Research On Fault Distance Calculation Method Of Distribution Network Based On Single Terminal Impedance Measurement

The distribution network is equivalent to the terminal of the network,which faces the user to distribute the electric energy at the terminal.With the advance of distribution network automation and the development of regional economy,the demand for power supply reliability is getting higher and higher.The transmission characteristics of the distribution network determine that it is vulnerable to the influence of various interferents such as trees in the transmission corridor.The main and branch feeder sections are often not uniform and contain a large number of "T" loads,resulting in the complex and changeable fault characteristics of the distribution system.The occurrence of fault affects the continuity and reliability of power supply.Therefore,the positioning strategy with a certain speed and precision can shorten the maintenance and processing time of the fault,thus greatly reducing the power supply interruption time.At present,there are many researches on the fault distance calculation method of distribution network,but most of the methods have their limitations under certain circumstances.It is necessary to study the common locating method for each fault type.In order to study the fault distance calculation method of distribution network,the circuit models of transmission lines and distribution network under different operation modes are established in this paper.This paper analyzes the transmission wave process of electric quantity under normal operation and fault state.The essence of the change of electric quantity is that the superposed equivalent power supply at fault point sends transient traveling wave components to both sides of the line.The transmission equation reflects the coupling relationship between transmission lines,and the magnitude of the transmission is related to the line parameters and the coupling effect.In addition,the operation mode of the neutral point of distribution network is analyzed and introduced,including the transient steady state electricity quantity research under different modes,the fault quantity always includes the transient steady state two parts,the longer the fault duration,the greater the influence on the power supply and distribution equipment under the operation mode without tripping.Based on the analysis of transmission line model and fault characteristics of distribution network operation,combined with the operation practice of most distribution networks,a calculation method of distribution network fault distance based on single-terminal impedance measurement is proposed.This method takes the single-ended fault electric parameters measurement of transformer substation as the foundation,through the establishment of fault point section of three-phase power flow equations and fault phase volume characteristic equation,Clarke phase mode transformation method is used to decouple three-phase coupling relationship,and introduce the load level to fix to fluctuating load impedance changes,then the selection is obtained by mathematical processing period of fault distance calculation formula.The node electric quantity update formula is used to update the electric quantity of the fault section which does not meet the conditions until the fault calculation distance meets the constraints.The proposed method takes into account different fault types and the effect of transition resistance and only needs to be calculated once in each section.Finally,the accuracy and adaptability of the proposed method are verified by a simulation example of a10 k V distribution network system.