Search Results (2)

Gas sensors can provide early warning of fires by detecting pyrolysis gas components in the sheaths of high-voltage cables. However, air humidity significantly affects the thermal decomposition gas production characteristics of the outer sheath of high-voltage cables, which in turn affects the accuracy of this warning method. In this paper, the thermal decomposition and gas production characteristics of the polyethylene (PE) outer jacket of high-voltage cables under different air humidities (20–100%) are studied, and the corresponding density functional theory (DFT) simulation calculations are performed using Gaussian 09W software. The results show that with the increase in humidity, the thermal decomposition gas yield of the PE outer jacket of high-voltage cables exhibits a decreasing trend. Under high-humidity conditions (≥68.28%RH), the generation of certain thermal decomposition gases is significantly reduced or even ceases. Meanwhile, the influence of moisture on the thermal decomposition characteristics of PE was analyzed at the micro level through simulation, indicating that the H-free radicals generated by moisture promote the initial decomposition of PE, but the subsequent combination of hydroxyl groups with terminal chain C forms a relatively stable alkoxy structure, increasing the activation energy of the reaction (by up to 44.7 kJ/mol) and thus inhibiting the generation of small-molecule gases. An experimental foundation is laid for the final construction of a fire warning method for high-voltage cables based on the information of thermal decomposition gas of the outer sheath. Full article

Cables are usually bent into a U-shape to cross obstacles during installation: this includes the upward-bending mode (UBM) and the downward-bending mode (DBM). An experimental study was conducted to investigate the combustion behavior of U-shaped cables with the above bending forms and different angles. The ignition point was set in the middle of the U-shaped cables and the temperature distribution, flame spread rate (FSR), mass loss rate (MLR), flame dimensional characteristics, etc. were measured and analyzed. The results showed that FSR and MLR are positively related to the bending angles, and the FSR is the highest in UBM 90°, close to 6.51 cm/min, which is four times higher than that in the bending angle 0° condition. In the UBM, the heat radiation and convection from the cable flame to the unburned region were more intense and the “eruptive fire phenomenon” occurred during the combustion process, leading to a sharp increase in the FSR in a short time. However, the thermal convection and radiation from the burning region to the unburned region were weakened in the DBM. Meanwhile, the molten outer sheath (PE) would flow along the cables, heating and igniting the unburned region in the DBM. In addition, the FSR, MLR, and peak temperature increased in the UBM compared to the DBM. The highest flame temperature occurred in UBD 90°, approximately 1023 °C. Full article