Numeral Calculations Of Ampacity For Buried Power Cable Based On The Finite Element Method

The power cable is an important way to transmit electricity and it is significant to calculate temperature field and ampacity precisely for practical project.Up to now,the rated ampacity of the power cable is calculated on the basis of IEC standard.In view of numerous laying ways and complicated factors influencing the ampacity,it may lead to a big error to calculate ampacity only refer to IEC standard.In addition,IEC standard can not calculate the transient temperature of the power cable.Based on the finite element method,this paper analyzes the relationship between steady capacity of the power cable and its influencing factors,and studies the temperature rise response of the power cable under emergency load to realize the reasonable use of the current power cable.Firstly,the basic principle of calculating the temperature field of power cable is introduced which is based on the finite element method.The equation controlling the temperature field,the cable heat sources and the boundary conditions are given combing with characteristics of the heat transfer of the power cable.The calculation process of the cable temperature field is deduced,and the steady state and transient temperature field are obtained.Secondly,the test platform of single 66 kV power cable containing fiber laying in the air is set up.Under the condition of constant load and variable load,the temperature rise test of power cable is carried out to verify the correctness of temperature field based on the finite element method and the reliability of the distributed optical fiber temperature measurement system.Finally,the temperature field model of single and double circuit underground cables is established.The relationship between the coefficient of soil thermal resistance,the coefficient of backfill,the number of cables,the cross-sectional area of the cable,the temperature measurement of the optical fiber and the factor of the periodic load are analyzed,and some useful suggestions for the operation and installation of the cable are given.For single-circuit capacity increase,permitted time of capacity increase is calculated and emergency load-permitted time of capacity increase curve is drawn,which can give a reference for power cable operation.There are two kinds of schemes to choose for double-circuit capacity increase.The capacity increase time of two schemes are calculated and contrasted.The results show that double-circuit simultaneous capacity increase scheme can provide longer capacity increase time.