Research On Method Of Selecting Line And Phase For The Single-phase Grounding Fault Of Small Current Grounding Power System

Small current grounded system means the neutrals indirect connected with the ground,which is also called neutral indirectly grounded system.When the single-phase ground fault occur in neutral indirectly grounded system,since the fault current is very low and line voltages between the three-phase remains symmetric,therefore the system can still provide power supply to the load;Nowadays the new rules set the continued work time can be 8 hours.Due to the small current grounded system has reliability advantages in power supply,it has been widely used in power distribution networks including 35 kV and below in China.However,since the voltage in non-fault phase arises ~ 1.732 times when the single-phase ground fault happened.If the system operates under this situation for long time,the fault situation is very easy to deteriorate from single-phase ground fault to twophase or multi-phase ground fault.Therefore,the rapid determination of line fault and phase fault is very crucial.In recent years there are lots of interest in using of transient signal to construct line selection algorithm,lots of information are contained in fault current initial wave components signal,and it is very difficult to extract,thus special analysis methods are needed to process the signal.Traditional real wavelet analysis methods can extract the magnitude information,but it has some disadvantages such as poor directional properties,lack of phase information,and poor sensitivity of translation,etc,which have tremendous affect on line selection results;General complex wavelet analysis can provide phase information,but not analytic;Dual-tree complex wavelet analysis can be used through construct Hilbert transform pair to satisfy approximate analytic condition,meanwhile it also has the advantages of general complex wavelet analysis,thus it is very suitable for transformation analysis of current traveling wave signal.This paper launched the research to this issue through analysis the advantages and disadvantages of line selection and phase selection method,furthermore,new method of line selection and phase selection are explored,by the means of systematically analysis on the characteristics of steady-state components and transient-state initial wave components after single-phase ground fault in low current grounded system,and analysis the difference of characteristics components between fault line and non-fault line.In recent years there are lots of interest in using of transient signal to construct line selection algorithm,lots of information are contained in fault current initial wave components signal,and it is very difficult to extract,thus special analysis methods are needed to process the signal.Traditional real wavelet analysis methods can extract the magnitude information,but it has some disadvantages such as poor directional properties,lack of phase information,and poor sensitivity of translation,etc,which have tremendous affect on line selection results;General complex wavelet analysis can provide phase information,but not analytic;Dual-tree complex wavelet analysis can be used through construct Hilbert transform pair to satisfy approximate analytic condition,meanwhile it also has the advantages of general complex wavelet analysis,thus it is very suitable for transformation analysis of current traveling wave signal.Therefore,based on analyzing different kinds of complex wavelet transform constructing principle and methods,dual-tree complex wavelet analysis is selected as signal process tool to analysis initial current traveling wave signal.In this work,a line selection and phase selection method based on dual-tree complex wavelet analysis is proposed,this method,through using 2-level deposition of dual-tree complex wavelet,is use the difference of amplitude and polarity corresponding to fault/non-fault line and fault/non-fault phase to realize fault-line and fault-phase selection.Due to the using of the initial traveling wave is not effected by the type of grounded neutral point,the length of transmission,distance of the fault location and the fault angle,this method offers a theoretical foundation to achieve accurate and effective line selection and phase selection.By means of simulation of different examples,this line selection and phase selection method is verified that there is no effect of grounded neutral point type,fault angle,distance of the fault location or the length of transmission,which can be used to quickly and accurately determine fault-line and fault-phase.