The insulation layer of power cables is usually composed of various combustible substances such as paper, oil, hemp, rubber, plastic, asphalt, etc. Therefore, the cable has the possibility of fire and explosion. The main causes of fire and explosion of wires and cables are as follows:
1. Short circuit failure caused by insulation damage:
The protective lead sheath of the power cable is damaged during laying or the cable insulation is mechanically damaged during operation, causing insulation breakdown between cable phases or lead sheaths. The generated arc causes the insulation material and the outer protective layer material of the cable to burn and catch fire.
2. The cable is overloaded for a long time:
After long-term overload operation, the operating temperature of the cable insulation material exceeds the maximum allowable temperature of normal heating, causing the cable insulation to age and dry out. This phenomenon of insulation aging and drying usually occurs on the entire cable line. As the cable insulation ages and dries up, the insulation material loses or reduces its insulation and mechanical properties, making it prone to breakdown and fire, or even multiple simultaneous fires along the entire length of the cable.
3. Oil-immersed cables may drip or leak due to height differences:
When the oil-immersed cable is laid with a large height difference, oil dripping from the cable may occur. As a result of the flow, the upper part of the cable dries up due to the loss of oil. The thermal resistance of this part of the cable increases, causing the paper insulation to coke and cause premature breakdown. In addition, since the oil in the upper part flows downward, space is created at the upper cable head and negative pressure is generated, making the cable easy to absorb moisture and causing the end to become damp. The accumulation of oil in the lower part of the cable produces a large static pressure, causing the cable head to leak oil. Cable moisture and oil leakage increase the chance of failure and fire.
4. Insulation breakdown of intermediate joint box:
Due to loose crimping, weak welding, or improper selection of joint materials, the middle joint of the cable joint box will oxidize, heat, and flow during operation; when making the cable middle joint, the quality of the insulating agent poured into the middle joint box does not meet the standards. It is required that when pouring insulating agent, there are air holes in the box and the cable box is poorly sealed or damaged and moisture leaks in. The above factors can cause insulation breakdown, form a short circuit, and cause the cable to explode and catch fire.
5. Cable head burning:
Due to moisture and dirt on the surface of the cable head, the porcelain sleeve of the cable head is broken and the distance between the lead wires is too small, causing flashover and fire, causing the surface insulation of the cable head and the lead wire insulation to burn.
6. Cable fires caused by external fire and heat sources:
Such as the spread of fire in the oil system, the spread of oil circuit breaker explosion fire, spontaneous combustion of pulverized coal in the boiler pulverizing system or coal conveying system, baking of high-temperature steam pipes, chemical corrosion of acids and alkalis, welding sparks and other fires, all can cause cable damage. A fire occurs.
