Electrical engineering & Electromechanics (Jun 2020)
PROVIDING TECHNICAL PARAMETERS OF RESISTIVE CABLES OF THE HEATING FLOOR SYSTEM WITH PRESERVATION OF THERMAL RESISTANCE OF INSULATION
Abstract
Introduction. The main purpose of resistive cables is to convert the current flowing through the cable into heat. The maximum operating temperature of the conductive core should not exceed 100 °C. Power output per cable per unit length (nominal specific electrical power per 1 m of heating cable at rated line voltage per 1m cable) is the main technical parameter of these cables. The heat released by the conductivity of the core current, taking into account the change in the resistivity of the core material from temperature, is directly proportional to the square of the linear voltage drop across the core, and inversely proportional to the linear resistance of the core. Typical heat dissipation in such cables does not exceed 10 W/m, provided the cable is placed in the air. Purpose. Determination of the specific power of the cable system when varying the thickness of the insulation and the protective polymer shell, provided the thermal stability of the insulation on the basis of thermal balance between the power released in the core and the power released into the environment from the surface of the resistive heating. Methodology. The calculation of the linear heat flux is performed in two steps: when changing the radius of insulation (thickness of insulation) and the constant thickness of the protective polymer shell; at constant thickness of insulation and change of radius of the protective polymer jacket . The highest values of linear heat flux at (70-90) W/m are achieved for the optimum design of a single-conductor resistive cable from a conductive core in the range of 0,4 mm to 1,6 mm when varying the thickness of the cross-linked polyethylene insulation and protective sheath based on polyvinyl chloride plastic. The specific power of heating resistive cables, provided the thermal stability of the crosslinked polyethylene insulation is determined based on the thermal balance between the power generated in the core and the power dissipated from the surface of the cable into the air. Practical value. The thickness of the insulation and the linear voltage of the heating resistive cable, depending on the material of the core, providing thermal stability of the insulation are substantiated. The methodology of substantiation of specific power, which corresponds to thermal stability of heating resistive cables on the basis of thermal balance, can be applied to both the floor heating system and other areas of application of heating cables.
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