MATHEMATICAL MODELING OF THE NONSTATIONARY THERMAL CONDUCTIVITY OF CABLE LINES LAID IN THE GROUND
At present, in the production of high-voltage cables with cross-linked polyethylene (XLPE) insulation on the surface of screens, as a rule, fiber-optic temperature sensors are mounted that are used to monitor cable lines in real time during their operation. In this case, the determination of the thermal state of the cable line by the temperature of the optical fiber is possible only using a mathematical model of non-stationary thermal conduction under conditions of changing current load. Research objective: to create a mathematical model for calculating and predicting the temperature of cable strand veins based on data on the environmental parameters, cable line design, and also the temperature in the screens obtained by measurement. Results: research is carried out on the example of a three-phase high-voltage cable line laid in the ground and consisting of three single-core cables with copper conductive conductors with XLPE insulation. Three ways of laying the cable line are considered: in the horizontal plane at a distance in the light equal to the diameter of the cable; in the horizontal plane close; triangle. A two-dimensional mathematical model of non-stationary thermal conductivity is proposed, the numerical implementation of which is carried out in the Ansys Fluent software package. Initially, as a result of solving the problem of stationary thermal conductivity, the nominal current load is determined by the value of the long-term allowable temperature for insulation from cross-linked polyethylene. As an initial condition for solving the problem of non-stationary thermal conduction, the temperature field obtained at a current of 70 % of the nominal value is used. Further, the current in the cable line changes stepwise in the range from 150 % of the nominal to 70 % and vice versa. In the process of numerical studies, the time to reach the maximum temperature to the specified levels is estimated and the change in the temperature difference between the conductive core and the screen is determined. Practical relevance: this mathematical model can be used to assess the temperature conditions of high-voltage cable lines with fiber-optic temperature sensors.