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Analysis of the causes of wire and cable aging

by:AAA     2021-03-25
The most direct cause of wire and cable aging failure is insulation degradation and breakdown. Many factors cause conductive-sensitive insulation degradation. According to actual operating experience, it can be summed up as the following situations.

1) Reasons for cable aging: external force damage.
Judging from the operation analysis in recent years, especially in the high-speed economic development of Haipudong, a considerable number of cable failures are now caused by mechanical damage. For example, non-standard construction during cable laying and installation can easily cause mechanical damage; civil construction on directly buried cables can easily damage lines in operation. l Sometimes, if the injury is not severe, it will take months or even years to cause the damaged part to be completely broken down and form a fault. Sometimes, a short-circuit fault may occur if the damage is severe, directly affecting the electric power unit's safe production and the power user.

2) Reasons for cable aging: insulation is damp.
This situation is also prevalent and generally occurs at the cable joints in direct burial or piping. For example, unqualified cable joints and joints made in humid weather conditions will cause the joints to enter water or water vapor, and water branches will form under the electric field's action for a long time, which will gradually damage the insulation strength of the cable and cause failure.

3) Reasons for cable aging: chemical corrosion.
The cable is directly buried in the area with acid and alkali, which will often cause the cable armor, lead skin, or outer sheath to be corroded. The protective layer suffers from chemical corrosion or electrolytic corrosion for a long time, resulting in the protective layer's failure and the reduction of insulation. The cable is faulty.

4) Reasons for cable aging: long-term overload operation.
Overload operation, due to the thermal effect of the current, the conductor heating will inevitably be caused when the load current passes through the cable. Simultaneously, the charge's skin effect, the recent eddy loss of the steel armor, and the insulation loss will also generate additional heat, which will increase the cable's temperature. During long-term overload operation, the excessively high temperature will accelerate the insulation's aging, and even the insulation will be broken down. Especially in the hot summer, the cable's temperature rise often leads to the first breakdown of the inadequate insulation of the line, so in the summer, there are more cable faults.

5) Reasons for cable aging: cable connector failure.
The cable joint is the weakest link in the cable line, and the joint cable failures caused by the personnel's direct fault (poor construction) often occur. In the process of making cable joints, if there are original nets such as insufficient joint crimping, low heating, etc., the insulation of the cable head will be reduced, which will cause an accident.

6) Reasons for cable aging: environment and temperature.
The cable's external environment and the heat source can also cause the cord to overheat, insulation breakdown, and even explosion and fire.

How to judge the aging of the wire?
1. Whether the current is leaking or even short-circuited to catch fire;
2. Hardening and cracks appear in the insulation;
3. The contact resistance increases, and the joint becomes hot.
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