Study Of Single-phase Ground Fault Location And Selection Of Distribution Line

The distribution line is usually used in the mode of non-direct grounding of the neutral point,and when the single phase ground fault occurs,because the line voltage still holds the three-phase symmetry,the system can run 1-2 hours,which is of great significance to the reliability of the power supply.Under the current operating conditions,the "instant break method" is mainly used to find the fault line,which causes the reliability of the power supply to decrease.Therefore,this paper studied the fault line selection and location method of distribution line.".Firstly,the steady-state characteristics and transient characteristics of the single-phase grounding of distribution line were studied,and the steady-state characteristics indicated that the neutral point voltage would change and zero sequence voltage will appear in the whole system after single-phase ground fault with the arc suppression coil or not.The zero sequence current in the non-faulted line was equal to grounding capacity current with the direction from bus bar to lines and the zero sequence current in the faulty line was equal to the sum of grounding capacity current in the non-faulted line with the direction from line to bur bar;The transient characteristics indicated that the fault line transient zero sequence voltage and transient zero sequence current polarity were opposite,the non-faulted line transient zero sequence voltage and transient zero sequence current polarity were the same.Secondly,for neutral non-grounded method,this paper proposed group amplitude and phase comparison method to select the fault line.The basic principle of the method was to make a comparison of the stable state zero sequence voltage and the zero sequence current of the multiple lines after the single phase ground,and the purpose of the fault selection line was achieved.And this method included 3Cscheme,2C1 Vscheme and 1C1 V scheme.Then,for the neutral point grounded by arc suppression coil method,this paper pointed out the comprehensive line selection method of high frequency harmonic selection and the transient first half wave principle to select fault line.The basic principle of comprehensive line selection method was that the first half wave selection method was used in the case that the transient first half wave current was larger,and the 7 harmonic method was adopted in the case that the transient first half wave current was smaller.Then,it proposed a fault localization method based on the mutation of feeder automation technique.And the criterion of this method was: the ground range can be positioned as the area between the last zero sequence current mutation switch and the first area without the zero sequence current mutation.In the end,the method of fault selection of two kinds of ground methods were analyzed,for the neutral point non-ground system,group amplitude and phase comparison method were carried out to distinguish fault line,and the results showed that this method can be applied to different operating condition with the ground resistance or not and condition with asymmetrical rectifier load or not.Thus the validity of the method was verified;for the neutral point grounded by arc suppression coil system,the validity of the transient first half wave comprehensive method was proved by the analysis of the first half wave zero sequence current voltage analysis and 7 harmonic analysis.