The insulating layer of power cable is usually composed of paper, oil, hemp, rubber, plastic, asphalt and other combustible substances. Therefore, the cable has the possibility of fire and explosion, and the main causes of fire and explosion of wires and cables are as follows:

1. Short circuit fault caused by insulation damage:

The protective lead sheath of power cable is damaged during laying or the cable insulation is mechanically damaged during operation, which causes insulation breakdown between cable phases or between lead sheaths, and the generated arc causes the burning of insulating materials and cable outer protective layer materials.

2. Long time overload operation of cable:

For a long time of overload operation, the operating temperature of the cable insulation material exceeds the maximum allowable temperature for normal heating, which makes the insulation of the cable aging and drying. This phenomenon usually occurs on the entire cable line. Due to aging and drying of cable insulation, insulation materials will lose or reduce their insulation and mechanical properties, so they are prone to breakdown and fire, or even fire at many places along the entire length of the cable.

3. Running and oil leakage of oil immersed cable due to height difference:

When the height difference of oil immersed cable is large, the cable may flow oil. As a result of flowing, the upper part of the cable will dry up due to the loss of oil, and the thermal resistance of this part of the cable will increase, causing the paper insulation to coke and break down in advance. In addition, as the oil in the upper part flows downward, space is made at the upper cable head and negative pressure is generated, which makes the cable easy to absorb moisture and damp the end. Due to the accumulation of oil at the lower part of the cable, great static pressure is generated, which causes the cable head to leak oil. Moisture and oil leakage of cables increase the probability of failure and fire.

4. Insulation breakdown of intermediate joint box:

The intermediate joint of the cable joint box is oxidized, heated and gummed during operation due to loose crimping, insecure welding or improper selection of joint materials; When making the cable intermediate joint, the quality of the insulating agent poured into the intermediate joint box does not meet the requirements. When pouring the insulating agent, there are air holes in the box, and the cable box is poorly sealed and damaged, causing moisture leakage. The above factors can cause insulation breakdown, form a short circuit, and cause the cable to explode and ignite.

5. Cable head burning:

As the surface of the cable head is affected by moisture and dirt, the porcelain bushing of the cable head is broken, and the phase distance between the outgoing lines is too small, resulting in flashover and ignition, causing burning of the surface insulation of the cable head and the insulation of the outgoing lines.

6. Cable fire caused by external fire source and heat source:

For example, the spread of fire in oil system, the spread of explosion and fire in oil circuit breaker, the spontaneous combustion of pulverized coal in boiler pulverizing system or coal conveying system, the baking of high-temperature steam pipes, the chemical corrosion of acid and alkali, welding sparks and other fires can all cause fire in cables.