Study Of Temperature Distribution Characteristics Of Cables Based On Thermal Circuit Model And Fiber Optic Temperature Sensing Principle

During the operation of power cables,abnormal temperature is a precursor of cable failure,and since cables are usually laid underground,real-time monitoring of cable temperature during operation becomes very difficult.At present,distributed fiber optic temperature measurement technology with its long temperature measurement distance,temperature measurement accuracy and other advantages in many areas to make up for the shortcomings of traditional temperature measurement methods.However,after using distributed temperature measurement technology to obtain the cable temperature,it is not yet possible to determine the operating state of the cable,because the temperature distribution characteristics of the cable in different states is not clear,so this thesis takes 10 k V power cable as the research object,using simulation means to study the temperature distribution of the cable in normal operation,insulation aging and insulation failure,and the distribution of the thermal field of the cable in different operating states.This thesis provides theoretical support and data reference for the application of distributed fiber optic temperature measurement technology to the condition sensing of power cables.Firstly,the temperature measurement techniques based on Raman scattering,Rayleigh scattering and Brillouin scattering are elaborated.By comparing the advantages and disadvantages of the three temperature measurement techniques,it is concluded that the distributed fiber optic temperature measurement technique based on Raman scattering is better than the other two techniques in terms of engineering practicality.In addition,the heat transfer mode of the cable and the boundary conditions of heat transfer are explored in detail to provide theoretical support for the following study of the temperature distribution of the cable simulation model.Secondly,the thermal path model of the cable during normal operation was established,and the thermal resistance values were calculated based on the IEC standard method and the shape factor method,respectively,to derive the temporary and steady-state temperature distributions of the cable.A two-dimensional model of the cable was constructed using Comsol simulation software to visualize the temperature distribution of the cable,and the results were compared with those obtained from the thermal path model,and the results indicated that the thermal path model based on the shape factor method was more accurate.In order to verify the accuracy of the thermal path model and the simulation model,a test cable was fabricated and the core and surface temperatures of the test cable during normal operation were measured,and the measured data were compared with the results obtained from the thermal path model and the simulation study to verify the accuracy of the thermal path method and the simulation method.Thirdly,based on the thermal path method and simulation method,the temperature distribution characteristics of cable insulation aging are studied,and the results show that the overall temperature distribution is uniform after the cable insulation aging,but the radial temperature difference will become larger.For the temperature distribution during insulation failure,both axial and radial heat transfer of the cable need to be considered,so a three-dimensional distributed thermal path model is established in this thesis,which can study the temperature rise at the failure point and also derive the temperature distribution curve of the cable axially.A three-dimensional model of the cable is built by simulation software,and the overall temperature distribution during cable failure is studied,and the results obtained are compared with those obtained by the thermal path method to verify the accuracy of the thermal path model.Finally,the device composition and temperature measurement principle of the Raman scattering-based distributed fiber optic temperature measurement system are explained,and the laying method of the fiber optic is explored in detail with the characteristics of cable temperature distribution and the advantages and disadvantages of different laying methods,and the laying scheme of the built-in center type combined with the external laying type is finally determined.In order to demodulate the temperature signal more accurately,a temperature demodulation sensing model is established and the parameters of the model are identified by the sparrow search algorithm.The results show that the model after the parameter identification can achieve more accurate temperature demodulation,which makes the temperature measurement more accurate and can accurately invert the operation status of the cable by combining the characteristics of cable temperature distribution in different states.The thesis has 52 figures,17 tables,and 82 references.