| In urban power construction,cable tunnel laying is more and more widely used because of its high load capacity,easy management and patrol.At present,there are few studies on Optimization of multi-circuit high voltage cable line laying in tunnels by algorithm.In order to make full use of the load capacity of cables in tunnels,the multi-physical simulation and layout optimization of multi-loop high voltage cables laid in tunnels are studied in this paper.Firstly,the induction voltage and circulating current of metal sheath of cable are studied from the aspect of analytical calculation method.The principle of cross-connected grounding mode and the calculation of related parameters are analyzed.The analytical calculation method of current carrying capacity of cable considering the circulating current of metal sheath is analyzed.Taking the cable lines laid in a tunnel as an example,the mathematical differential equations of electromagnetic field,temperature field and flow field in the tunnel are studied,and the principle of circuit interface is analyzed.Based on COMSOL finite element simulation software,the simulation model of electric-magnetic-thermal-current multi-physical field combined circuit for multi-circuit high voltage cable laid in tunnel is established.By comparing the results of simulation and analysis of sheath circulating current,and comparing the measured and simulated values of actual cable circulating current,the validity of this multi-physical field simulation model for calculating the induced voltage and circulating current of cable sheath is verified.By comparing the measured temperature and wind speed of the actual cable skin in the tunnel with the calculated results of the model,the correctness of the model is verified.Based on the multi-physical field combined with circuit simulation model established in this paper,the circulating current and induced voltage of the cable sheath under different core currents were calculated.The results showed that the circulating current ratio was 7.09% and the induced voltage was 76.58 V.The current carrying capacity of each loop of the 7-loop operation and single-loop operation was calculated and it is similar to the calculated calculation,which further verifies the correctness of the model.Based on the electric-magnetic-thermal-current multi-physical field combined circuit simulation model,given the core current,taking the phase sequence and position of each loop cable as variables,taking the sheath circulation current less than 10% of the core current as constraints,taking the calculation value of the highest core temperature lowest as the objective,by using COMSOL with MATLAB joint simulation to optimize the layout of typical tunnel cable lines in the case combined with genetic algorithm.The optimization results show that the maximum temperature of 110 kV and 220 kV cables decreases by 3.30% and 2.98% respectively after optimization.The simulation calculation of tunnel cables under the optimized layout mode shows that the core current of 110 kV and 220 kV cables increases by 6.75% and 7.14% respectively when the same maximum temperature is reached before optimization.When the core current of 110 kV cables are 400 A and that of 220 kV cables are 700 A,the square sum of circumfluence of metal sheath decreases by 18.09% by the optimized arrangement.. |
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