| Due to the disadvantages of overhead transmission lines,such as affecting the beauty of the city and being vulnerable to lightning,typhoon,ice and snow and other natural disasters,power cable lines have become the main power transmission mode in urban distribution network.But in recent years,power cable safety accidents occur frequently,more than 90% of which are caused by intermediate joint failure,which not only affects the safe and stable operation of power grid,but also poses a certain threat to personal safety.In order to prevent the cable from being damaged by external force and prevent the failure of the intermediate joint from spreading to the adjacent cable,the cable intermediate joint needs to be equipped with an explosion-proof box,but it is bound to extend the heat conduction path of the intermediate joint and affect its heat dissipation performance.As the most important performance parameter of explosion-proof box,how to ensure its explosion-proof and heat dissipation performance through structural design plays an extremely important role in reliable protection of intermediate joint and reducing fault range.The main contents of this paper are as following:(1)The basic structure of the distribution network three core cable intermediate joint with explosion-proof box is introduced,and the heat dissipation characteristics of the cable intermediate joint during operation is analyzed.Given the inseparability between the magnetic field and the thermal field,the magnetic thermal coupling model of the three core cable intermediate joint considering the contact resistance is established.(2)Taking the intermediate joint of 20 k V three core cable in Sino-Singapore Guangzhou Knowledge City as an example,the temperature rise of the joint with explosion-proof box under 289 A current is calculated,and the accuracy of simulation calculation is verified by comparing the operation data.Finally,the influence of the explosion-proof box on the current carrying capacity of the joint is analyzed.The cavity in the explosion-proof box greatly reduces the heat dissipation performance of the joint.Compared with cable body,the ampacity is reduced by about 37.1%,while the heat dissipation of the joint can be greatly enhanced by pouring the epoxy resin ab glue,The current carrying capacity is increased by nearly 41.1% compared with that without the epoxy resin ab glue.It can provide a reference for the development of operation strategy,which is helpful to the safe and stable operation of three-core cables.(3)The explosion response mechanism of three core cable intermediate joint in distribution network is studied.In view of the fact that the instantaneous release of huge energy in the process of arc explosion is interlinked with the principle of explosive explosion,the arc energy of intermediate joint is equivalent to TNT explosion energy,and the model of intermediate joint is reasonably simplified,and the arc impact simulation model of cable intermediate joint is established.(4)The dynamic response of the explosion-proof box under explosive impact is analyzed by explicit dynamics.On the basis of orthogonal experimental design,the law of structural parameters on its explosion resistance performance is further studied.The result indicates the shell thickness and the cavity diameter can effectively improve the explosion resistance performance,while the shell length and port diameter have little effect on it.To balance explosion resistance and heat dissipation,the design of 2200 mm in shell length,140 mm in port diameter,8mm in shell thickness,and 120 mm in cavity diameter is appropriate.Research results can provide a reference for explosion-proof box design and cable joint protection,which is beneficial to prevent the expansion of cable accidents. |
