Study On Thermal Circuit Model Of10kV Three Core Cable Conductor Temperature Calculation And Its Engineering Application

Urban power distribution network cable is the important part of urban power grid, but it’sdifficult to manage and control it. The standard of current carrying capacity of10kVthree-core cable in distribution network is particularly conservative and lack of scientific. Inview of the situation of increasing cities loads, it has to abandon the standard during theruntime and often overload. If it does not give a reasonable standard of current carryingcapacity of three-core cable in time, it’s easy to cause overload phenomenon more and moreserious. Then cable core will be overheated and it will result in accelerating insulation agingand great curtailment of cable life. When it is serious, some major accidents will occur, suchas insulation breakdown, fires and so on. How to accurately calculate the temperature of cablecore in real time in running distribution network is of great significance for improving theoperational reliability of the cable in distribution network, making full use of current carryingcapacity of cables and pecking load shifting of the load of large cities in future.At present, at home and foreign, the studies on the current carrying capacity of cablesmostly concentrated in the single-core high-voltage cables. There are several ways tocalculate core temperature of single-core high-voltage cables by skin temperature, and theyhave been complete. However, because of differences of structure, laying way, load type,operation mode and management between three-core cable and single-core cable, the set ofthe current carrying capacity of three-core cables is basically dependent on experimentalstudies on simulating the real operating environment, or adding the coefficient correction onthe basis of the thermal circuit model of single-core cable, and the thermal circuit model,which is specifically for the characteristics of the three-core cable structure and the heattransfer, have not been reported. In addition, at present, the load characteristics of three-corecable are diverse by multi-panel coils or cable duct, and the load of all cables is almostunlikely to peak simultaneously. If it limits current carrying capacity to run with reference toIEC standards, it will certainly result in a huge waste of the transmission capacity of the cablein distribution network; but if it ignores the standard and operates under overload in long term,it will cause cable fault, blackouts and huge loss. This paper combines with the actual operation of three-core cable in distribution networkin Guangzhou and deeply research the research status of the calculation methods on thecurrent carrying capacity of three-core cable and conductor temperature at home and abroad.According to the characteristics of heat transfer and the shape of three-core cable, establishthe thermal circuit model for calculating conductor temperature of a three-core cable, anddiscuss further the dynamic characteristics of the parameters of thermal resistance in thismodel. So it realizes accurate calculation of conductor temperature by the real-time surfacetemperature of the cable and the load. In order to verify precision of the model, establish anexperimental system for three-core cable current lifting, In order to verify precision of themodel, establish an experimental system for three-core cable current lifting, design theexperiment for step-index current lifting of three-core cable, and compare the experimentalvalues with the theoretical values of conductor temperature calculation through thermal circuitmodel. These verify the reliability of the thermal circuit model. By analyzing data error,explore the actual transient thermal characteristics of the thermal resistance of three-corecable during the heat transfer process, and correct the thermal circuit model parameters. Onthis basis, the established three-core cable thermal circuit model is used to calculate theemergency response time when there is fault that a line contains twice load and designexperiments for emergency up-flow load under different initial load. Compared theoreticaland experimental values, prove further the reliability and practical value of the model.