Location Technology Of Single Phase To Ground Fault In Non-solidly Earthed Distribution Network Based On Multi-terminal Synchronous Waveform

The distribution networks in China are non-solidly earthed systems,and single phase to ground(SPG)faults account for more than 80%of total faults.The fault current of the SPG fault is weak,so the system can run for a period of time with power.The new operation regulation of distribution network for SPG fault in non-solidly earthed systems have been changed from "Operating with SPG fault is allowed for 2h" to "Faulty line must be determined and tripped".At present,the operation effect of the faulty line-section location technology for SPG fault on the site does not meet the requirements of the operation regulations.The fault current is not obvious and are easily affected by background noise.The communication conditions at the site do not meet the requirements for waveform transmission,and the impact of large-scale distributed generator(DG)access makes the problem of faulty line-section location unsolved.At present,the popularization and application of the transient recording fault indicator and the synchronous phasor measurement device of the distribution network provide a more comprehensive fault information support for the fault location of the SPG faultOn this basis,this article has conducted in-depth research on the faulty line-section location of the SPG fault in the active distribution network.The specific research content is as follows:(1)The influence of DG on the characteristics of SPG fault.Analyze and summarize the steady-state fault characteristics and transient fault characteristics of the neutral ungrounded systems and resonant grounded systems when a SPG fault occurs.Based on the control strategy of DG,the fault model of DG is obtained,and the fault model of the active distribution network with DG is further obtained.The analysis results show that DG has a greater impact on the characteristics of three-phase current and line-mode current,and the degree of impact is related to the access location and capacity of DG.However,the access of DG does not change the topology of the zero-mode network.The relationship between the characteristics of zero-mode current in the faulty line and healthy lines is consistent with the relationship in the traditional distribution network,and the relationship between the characteristics of zero-mode current in the upstream and downstream of the fault point is also consistent with the relationship in the traditional distribution network.(2)A method for locating faulty line-section based on approximate entropy(ApEn)of frequency characteristics of transient zero-sequence current(TZSC).When a fault occurs on the line,the TZSC on the same side of the fault point is similar,and the complexity of the phase-frequency characteristics and amplitude-frequency characteristics are similar,and the corresponding matrices of ApEn are basically the same;The TZSC on the different side of the fault point is different,the complexity of the phase-frequency characteristics and the amplitude-frequency characteristics are not similar,and the corresponding matrices of ApEn differ greatly.Based on this,a faulty line-section location method based on ApEn of the frequency characteristics of the TZSC is proposed.This method is suitable for neutral ungrounded system and resonant grounded system.It is not affected by faulty location,grounding resistance,initial phase angle of fault voltage,compensation degree of Peterson coil,DG conditions load conditions.It is immune to noise;the threshold is fixed and does not set with the change of the network structure;the data transmission pressure is small,and the current power communication network can meet the requirements and can quickly determine the location of the faulty line-section.(3)A method for locating faulty line-section based on transient energy.When a SPG fault occurs in the line of non-solidly earthed system,the component in the special frequency band(SFB)of the TZSC is in the opposite direction,and its corresponding transient energy is greatly different in the faulty line-section and the healthy line-section.Based on this,the faulty line-section can be determined.There is a significant difference in the transient energy distribution between the bus fault and the line fault,which can be used to distinguish between line fault and bus faults.This chapter clarifies the range of the SFB of TZSC,and proposes a method for SPG fault location in the non-solidly earthed system based on the transient energy of the SFB component of TZSC.The transient energy has good noise immunity and is suitable for the background of strong noise in active distribution network.It can accurately locate under different neutral grounding methods,fault location,grounding resistance,voltage initial phase angle at fault time,compensation degree of Peterson coil,and the influence of DG and load.When a SPG fault occurs,it can accurately identify the substation bus fault and line fault,faulty line-section and healthy line-sections at one time,with high location accuracy and reliability.