The physical and predictive mathematical models of heat and mass transfer, phase transformations and chemical reaction have been developed to determine the necessary and sufficient conditions of inflammation and fire nascence at typical cable lines electrical overloads. The integral characteristics of study process complex - ignition delay times have been established according to cable lines electrical overloads modes. The temperature distributions in typical cable lines at overloads have been determined. The concentration variation characteristic ranges (which are sufficient for gas-phase ignition) of thermal decomposition components of cable sheaths at overloads have been adduced. The two-dimensional heat-and-mass transfer problem for a three-layer cable in the area of limited heat sink is solved. Thermal decomposition of the cable sheath and diffusion of thermal decomposition components and air were taken into account. Fire risk assessment of cable lines on overload in conditions of limited heat transfer is carried out. The dependence of ignition time delay for mixture of oxidized and thermal decomposition components from intensity of a current.
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