Fault Location System For Multi-branch Complex Transmission Line Based On Distributed Detection

As the link between power plants and the end-users,high voltage transmission line is responsible for the important task of power transmission.At the same time,high voltage transmission line is in the most complex environment of power system as well as the most prone to failure.With the development of power grid and the construction of the smart grid,the network structure of power system has become more and more complicated.As the basic unit of complex power network structure,the multi-branch transmission line,including T branch(single branch),2 or 3 branches have become increasingly common.Compared with single line,it is more serious to the power system when the fault occurs in multi-branch transmission line.However,because of the limitation of positioning principle,some traditional fault location methods are not applicable for multi-branch transmission line due to their different structures.Although others can still be used,their accuracy and reliability can not meet the requirements.Therefore,in this thesis,an accurate fault location method for multi-branch transmission line based on distributed detection is proposed,which provides maintenance personnel accurate fault location of multi-branch transmission lines.This can reduce the economic losses and the undesirable social impact caused by power outages.Firstly,this thesis analyzes the travelling wave source of transmission line fault and introduces the wave propagation of travelling wave in the transmission line and its refraction and reflection laws where the impedance is discrete.Then this thesis introduces the phase-mode transformation theory applied in three-phase transmission line and does some research on the travelling wave velocity in wires.The reason why travelling wave velocity is uncertain is also analyzed.In order to remove the effects of wave velocity uncertainty on the result of fault location,it's necessary to monitoring the travelling wave velocity online,which guarantees the fault location precision.On this basis,this thesis proposes an accurate fault location method for multi-branch transmission line based on distributed detection directed against the problems in this area.This method detects the arrival time of first travelling wave front by setting detecting points on transmission line.Each detecting point is composed of three distributed units,which are erected on each phase of the three-phase transmission line.According to the arrival time of the first travelling wave front,the fault branch is confirmed and the online monitoring of travelling wave velocity is realized.In this way,the fault point is precisely located.A simulation test is done by building a PSCAD model and analyzing the data using MATLAB.The test result shows that this method successfully solves the problems of fault location for multi-branch transmission line and has enough precision at the same time.Finally,according to the requirement of the above fault location method,this thesis designs and develops a distributed fault location system,which includes the distributed detecting units erected on lines and background software.The distributed unit is composed of CT power harvesting module,travelling wave detection and data acquisition module based on Rogowski coil,host control module and communication module.The background software is composed of background application and mobile application.The system performance indexes is verified by sensor performance test and high-voltage test and the system is applied on actual transmission lines,which shows that the performance of system meets the requirement of fault location for multi-branch transmission line.