Reasons for Insulation Breakdown of Power Cable
Breakdown refers to damage to the original insulation function of the cable due to external force damage (extrusion, lightning strike, etc.), aging of insulation data, etc. The cable conductor between the cable core wire and the outer protective steel strip of the cable discharges to the ground.
1. Mechanical damage
The cable is damaged by heavy objects, the cable is accidentally damaged by the excavator, the cable is bent too much during the laying process, the cable is severely squeezed during transportation, the insulation and protective layer are damaged, the bottom layer sinks, the directly buried cable is pulled too large, all These can cause insulation damage and even cable breakage. Overhead cables can be used to prevent mechanical damage to the cables. When the cable is laid along the wall, it should be covered, and the buried cable should be clearly marked, and soil should be prevented from taking soil near the cable line in time.
2. Improper construction
Due to the poor construction method and the poor quality of the data used, the cable head and the weak link in the center failed, resulting in the breakdown of the insulation. In order to prevent this phenomenon from happening, improve the quality of the device of the cable head. In the process of making and installing the cable head, the insulating bag should be tight and there should be no open space. Strict drying treatment is carried out before epoxy resin and quartz powder to prevent air bubbles and moisture from entering the cable head, and to strengthen the insulation treatment of the edge of the lead sheath.
3. Moisture barrier
Due to the poor construction process of the cable head, water penetrates into the cable interior, or damages the inner sheath of the cable. When the lead-clad cable is laid near the source of the earthquake, it is fatigued and cracked due to long-term fatigue. The cable sheath is corroded and emptied. There are pinholes or cracks in the leaded package due to poor manufacturing quality. In view of these situations, the protection of the outer layer of the cable should be strengthened, and a layer of asphalt should be brushed on the outer protective layer regularly.
Due to atmospheric overvoltage or internal overvoltage, the insulation layer is broken down, especially the overvoltage inside the system can cause multiple cables to break down at the same time. Therefore, lightning arresters should be installed to improve the technical level of active protection systems.
5. Insulation aging
During the long-term operation of the cable, due to poor heat dissipation or overload, the electrical and mechanical properties of the insulating material deteriorate, and the insulating layer becomes brittle or cracked. In this case, preventive withstand voltage tests should be carried out on the cables on a regular basis. If it is found that the insulation layer of the cable has dropped and cannot meet the requirements of operation, a new cable should be replaced.