The cables of the cable tray are mainly insulated by a layer of outer sheath. If the protection is not good, they will be corroded by external gas for a long time, and the insulation performance will gradually decrease. They will age and harden slowly, become brittle or fall off. At this time, they will not be able to play the role of insulation. The insulation layer on the outside of the cable is mostly made of plastic and rubber. Sometimes it is found that it is aging. What are the reasons? Then I'll take you to analyze this problem.
1. Insulation moisture.
Generally, this situation is also relatively common, which usually occurs at the cable joint in the directly buried or row pipe. For example, unqualified cable joints and joints made in humid weather conditions will make the joints water or mixed with water vapor, form water branches under the action of electric field, and gradually damage the insulation strength of the cable, resulting in failure.
2. Corrosion of chemical raw materials.
If the cable is directly buried in the area with acid-base effect, it will often cause the armor, lead skin or outer protective layer of the cable to be corroded. The protective layer will be subject to chemical corrosion or electrolytic corrosion for a long time, resulting in the failure of the protective layer, reduced insulation and cable failure.
3. Long term overload operation.
During overload operation, due to the thermal effect of the current, the conductor will be heated when the load current passes through the cable. At the same time, the skin effect of the charge, the eddy current loss of the steel armor and the loss of insulating medium will also produce additional heat, which will increase the temperature of the cable. During long-term overload operation, too high temperature will accelerate the aging of insulation and even the insulation will be broken down. Especially in the hot summer, the temperature rise of the cable often leads to the breakdown of the weak part of the cable insulation first. Therefore, there are many cable faults in summer.
4. Cable connector failure.
The cable joint is a weak link in the cable line. The cable joint failure caused by the direct fault of personnel (poor construction) often occurs. In the process of making cable joints, if there are original nets such as loose crimping and insufficient heating of joints, the insulation of cable heads will be reduced, resulting in accidents.
5. Environmental and temperature factors.
The cable bridge and the external environment and heat source around the cable will also cause excessive cable temperature, insulation breakdown, and serious explosion and fire.
6. External force damage.
At present, most cable faults are caused by mechanical damage. For example: the cable laying and installation is not standardized, which is easy to cause mechanical damage; Civil construction on directly buried cables is also easy to damage the cables in operation. In some cases, the damage of the cable is not serious at that time, and it may take months or even years before the breakdown of the damaged part may form a fault. In other cases, the cable with serious damage may have a short-circuit fault, which will directly affect the production and life of the cable bridge and power users.
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