| In recent years,the impact of power cables on the safe and stable operation of power systems is increasing.Accurate calculation of cable temperature field and determination of cable transmission capacity have a vital impact on engineering application.The actual cable load and operating environment are very complex.In the process of transportation and laying,the problem of deformation of metal sheath will be encountered,especially the permanent deformation depression of metal sheath caused by external forces,which will have adverse effects on cable operation.In order to accurately and efficiently calculate the transmission capacity of power cables under specific working conditions,this paper combines finite element numerical method,analytical calculation method and cable test to calculate and analyze the transmission capacity of power cables under various operating conditions,which has a very positive significance for the safe and economic operation of power cables.The temperature field model of direct buried cable is established by finite element method,the thermal field equation and the single-valued condition are constructed,and the numerical calculation of the current carrying capacity of the direct buried cable is studied.A 220 kV direct buried single core cable test platform was built to test the temperature field distribution of the cable under constant and variable loads.The correctness of the static and dynamic load carrying capacity calculation model of the cable established by the finite element method was verified by the test.Combined with the finite element numerical calculation method and IEC analytical calculation method,the carrying capacity of power cable under constant load backfill is analyzed and calculated.The application scope of IEC analytical calculation method is analyzed.The error reasons of IEC calculation method under high backfill thermal resistance are analyzed.The IEC formula is further improved and verified by engineering examples.This paper calculates the carrying capacity of periodic load under daily load curve,analyses the influence of peak-valley difference of load curve on its carrying capacity,and puts forward a new analytical method for calculating the carrying capacity of periodic load through a large number of finite element numerical modeling calculations.Compared with the IEC analytical method for periodic load,the calculation is simple and the accuracy of the existing analytical calculation method is improved.The thermal test of the cable is carried out to analyze the thermal expansion law of the main insulation of the cable,and the radial expansion coefficient of the main insulation is obtained.The finite element method is used to calculate and analyze the relationship between the transmission capacity of 220 kV and 66 kV operating cables and the radial expansion of the main insulation layer under constant and variable loads.Combined with the external impact of 66 kV cable in a certain line in Jilin area,the influence of metal sheath deformation on the cable conveying capacity is calculated and analyzed,and reasonable suggestions are put forward for the safe operation of the cable after deformation of the metal sheath.The conclusions obtained are higher for the cable operation department.Reference value. |
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