Analysis Of Cable Ampacity And Temperature Field In Direct Burial Condition

Power cables have been widely used in the field of transmission and distribution in urban areas because of the unique advantages.Due to the difficulties in laying new cable,it is of great significance to fully tap existing cable transmission potential under the conditions of ensuring safe operation of existing cables,to alleviate the predicament of power shortage in China.Dynamic Thermal Rating(DTR)is limited by the maximum allowable temperature for cable operation.Based on the actual environmental conditions and combined with the thermal inertia characteristics of the cable temperature,the ampacity of the cable can be increased while ensuring cable life.Therefore,accurate evaluation of the conductor temperature is necessary.The importance of DTR technology cannot be ignored.The finite element method can simulate the cable under complex conditions,obtain the temperature field of the cable and capture the temperature change of cable conductor.The accurate evaluation of the cable temperature field using the finite element method will provide valuable information for the power sector to apply the DTR technology,accurately obtain the ampacity of the cable,and ensure the economical and reliable operation of the cable.In addition,the soil around the cable is an important factor affecting the conductor temperature.How to accurately analyze the thermal resistance of the soil is of great significance to obtain the change of the conductor temperature and ensure the safety of the cable operation.First,the ampacity calculation method under the IEC-60287 standard was used to analyze the factors affecting the cable ampacity,classify impact levels and identify key parameters affecting cable current carrying capacity;Transient heat setting theory of the cable is introduced.The temperature variation of the cable conductor under different overload conditions is analyzed through an example,and the significance of the DTR for improving the cable utilization is analyzed through the safe running time and law of the cable under different loads.Secondly,according to the loss calculation method under the IEC standard,the effect of cable axis distance on cable conductor loss and metal sheath loss was analyzed;using COMSOL Multiphysics to establish the finite element model of the cable temperature field,the steady-state temperature field under two grounding methods of the metal jacket when cables are arranged in a plane.The real-time conductor temperature was determined bexample y the combination of analytical method and finite element analysis method.The analysis proved that the use of multi-point monitoring can reduce the error of temperature evaluation to a certain extent,and increase the accuracy of the obtained maximum cable ampacity.Finally,based on the thermal model under the IEC-60287 standard,a cable thermal model for soil layering was established.Ignoring the effect of moisture migration on soil thermal resistance,the optimum depth of the trapezoidal soil model is obtained through actual calculations.Taking the dynamic simulation of cable conductor temperature of finite element analysis as a benchmark,the temperature rise of the conductor obtained under different soil layering models was analyzed,and the optimal trapezoidal soil model considering the calculation speed and accuracy was obtained.In summary,based on the DTR technology,the temperature field of the cable and the temperature change of the cable conductor can be studied in real time to accurately grasp the temperature change of the conductor,obtain a more accurate maximum ampacity of the cable,and effectively increase the current cable utilization rate and ensure the reliability of cable operation.