| With the development of cities and the construction of urbanization,power cables have played a significant role in the construction of power grids.Compared with overhead lines,cables are installed in hidden places such as cable trenches,which are less damaged by external forces,having a lower operating failure rate,and are not affected by harsh weather conditions such as lightning strikes.Although the cable is not easy to be damaged,it is difficult to find and locate after a fault,and it is easy to burn the outer insulation and surrounding wiring,causing a greater power outage.Therefore,online monitoring of the cable status and timely discovery of hidden troubles are of great significance to the safe and reliable operation of cables and the systemThis article focuses on the cable condition monitoring technology,after a comprehensive analysis of the advantages and disadvantages of the existing solutions,select the more significant waveform when the cable has incipient faults to reflect the cable’s insulation status.Different from the existing method of detecting the incipient faults disturbance from the load current,this paper directly detects the disturbance current caused by the incipient faults of the cable from the grounding point of the shielding layer,and specifically completes the following work:First established the incipient faults model.Studied the structure of single-core and three-core cable,analyzed the grounding method of the shielding layer,researched the causes of the incipient faults.On this basis,the cable core,shielding layer and the incipient faults resistance model are established;then the influencing factors that affect the nonlinearity of the incipient faults resistance are analyzed,an index characterizing the degree of linearization of the incipient faults resistance is established,and the arc parameters suitable for the linear model and the nonlinear model scenario are determined;finally,three incipient faults models of the shielding layer grounding cable were established in ATP-EMTP,which verified the feasibility of monitoring the incipient faults from the shielding layer.According to the technology of detecting the incipient faults from the shielding layer current,the typical characteristics of the disturbance current waveform of the shielding layer of the cable incipient faults are established.First of all,based on the linear scene of the model,three incipient faults models of the shielding layer grounding cable are established,the transient expression of the shielding layer disturbance current waveform during the incipient faults is deduced,and the typical characteristics of time domain and frequency domain disturbances for disturbance identification are established;then,based on the nonlinear scenario of the model,the existing feature selection method is improved,and the typical characteristics of disturbance in the wavelet domain are established;finally,the characteristics of the shield current disturbance caused by other disturbance sources in the system are compared and analyzed,and the incipient faults identification feature vector is established.In order to accurately identify the incipient faults of the cable,this paper studied the improved MSVM.First,introduced the principles of SVM and MSVM.Then,selection of the kernel function weights of the MSVM for trace optimization of the sample full divergence matrix is introduced,and an improved MSVM is constructed.Then,a cable incipient faults identification procedure based on the improved MSVM is established,and a simulation example of cable incipient faults is built to verify the effectiveness of the cable incipient faults identification algorithm based on the improved MSVM.This paper analyzed the shielding layer waveform data to monitor the cable insulation state,and established the typical characteristics of the time domain,frequency domain,and wavelet domain of the disturbance current waveform generated at the grounding point of the shielding layer at the incipient faults of the cable for identification,and provides for the subsequent evaluation of the cable insulation state.support,which is active for cable reliable operation. |
