Characteristics of Short Circuit and Combustion in Electrical Cables Under Various External Heat Fluxes

Abstract

The insulation of electrical cables, exposed to external heat in a high-temperature environment, undergoes thermal decomposition and carbonization, resulting in the loss of insulation performance. Cables without insulation protection were prone to short circuits. Short circuits were one of the common ignition sources in electrical fires. However, research on the ignition of energized wires by arcs was not clarified. In this study, the standardized cone heater was used to simulate high-temperature conditions in order to investigate the occurrence of short circuits in energized cables within a high-temperature environment, as well as the characteristics and correlations of the combustion. The intensity of thermal exposure was accurately controlled through adjustments to the heat flux emitted by the cone heater. The short circuits in thermally exposed cables could be classified as a single arc or multiple arcs based on the fluctuations observed in voltage and current upon the occurrence of an arc. The results indicated that the minimum heat flux leading to a short circuit was 22 kW/m². A short-circuit arc became inevitable once the heat flux surpassed 25 kW/m². Notably, when the heat flux exceeded 26 kW/m², the probability of multiple short circuits within the conductor escalated significantly, reaching 83.7%. Compared to a single arc, multiple arcs exhibited a shorter initial occurrence time, a longer duration, and a higher probability of igniting cable insulation. The spread distance of combustion due to multiple arcs was primarily concentrated within the range of 23–28 cm. Furthermore, the maximum and minimum arc energies generated by multiple arcs were approximately three times higher than those generated by a single arc, respectively. This research provided valuable information for evaluating the fire hazards associated with different short circuits and determining the fire causes.