The insulation layer of power cables is composed of various combustible materials, such as paper, oil, hemp, rubber, plastic, and asphalt. Therefore, cables are susceptible to fire and explosion. Below, we will explain six possible causes of fire and explosion in wires and cables:
1. Insulation damage leading to short circuits: The protective lead sheath of power cables can be damaged during installation or mechanically damaged during operation, causing insulation breakdown between phases or between lead sheaths. The resulting arcing can ignite the insulation and the cable's outer sheath.
2. Prolonged cable overload operation: Prolonged overload operation causes the operating temperature of the cable's insulation to exceed the maximum allowable temperature for normal heating, causing the insulation to age and dry out. This insulation aging and drying out typically occurs throughout the entire cable line. Due to aging and drying out, the insulation loses or degrades its insulating and mechanical properties, making it prone to breakdown and fire, even potentially igniting multiple locations along the entire length of the cable.
3. Oil dripping and leakage from oil-immersed cables due to height differences: Oil dripping and leakage can occur when oil-immersed cables are installed at large height differences. As a result of this oil runoff, the upper portion of the cable dries out due to oil loss. This increases the thermal resistance of the cable, causing the paper insulation to char and prematurely break down. Furthermore, as the oil from the upper portion flows downward, it creates space at the upper cable head, creating negative pressure, which makes the cable more susceptible to moisture absorption and dampness. The accumulation of oil in the lower portion of the cable creates significant static pressure, which promotes oil leakage from the cable head. Both moisture and oil leakage increase the chance of cable failure and fire.
4. Insulation breakdown in the intermediate joint box: The intermediate joints in the cable joint box oxidize, heat up, and leak during operation due to insufficient crimping, inadequate welding, or improper joint material selection. During the manufacture of the intermediate joints, the insulation agent injected into the intermediate joint box is of substandard quality, air holes are present in the box, and the cable box is poorly sealed or damaged, allowing moisture to enter. All of these factors can cause insulation breakdown, resulting in a short circuit and potentially causing cable explosion and fire.
5. Cable head combustion: Flashover ignition can occur due to moisture and dirt accumulation on the cable head surface, cracked cable head porcelain bushings, and insufficient spacing between lead wires. This can cause burning of the cable head insulation and lead wire insulation.
6. External fire and heat sources can cause cable fires: Fires in oil systems, explosions in oil circuit breakers, spontaneous combustion of pulverized coal in boiler pulverizing or coal handling systems, baking of high-temperature steam pipes, chemical corrosion from acids and alkalis, welding sparks, and other ignition sources can all cause cable fires.
