Research On The Identification Of Direct Lightning Overvoltage On 110kV Transmission Line

In eastern China,where lightning activities are frequent,lightning overvoltage is one of the main causes of transmission line faults.Due to the complex geographical conditions in China,the total length of 110k V and above transmission lines in China is 132000 km.The back-flashover caused by induced lightning overvoltage of transmission lines seriously affects the reliability of power supply.It is one of the main causes of transmission line failure and the research focus of stable operation of power system.This paper chooses the lightning protection research of transmission line as the research topic,which has certain theoretical and engineering application significance.In this paper,direct lightning strike is the main research object.According to the different mechanism of direct lightning strike,it can be divided into shielding failure and back flashover.In the calculation,the appropriate lightning current model,tower model,tower grounding resistance,insulator flashover model and arrester model are selected to establish the 110k V transmission line simulation model.By analyzing,simulating and calculating the back flashover and shielding failure of this model,comparing the voltage waveforms obtained,it is analyzed that the polarity of the sudden change of the back-flashover and shielding failure is different,and the positive polarity sudden change occurs during the back flashover,while the negative polarity sudden change occurred in shielding failure.In addition,the duration range of arrester action is also different.Therefore,it was proposed to use the back flashover and shielding failure wavefront polarity to identify the direct lightning overvoltage.Then,according to the theory of wavelet transform,the multi-resolution analysis of the two kinds of overvoltage waveforms is carried out,and the coupling problem between the three-phase overvoltage is solved by phase mode transformation,and the zero-modulus voltage of back flashover and shielding failure is calculated.After that,the quadratic B-spline wavelet and decomposition scale are selected to decompose the zero-modulus voltage signal.By comparing the detail coefficient waveforms of each layer,the modulus maxima of the abrupt change points of the zero-modulus voltage wavefront of back flashover and shielding failure determined,and the appropriate recognition criterion and featuresM₁ and T are extracted.Finally,according to the theory of support vector machine,SVM direct lightning over-voltage classifier is established byM₁ and T.The obtained simulation data are segmented for training and testing,and verified with the 300 recorded data.In the aspect of transmission line lightning protection,the lightning withstand level of two types of direct lightning strike is analyzed,and the lightning point position and lightning current amplitude of the transmission line are comprehensively considered.Under the condition of no protection of the line,installing lightning wires along the line,setting different grounding resistance,installing line arresters and other conventional lightning protection measures,the lightning withstand level of the two types of direct lightning strike is analyzed,the simulation calculation of line back flashover and shielding failure is carried out,which provides a reference for the rational use of lightning protection measures.