2. The insulation skin is hardened and cracked;
3. The contact resistance increases, and the joint heats up.
The main reasons for cable aging are as follows:
1. Long-term overload operation. Overload operation, due to the thermal effect of current, when the load current passes through the cable, it will inevitably lead to conductor heating, and at the same time, the skin effect of charge, eddy current loss of steel armor and insulation medium loss will also produce additional heat, thus raising the temperature of the cable.
2. Environment and temperature. The external environment and heat source where the cable is located will also cause the cable temperature to be too high, insulation breakdown and even explosion and fire.
3. External force damage. From the operation analysis in recent years, quite a few cable failures are caused by mechanical damage.
4. insulation is damp. Generally, it occurs at the cable joint in the direct buried or exhaust pipe. After a long time, water branches are formed under the action of electric field, which gradually damages the insulation strength of cables and causes failures.
5. Cable connector failure. Cable joint is the weakest link in cable line, and cable joint failures caused by direct negligence (poor construction) often occur.
6. chemical corrosion. When cables are directly buried in acid-base areas, the armor, lead skin or outer sheath of cables will often be corroded. The protective layer will fail due to long-term chemical corrosion or electrolytic corrosion, which will also lead to cable failure.