Research On Fault Type Identification And Location Method Of Overhead-Cable Hybrid Line

With the rapid development of urbanization and more and more cross-sea power transmission projects,the use of hybrid transmission lines is increasing.Fast and accurate determination of fault type and fault point in hybrid line is the basis of stable operation of power grid.But wave impedance between overhead line and cable is different,different wave impedance results in the different reflection and attenuation characteristics of the traveling wave in the transmission process of the hybrid line,therefore,the method of fault identification and localization for a single line cannot be directly applied to the hybrid line.For the fault identification of hybrid line,different from using data at a given moment to identify fault types in single line,but the current data in the period after the failure is analyzed.In this paper,according to the actual operation of the hybrid transmission line,establish five source of fault including single-phase metallicity grounding,single-phase high-resistance grounding,two-phase short,direct lightning stroke(including shielding failure and counterattack)and induction lightning,by changing these five parameters including fault phase,fault distance,grounding resistance,lightning current amplitude and lightning current waveform,get the current data in those cases.Based on the overall analysis of current data in various fault conditions,the four characteristics of oscillation index,harmonic distortion rate,wave similarity mean and energy index are defined,for each characteristic quantity definition threshold is used to classify data to achieve the purpose of fault identification.For the fault location for hybrid line,the common fault location method in the hybrid line is located by the time difference between the two ends of the line,but in practice,the method is more affected by noise and has higher synchronization requirement in measuring device.In order to solve the noise problem in the actual situation,this paper considers the common noise types in the data measurement of hybrid line,for the mathematical morphology calculation only staying in the time domain surface does not cause the time point drift characteristic,use mathematical morphological filter filter the data containing noise,the results show that the mathematical morphology has a good filtering effect on the common noise in the measurement of hybrid line data,and it is not affected by the type of failure.In order to solve the problem of synchronization accuracy of the two devices in the actual situation,the time difference between the measured points at both ends of the traveling wave is only used to determine the fault interval and not using for accurate positioning.After determining the interval,select single-end wave analysis method,the data in this area was performed by morphological gradient transformation.According to the data of gradient transformation,determine the time reaching the measuring point of refracted traveling wave,select the suitable traveling wave and locate the fault point by calculating the time difference and actual velocity.Finally,the method is used to deal with the measured induction lightning data,and the results show that this method has a good effect in the application of fault location of hybrid line.