Studies On Fault Location Method For Ac Transmission Line Based On Double-End Traveling Wave

The problem of the safety and stability cannot be ignored due to the continuous expansion of the grid area and the capacity of the power system,and due to the more complicated operation and management of the power grid.The degree of harm caused by the failure of the power system is often associated with the speed at which the failure is handled.If the failure is not dealt with in a timely manner,the harm may be very serious.Fast and accurate fault diagnosis should be achieved to isolate faulty components and take appropriate action to restore non-faulty area power.Therefore,rapid and accurate fault location is very important for the safe,stable and economic operation of the power system.This paper focuses on the idea of using the attenuation and deformation of the traveling wave head to solve the fault location of transmission lines in order to achieve accurate fault location.Finally,it studies the reliability of stable operation under the influence of various unfavorable factors.The major points of this paper are listed as follows:(1)Analysis of the basic theory of traveling wave and its related characteristics on the transmission lineThe frequency parameters can be gotten through the MATLAB simulation analysis of the actual transmission line system,and the final trend of the modulus parameters can be gotten through the decoupling analysis.The zero-mode traveling wave component is greatly influenced by the zero-mode inductance and the resistance.The zero-mode inductance decreases obviously with the increase of the frequency,while the zero-mode resistance increases obviously with the frequency,which result in that the zero-mode decay constant and the wave velocity increase with the increase of the frequency.The parameters of the aerial modal resistance and inductance are much less affected by the frequency.So the aerial modal decay constant and the wave velocity are far less affected by the influence of the zero-mode parameters.(2)Double-ended traveling wave location method on the transmission lineThe zero-mode traveling wave fault component is generated as the step signal at the fault point,and then the attenuation and deformation characteristics of the process are transmitted along the transmission line to the both ends.The attenuation and deformation of the wave head contains a lot of information,then the results of the fault location can be extracted by the fault feature information on the wave head using the mathematical model.However,it is not easy to measure the amplitude of the different frequency components in the transient signal.The maximum modal value of the wavelet decomposition coefficient at both ends with the specific frequency pointed as the center frequency is extracted to depict the ratio of the amplitude of the double-ended frequency components.Although the ratio of the modulus maxima and the ratio of the amplitude of the double-ended frequency components is a one-to-one relationship,it is not an equal relationship.In this paper,RBF neural network is used to describe this correspondence.Finally,the simulation method is used to verify the proposed method.The feasibility of this method is verified,and the sampling data is short,and the reflection wave head need not be identified in the following wave head.(3)Sensitive analysis of various factors influencing results of the fault locationBased on the transmission characteristics of the traveling wave and the analysis of the earth mode wave head,a waveform identification method based on RBF neural network is proposed.The method is not affected by the transition resistance,neutral point connected,intermittent fault,fault initial angle,the network topology and so on,and has a wide application range.The effectiveness of the proposed method is verified by PSCAD/EMTDC simulation,but the method is only applicable to overhead transmission line,and further research is needed in the application of cable and distribution network.(4)The impact of treble terminal line in location method and improved methodsThis paper introduces the influence of the treble terminal transmission line and puts forward the practical solution.Then,the double-ended traveling wave protection method is proposed according to the principle of waveform discrimination.The following conclusions were obtained:First,the travelling wave is refracted when passes through a branch point.If the parameters are the same in the line,the refractive index is 2/3.That is to say,the amplitude becomes 2/3 of the original after each branch point,while the shape of the wave head has not changed.So the amplitude at both ends of the line will no longer correspond.It is necessary to correct the amplitude of the side that has been attenuated by the branch point.The premise of this method is to make sure that the fault occurs in the specific section,and then the amplitude of this section is accurate,which does not need to be corrected;while the wave amplitude at the corresponding end of the initial traveling wave which has passed through the branch point must be corrected.Second,from the second chapter we can see the wave attenuation and deformation of the travelling wave has a relationship with its frequency,so the travelling wave at the end of the line will have a different shape while the fault happens at different points.Thus,the correspondence between the shape of the head of the wave and the fault distance is described.The mathematical definition,which is the waveform factor to describe the above relationship,is characterized by the attenuation and deformation of the shape of the head,and the size has nothing to do with it.So the branch point has little effect on the accuracy of the results.Do not have to deliberately modify the amplitude of the wave head.And the simulation results verify the reliability of this method.