Mathematical Modeling And Operational Characteristics Analysis On A 35kV Three-phase Superconducting Cable

With the development of economy and society,the electricity consumption in large cities is increasing day by day,and the lack of space resources limits the addition of conventional cables in urban centers.Superconducting cable has become one of the solutions for power supply in large cities because of its small size,large transmission power and low electromagnetic pollution.Conventional three-phase independent superconducting cable is large in size and suitable for power transmission lines,it is better to lay superconducting cable in urban distribution network using traditional underground cable channel without redesigning the position for superconducting cable.The three-in-one superconducting cable and the triaxial superconducting cable can meet the above requirements with the advantages of small volume.This thesis mainly focuses on the parameter modeling and operation characteristics of superconducting transmission lines in urban load center,and studies two kinds of superconducting cables with different structures:three-in-one superconducting cable and triaxial superconducting cable.According to the structural characteristics of the two kinds of superconducting cables,based on the branch parameter equivalent method,the equivalent theoretical analysis mathematical model of the three-in-one and triaxial superconducting cable are established respectively,and the variation law between the cable voltage and current is obtained.In order to solve the problem of uneven current distribution in the layer of three-in-one superconducting cable,a conditional screening algorithm is proposed,based on the algorithm,a calculation program is programmed in MATLAB to optimize the three-in-one superconducting cable to realize the current sharing operation of the conducting layer of each phase,and exploring the effect of shield resistance,phase-to-phase distance on shield current;for the three-phase unbalance problem of the triaxial superconducting cable,the conditions for realizing the three-phase balance are analyzed,and a new structure is designed to meet three-phase balance.The AC loss and temperature characteristics of one phase of the three-in-one and triaxial superconducting cable are studied.Bsaed on COMSOL Multiphysics,the superconducting cable is modeled according to the structural characteristics of the superconducting cable and the characteristics of the superconducting material.The AC loss value of the superconducting cable is calculated,and the AC loss value is used as the heat source to simulate the temperature field of the superconducting cable.Finally,the temperature rise of two kinds of superconducting cables in the steady-state operation is obtained.Finally,a 40-cm long three-in-one superconducting cable is hand-wound,and the operation performance of one phase is tested.The experiments of critical current,current-carrying characteristics and AC loss(electrical measurement method)are carried out.The experiment results show that the current sharing effect of inner and outer layers is better,which verifies the effectiveness of the optimization program;the results of AC loss measurement are compared with the simulation results to verify the correctness of the 2D simulation model.