Fault Location Of HVDC Cable Based On Time Frequency Domain Energy Analysis

Compared with overhead line,HVDC cable has the advantages of lower failure rate and less floor area.It is widely used in Voltage Source Converter based High Voltage Direct Current(VSC-HVDC).However,it is difficult to detect the fault point after cable failure because the cable is often laid on the sea floor or buried deep underground.This often results in prolonged power outages.Therefore,it is very important to collect real-time operation data of cable and locate the fault point timely and accurately after the fault occurs.Taking HVDC cable as the research object,this paper presents an accurate fault location method for cable faults based on time-frequency domain energy analysis.The main contents of this paper are as follows:Firstly,it introduces the application scenario of DC cable,part of VSC-HVDC project and the technical advantages of VSC-HVDC.Aiming at the problem that the fault point of DC cable is difficult to be determined timely and accurately,the fault location method of DC line and the related research on fault location of DC line made by scholars at home and abroad are briefly introduced.Secondly,the basic composition of VSC-HVDC system,the basic structure of DC cable,the centralized parameter model and the distributed parameter model of the cable are introduced in detail,and the mechanism characteristics of the two models are analyzed in detail.The main fault causes of DC cable and the generation and propagation mechanism of fault transient traveling wave are described.Then,the principle of S-transform and the time-frequency domain matrix information of S-transform are introduced.The mechanism and characteristics of DC side faults are analyzed in detail according to the VSC-HVDC model,and the calculation formulas of natural frequency and natural main frequency are deduced.DC cable is decoupled,the phase mode decoupling formula is derived,and the concept of S energy spectrum is put forward.On this basis,the fault location system of HVDC cable is constructed,which is composed of two parts.Firstly,the fault location method of single-frequency energy DC cable based on the natural main frequency is used to make the initial judgment of the DC cable fault area and reduce the fault detection area.The second is a fault location method based on the optimization of the Particle Swarm Optimizati(PSO),which is based on the multi-classification Support Vector Machine(SVM)and the energy ratio.By using the decoupling formula and S transform to process the acquired fault signals,the 5 and 6 mode energy of different frequency bands are obtained,and the energy ratio of each frequency band is calculated.The energy ratio is input into the PSO-SVM model as the input sample for learning and training,and the fault points are accurately located in the reduced fault detection area.Finally,PSCAD/EMTDC is used to build a double-ended flexible HVDC transmission model,and the fault location system of HVDC cable is simulated and verified by timefrequency domain feature analysis.The simulation results show that the fault location system proposed in this paper can locate the fault point in time and effectively,and the error is less than 1km.