this article can well identify the line of many kinds of single-phase grounding fault,and the criterion has higher margin,high resistance grounding fault can also be identified,therefore it can be well applied to select fault line for resonant grounded system distribution network that the structure is more complex.For the method of fault line selection based on the S transform dc component,the simulation results show that the method can well identify the fault line when the single-phase grounding fault occurred in the small angle,especially when the cable is broken.For the new method about the fault selection line is proposed in this article,the simulation results show that this method compared with the zero sequence current energy localization method has higher margin,andcan be applied for the hybrid fault section location,so this method has strong applicability.