The most direct cause of wire and cable aging failure is the breakdown of the insulation due to degradation. There are many factors that lead to the reduction of conductive insulation. 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 also easily damage cables in operation. l Sometimes if the damage is not serious, it will take months or even years to cause the damaged part to be completely broken down and cause a failure. Sometimes the damage is serious and a short-circuit fault may occur, which directly affects the safe production of the electric power and the power user.
2) Reasons for cable aging: insulation is damp. This situation is also very common, 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. For a long time, water branches will form under the action of the electric field, which will gradually damage the insulation strength of the power 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 protective layer to be corroded. The protective layer suffers from chemical corrosion or electrolytic corrosion for a long time, which causes the protective layer to fail and reduce the insulation. The cable is faulty. Chemical: the unit’s cable corrosion is quite serious
4) Reasons for cable aging: long-term overload operation. Overload operation, due to the thermal effect of the current, the conductor will inevitably heat up 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 insulation loss will also generate additional heat, which will increase the cable temperature. During long-term overload operation, excessively high temperature will accelerate the aging of the insulation, and even breakdown of the insulation. Especially in the hot summer, the temperature rise of the cable often leads to the first breakdown of the weak insulation of the cable, so in the summer, there are more cable faults.
5) Reasons for cable aging: cable connector failure. Cable joints are the weakest link in the cable line. Cable joint failures caused by direct faults (poor construction) by personnel often occur. In the process of making cable joints, if there are original nets such as insufficient joint crimping, insufficient heating, etc., the insulation of the cable head will be reduced, which may cause an accident.
6) Reasons for cable aging: environment and temperature. The external environment and heat source of the cable can also cause the cable to overheat, insulation breakdown, and even explosion and fire.
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