| To alleviate the current situation that the increasing difficulty in building the new power transmission corridors is against the rapid growth of power transmission demand,the cluster laying way is widely used in the new XLPE cable lines.In the design process of cluster laying cables,the cable ampacity decided by the IEC method or the national standard is used to guide the selection of conductor cross-section.But,the ampacity decided by the IEC method or the national standard is often a conservative value,which is not conducive to the efficient use of cable resources.In addition,the current researches on thermal rating and optimal selection of conductor cross-section of cluster laying cables have the following problems: 1)the existing researches often assume that all cables have the same load or artificially set the load value of each cable in the temperature distribution calculation of cluster laying cables.It is lack of the exploration of introducing the real load distribution condition of cluster laying cables into the thermal rating of cluster laying cables as the input.2)the accuracy of the thermal rating model for cluster laying cables proposed by the existing researches is insufficient.3)the existing researches lack the focus on the optimal selection of conductor cross-section for cluster laying cables.To solve the above-mentioned problems,the investigation on the thermal rating and optimal selection of conductor cross-section of cluster laying cables considering the load correlation among cable lines were carried out in this paper.The conductor temperature characterization function of cluster laying cables with the real load distribution as the input was established.Then,combined with the optimization investigations on the cable thermal rating model,the accurate calculation of the conductor temperature of cluster laying cables under different operation modes was realized.Based on the calculation results of the cable conductor temperature under different operating modes,the determination method for optimal selection of conductor cross-section of cluster laying cables was proposed.Compared with the selection results of conductor cross-section for cluster laying cables based on the IEC method or the national standard,the optimal selection results of conductor cross-section determined by the method proposed in this paper can reduce the investment cost of cable lines while ensuring the safe operation of cable lines.Details of the research are as follows:1)The conductor temperature characterization function and optimal selection method of conductor cross-section of cluster laying cables were studied.Firstly,taking the 110 k V cable grid as an example,the typical wiring modes and operation modes of the high-voltage cable grid were introduced.For the different wiring modes and operation modes of cable grid,the load correlations among each cable in the cluster laying cables were analyzed,and the method for determining the load distribution matrix of cluster laying cables was conducted.Subsequently,the load characteristics of cluster laying cables under different operating modes were discussed.Then,the conductor temperature characterization function of cluster laying cables with the load distribution matrix as the input was established to realize the thermal calculation of cluster laying cables under different operating modes.Finally,based on the conductor temperature characterization function of cluster laying cables,the optimal selection method of conductor cross-section of cluster laying cables considering the load correlation among cable lines was proposed.2)The optimization method for the steady-state thermal rating model of cluster laying cables and the determination method for the benchmark of optimal conductor cross-section of cluster laying cables were studied.Firstly,for the high-voltage cable with an air gap structure between the buffer layer and the aluminum sheath,the error caused by the use of IEC method in the steady-state thermal rating of cable body was analyzed.Considering the influence of the radial thermal expansion of the insulation,a correction algorithm for the thermal resistance of cable lining layer based on the dynamic form factor was proposed.Subsequently,combined with the error analysis of the IEC method applied to the external environment thermal response calculation of cluster laying cables,the optimized steady-state thermal rating model of cluster laying cables and the iterative solution method fully consider the mutual heating effect among cable lines were proposed.Finally,the general analytical form of the steady-state conductor temperature characterization function of cluster laying cables was deduced,and the steady-state thermal calculation of cluster laying cables considering the load correlation among cable lines was achieved.Furthermore,the method for determining the benchmark of the optimal conductor cross-section of cluster laying cables was presented.3)The thermal rating method for the ampacity bottleneck points of cable line considering the influence of the axial heat transfer and the correction method for the benchmark of optimal conductor cross-section of cluster laying cables were studied.Firstly,the heat transfer process at the ampacity bottleneck points of cable was analyzed.A quasi-three-dimensional thermal model of cable was established and the calculation methods for each parameter in the model were given.Based on the model,the improved thermal rating method for the ampacity bottleneck points of cable line was proposed.Subsequently,taking the cable joint as an example,the accuracy of the quasi-three-dimensional thermal model and the thermal rating method for the ampacity bottleneck points of cable line were verified.Finally,based on the thermal rating method for the ampacity bottleneck points of cable line,the judgment of whether the benchmark of optimal conductor cross-section of cluster laying cables can ensure the thermal stable operation of the ampacity bottleneck points of cable line was achieved.Furthermore,the method for correcting the benchmark of optimal conductor cross-section of cluster laying cables was presented.4)The optimization method for the dynamic thermal rating model of cluster laying cables and the inspection method of the modified benchmark of optimal conductor cross-section of cluster laying cables were studied.Firstly,the accuracy of the cable dynamic thermal model recommended by the IEC method used for cable dynamic thermal rating was analyzed,and it was pointed out that the equivalent thermal model of insulation becomes one of the main sources of error.The calculation formula for the dynamic allocation coefficient of cable insulation thermal capacitance was conducted,and the possible error accumulation phenomenon caused by adopting the constant allocation coefficient in cable dynamic thermal rating under continuous fluctuating load was explained.Subsequently,the improved cable dynamic thermal rating model based on partitioning insulation was established,and the solution of the dynamic conductor temperature characterization function of cluster laying cables was realized.Then,the optimized dynamic thermal rating method for cluster laying cables was proposed.Finally,based on the proposed dynamic thermal rating method,the judgment of whether the modified benchmark of optimal conductor cross-section of cluster laying cables can meet the requirement of the dynamic thermal stability test of cable was achieved.Furthermore,the method for inspecting the modified benchmark of optimal conductor cross-section of cluster laying cables was presented,and the optimal selection result of the conductor cross-section of cluster laying cables was determined. |
PDF Full Text Request