Optimization Analysis Of Transient Thermal Circuit Model Of Power Cables

Conductor temperature online monitoring of running power cable is important mean tograsp the exact thermal state, and it’s also effective method for load dispatching, operationand maintenance, improving utilization of lines. In this paper, online monitoring model ofsingle core cable conductor temperature is researched based on the support of key scientificand technological projects of Guangzhou power supply Bureau limited, the major work is asfellow:1. Study on dynamic characteristics of thermal resistance between cable Al-sheath andconductor. Physical model of thermal resistance between Al-sheath and conductor is proposedand analysis of the impact of temperature on the thermal resistance is carried out. Curves ofexperimental thermal resistance changing with temperature is obtained through experiment,and quantitative analysis of its variation comparing theoretical calculated values andexperimental values for thermal resistance is done. It’s a basis for cable ampacity calculationsand online monitoring of conductor temperature.2. The research on Optimization modeling of cable transient thermal circuit model. Theconstruction of cable transient thermal circuit model and error of the model itself isdemonstrated in detail. The effect of cable layer material on heat transfer is obtained throughthe introduction of thermal diffusivity, and then focusing on the insulating layer of modelingfor optimization analysis. the thermal circuit models of the insulation subdividing by theequivalent thickness, the equivalent heat capacity, thickness in accordance with1:2:···n, andheat capacity in accordance with1:2:···n are constructed and the corresponding heat transfermatrix is constructed and solved, the matrix is then edited into a Matlab programs to achievethe arbitrary number of subdivision of insulation for calculating conductor temperature, andthe experiment of cable loading current to rise temperature is conducted to validate the model.Quantitative analysis to research the effect of insulation layers on model error is completedand the optimal model is filtered out.3. Effect of the sampling frequency and the error of the model structure. Based on theanalysis of the thermal time constant of the cable, transient thermal circuit model transformedby the integral solution for the differential analysis is demonstrated through analyzing the rateof change of cable conductor temperature under different time steps through experiments.Based on the above four kinds of transient thermal circuit model, the integral solution of model is converted to finite difference solution focusing on the effect of sampling frequencyon model error and the influence of time step and model structure on error is obtained throughexperiments.