Experimental study on the flame spread behavior and heat transfer model of upward-bending cable

Due to the height differences during the power transmission, the upward-bending installation of cables is a common method. An experimental study was conducted to investigate the effect of the bending angle and number of cables on the flame spread behavior of upward-bending cables. Different bending angles (30°, 60°, and 90°) and a range of number of cables (1–5) were included in this work. The characteristic parameters, e.g., temperature on the cable surface, flame spread rate, flame feature, etc., were measured and analyzed. Results show that the flame spread rate of upward-bending cables gradually increases, as the number of cables increases. And the total flame length and flame-base length are positively related to the number of cables. Meanwhile, as the bending angle of upward-bending cables increases, the peak temperature on the cable surface increases, and the flame spread time decreases. The peak temperature on the cable surface is approximately 910 °C in the condition of five cables at 90° bending, which is 1.6 times as much as that in the condition of five cables at 0° bending. The faster flame spread rate increases in both the bending and inclined sections of upward-bending cables, with increasing bending angle. This is mainly because the larger the bending angle, the more intense the thermal convection and radiation on unburned cables, and the easier it is for the melt drippings to flow along the cable surface. Finally, within the current experimental range, a simplified heat transfer model of upward-bending cable was established.