Abstract
Evaluating environmental conditions that trigger fire-fighting equipment is one of the primary design tasks that have to be taken into account when engineering electrical systems supplying such devices. All of the solutions are aimed at, among others, preserving environmental parameters in a building being on fire for an assumed time and at a level enabling safe evacuation. These parameters include temperature, thermal radiation, visibility range, oxygen concentration, and environmental toxicity. This article presents a new mathematical model for heat exchange between the environment and an electric cable under thermal conditions exceeding permissible values for commonly used non-flammable installation cables. The method of analogy between thermal and electrical systems was adopted for modelling heat flow. Determining how the thermal conductivity of the cable and the thermal capacity of a conductor-insulation system can be applied to calculate the wire temperature depending on the heating time t and distance x from the heat source is discussed. Thermal conductivity and capacity were determined based on experimental tests for halogen-free flame-retardant (HFFR) cables with wire cross-sections of 2.5, 4.0, and 6.0 mm2. The conducted experimental tests enable verifying the results calculated by the mathematical model.
Highlights
Apart from the factors associated with the production and transmission of electricity by the domestic power grid, the parameters and quality of electricity supplied to consumers are impacted by environmental conditions where the consumers and the powering electricity are located
Constructing the model involved using thermal conductivity measurement data obtained from a designed test bench, which enabled measuring the temperature of the conducting wires in a cable laid on an open cable tray
The authors describe a mathematical model for cable heating along with a simulated cable temperature
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. The methodology adopted in the standard [9] does not assume the existence of an intermediate zone in which the wire, along a certain length, reaches a temperature that significantly exceeds the permissible values This does not provide a full picture of the temperature profile of the cable, so it is not sufficient for modelling the heating of the fire protection installations of halogen-free electric cables. The literature lacks mathematical models describing thermal phenomena in electric cables under an external temperature field, in which the full temperature profile of the cable is the result of the calculations This prompted the authors to develop a model of the thermal process of the cable by taking into account longitudinal and transverse losses with their distribution along the entire length of the cable (distributed parameters). Constructing the model involved using thermal conductivity measurement data obtained from a designed test bench, which enabled measuring the temperature of the conducting wires in a cable laid on an open cable tray
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