Analysis of the causes of insulation breakdown of wires and cables

Breakdown refers to the damage of the original insulation function caused by external force damage, (extrusion, lightning stroke, etc.) of the insulation layer, aging of insulation data, etc., and the original insulation function is lost. During the operation of the AAC Cable, the core wire is discharged from the core to the core wire, the core wire is used to the outer protective steel strip and the ground to release power, thus forming the short circuit to ground. The main reasons for insulation breakdown of wires and cables are as follows.

Mechanical damage
Because heavy objects hurt the cable, the excavator accidentally injured the cable, the cable bent over Ambassador insulation during laying, and the cable was severely squeezed during shipment, which damaged the insulation and protective layer. Because the bottom sunk and buried cable was too tensile, the insulation was damaged, and even the cable would be pulled off. The overhead cable can be used to prevent mechanical damage of cables. If the cables are laid along the wall, they shall be covered, and the ground shall be marked with obvious signs, and the soil shall be stopped nearby the cable line in time.
Improper construction
Because of the poor construction method and poor quality of data used, the weak links of cable head and center break down, leading to the breakdown of insulation layer. To prevent this phenomenon, the quality of the cable head device should be improved. During the manufacture and installation of cable head, the insulation bag should be tight and no open space should be presented. Before epoxy resin and quartz powder, strict drying treatment shall be carried out to prevent bubbles and moisture from entering the cable head, and the insulation treatment at the edge of lead sheath shall be strengthened.
Insulation is damp
Because of the poor construction technology of cable head, water may invade the cable or the sheath inside the cable is damaged, and water will enter. Lead wrapped cable is laid near the source, and fatigue and cracking occur due to a long stir. The cable skin is corroded and becomes empty. Because of the poor quality of manufacture, there are holes or cracks in the lead package. In view of these conditions, the protection of the outer layer of the cable should be strengthened and a layer of asphalt shall be applied to the outer cover at regular intervals.

Over voltage
Because of the over-voltage or internal overvoltage, the insulation layer is broken down, especially the over-voltage in the system will form multiple cables to be broken down at the same time. In this regard, lightning arresters should be installed to improve the technology level of active protection of the system.
Insulation aging
During the long-term operation of the cable, the electrical and mechanical functions of the insulation data are deteriorated due to poor heat dissipation or overload, which makes the insulation layer brittle or cracked. If so, preventive voltage withstand test of cable incoming shall be conducted according to the period. If the cable insulation drop cannot meet the requirements of safe operation, new cables shall be replaced.

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