| With the continuous increase of the total mileage of subway in China,the demand for electric energy of subway is increasing day by day,and large-scale transformation and new construction of cable lines are carried out accordingly.Cross linked polyethylene(XLPE)power cable plays a leading role in electric energy transmission and distribution.However,the construction of new cable lines is limited by urban infrastructure,saturation of underground lines,long construction period and other factors,so it is difficult to meet the rising load demand,On the premise of ensuring the safety and reliability of power supply,how to tap the transmission potential of existing power cables as much as possible and improve the utilization rate of cable assets and equipment is a hot issue concerned by power production departments in recent years.At present,the current carrying capacity design of cable is usually calculated based on the standard parameters given in IEC-60287 standard,without considering the complex and changeable operation environment on site,which may affect the power supply reliability of cable on the one hand,and make the current carrying capacity design relatively conservative and fail to give full play to its performance on the other hand.At the same time,the subway needs to start and stop frequently during operation,and the passenger flow also changes frequently,which makes the subway load have strong volatility and randomness.In case of emergency power supply for emergency repair in case of other line faults,there may be transmission bottleneck problems.Therefore,carry out XLPE cable temperature field analysis,consider the complex and changeable operation environment,and accurately determine the cable ampacity and short-term overload power supply capacity,It is of great engineering significance to improve the reliability of subway power supply and transmission capacity.Aiming at the 110 k V XLPE power cable of subway external power supply,this paper deeply understands the internal structure and laying mode of the cable,investigates and analyzes the calculation principle and method of cable temperature field in detail,and carries out in-depth research from three aspects: multi physical field simulation modeling,cable steady-state ampacity calculation method and transient overload capacity evaluation method for cables under different laying modes.Firstly,according to the actual operation of the site,the 110 k V XLPE cable of subway external power supply is dissected,its internal structure and size parameters are obtained,the relevant theories of electromagnetic field,thermal field and fluid field are studied,and the electromagnetic thermal fluid multi physical field coupling finite element simulation model of cable under different laying modes is constructed based on COMSOL software.The cable temperature rise experiment is designed and carried out to verify the reliability and accuracy of the simulation model;Secondly,based on the multi physical field coupling simulation model,the steady-state temperature field analysis and Ampacity calculation of cable under various laying modes are carried out,the influence law of environmental factors on cable ampacity under different laying modes is clarified,and a cable ampacity calculation method considering multiple environmental factors is proposed,which can calculate and adjust the cable ampacity in real time according to the change of environment;Finally,based on the multi physical field coupling simulation model,the simulation analysis of cable transient temperature field under different laying modes is carried out,and the response characteristics of cable transient temperature under sudden load change are explored.Combined with finite element simulation data drive and BP neural network,an application model for cable transient overload capacity evaluation is established,which can evaluate the transient overload capacity of external power cables of subway in real time. |
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