Research On Fault Location Method Of Medium Voltage Distribution Line Based On Multi-point Information

The distribution network is an important basic engineering facility that not only ensures social and economic development,but also ensures the quality of life of the people.At the same time,the distribution network has the characteristics of complex network structure,numerous branch nodes and poor operating environment,which makes it extremely prone to failure.The consequence of this is a direct blackout,which seriously endangers the safety of people,equipment and systems.The length of the distribution network line accounts for about 90% of the length of the power line,and nearly 75% of the power outages are caused by the distribution network.Therefore,accurate fault location of distribution network is the key technology to reduce blackouts and accelerate power supply recovery.The overwhelming majority of distribution line faults are grounding faults,which have large transition resistance,complex evolution process and strong correlation with neutral grounding mode.This kind of fault usually presents the characteristics of weak signal and intermittent signal.Operational experience shows that traditional fault location methods can not effectively detect and locate faults accurately.This has been a technical problem that has been primarily focused on and urgently be solved at home and abroad.At present,it has been included in the national key R&D program of China as a research project.In recent years,the problem of fault detection and location in distribution networks by using transient variables has attracted widespread attention,and some new methods have been proposed.However,due to the serious shortage of measurement equipment and the lack of advanced measurement devices,the engineering application effect of these methods is not good,nor can they meet the requirements of practical engineering application.With the support of the national key R&D program,wide area measurement devices and systems have gradually been recognized and applied in distribution networks,which provides a solid support for the development of new fault location technology in distribution networks.Distribution network fault location mainly includes fault section location and fault distance detection.Fast fault section location is conducive to isolating faults quickly and restoring power supply rapidly.Accurate fault distance detection is beneficial for speeding up maintenance and shortening blackout time.Both of them are the key technologies of distribution automation system.Based on the measurement information of the wide area synchronous phasor measurement unit of distribution network(D-PMU),the fault location and fault distance detection methods are studied in this paper.Firstly,this paper discusses the location method of grounding fault section of distribution line based on multi-criteria fusion with engineering practice.In multi-branch distribution network,the zero-mode current of ground fault with weak fault characteristics and its detection characteristics will be distorted.In addition,the serious shortage of measuring equipment in engineering practice leads to the blind area of traditional fault location method based on single criterion.In order to solve this problem,this paper combines the similarity and direction of zero-mode current,and proposes an accurate grounding fault location method without blind area,under the condition that the measuring points at the branch of the line satisfy the incomplete arrangement.On the basis of the above,this paper further studies a method for detecting the grounding fault distance of distribution lines based on the time domain information estimation.In order to effectively solve the contradiction between the high sampling rate requirement of accurate estimation of time domain information and the limited actual sampling rate,this paper proposes a method of low frequency time domain signal reconstruction and cubic spline interpolation to pre-process the measured data.Then,it uses Bergeron equation in time domain and voltage and current constraints at fault points to construct the fault current difference criteria.And,only calculating the fault current at the estimated point can accurately detect fault distances.In order to further improve the accuracy of fault distance detection.The fault distance detection method of distribution line based on multi-point traveling wave information is also studied in this paper.This method is aimed at the problems of serious traveling wave dispersion,limited measuring point allocation and difficulty in calculating accurate wave velocity in multi-branch distribution network.This method is aimed at the problems of serious traveling wave dispersion,limited measuring point allocation and difficulty in calculating accurate wave velocity in multi-branch distribution network.Firstly,non-fault region is identified by using traveling wave synchronization time difference,and traveling wave velocity is calculated online.Furthermore,the fault branch recognition matrix is constructed and the fault branches are searched step by step.Finally,the fault distance can be accurately detected by using the network traveling wave time difference and its redundant information.This method has good technical performance in multi-branch distribution network.As long as the measuring points are arranged at the end of each branch,the fault distance can be accurately detected,and the location results are not affected by the wave velocity.With the improvement of D-PMU sampling rate and the development of communication technology,this method will have wide application prospects.This paper establish typical distribution network models,the simulation analysis and verification of fault section location and fault distance detection methods are carried out respectively.The results show that all the methods mentioned above have excellent technical performance and meet the expected technical specifications.