Theoretical And Experimental Study On Accurate Calculation Of Single-core High-voltage Cable Core Temperature Based On Skin Temperature

Electric cable's transmitting capacity was mainly restricted to its heat insulation level. To ensure the safe operation of the cable, mastering the temperature of the cable ontology was needed. There were many dynamic factors influencing the cable, This paper, in order to analyze various non-ideal factors'change that influence the temperature of the cable, based on single core cable equivalent heat current, using the method of node theoretically get the equation of the temperature of cable conductor and the thermal conductivity of materials in different layers, and by using the sensitivity analysis method, study the influence of each parameters on the cable core temperature. Through theoretical calculation and analysis of experiment data, it was gotten that the cable conductor temperature is inversely proportional to the sensitivity of thermal conductivity coefficient of the cable material. In each layer, the temperature of cable conductor received more influence from the coefficient of thermal conductivity of the air gap. The small changes from the coefficient of thermal conductivity of the air gap layer can lead to the large fluctuations of the conductor temperature value.Based on the sensitivity analysis of heat current model , the influence of the temperature on the conductor was given quantitatively by the parameters change , and theoretical basis was available for the accurate calculation of cable conductor temperature and load flow and the accurate selection of cable thermal parameter value.Based on this, further studies were done on the cable material thermal parameters'nonlinear character and the wire core temperature calculation error without consideration of heat caused by transmission along the line of the spindle. In order to improve the calculation accuracy of the conductor temperature, nonlinear finite element analysis was used with all kind of input parameters. Experimental study was conducted on cable conductor's radial, axial temperature gradient and heat diffusion rule , in order to analysis the effect on axial and radial cable core's temperature distribution caused by operation current factors and the external environment temperature.Considered with heat conduction theory, the effect of cable thermal parameters'change according to temperature on the cable conductor was studied, the model of nonlinear finite element analysis for cable conductor temperature calculation was built, and the model was validated and fixed according to the experimental data. By building middle joint finite element analysis simulation model, the calculations of conductor temperature on the model considered about axial heat conduction and the one considered about radial heat conduction were compared. By comparing the experimental data and the results of the finite element simulation,we included:if we ignore the heat of cable which is along the axial transmission and the changes of thermal parameters which can cause the calculation error of wire core temperature,the nonlinear finite element method can improve the calculation precision of wire core temperature, and provides a reference for improving the real-time calculation accuracy of the cable.The results verifide the effectiveness of the nonlinear finite element method which is used in the real-time calculation of cable conductor temperature, and the effectiveness laid a foundation for the temperature monitoring of cable conductor and load forecasting under high temperature; It also confirmed that,for heat transfer body which is axial obviously,the thermal circuit model which only consider the cable heat transfer cooling along the radial can cause wire core temperature calculation error,so we need to consider the axial heat transfer model to improve accuracy.In this paper, the author adopts the method of combining the thermal circuit model with the numerical analysis.This mothod not only can reduce the amount of computation to speed up the processing speed,but can meet all kinds of irregular cable for temperature field and improve the calculation accuracy.This is to provide a reliable guarantee for the temperature monitoring of cable conductor and the calculation of ampacity.