What are the main reasons for wire and cable insulation breakdown?
Breakdown refers to the damage of the insulation layer of the cable due to external force (extrusion, lightning strike, etc.), deterioration of the insulation material, etc., which destroys the original insulation performance, loses the original insulation performance, and occurs from the core wire to the core wire of the running cable. Discharge to ground between the core wire and the outer sheath of the cable causes a short circuit to ground. The reasons for the breakdown of wire and cable insulation are as follows:
One is mechanical damage. The excavator accidentally pulled the cable due to the heavy object. When the cable is bent, the cable is bent too much and the insulation is damaged. The cable was severely crushed during transport, and the insulation and protection were damaged. The bottom layer of buried cables is too strong. Both will damage the insulation and even the cable. To avoid mechanical damage to the cables, overhead cables can be used. If the cable is laid along the wall, the ground should be clearly marked, and soil should be collected near the cable in time.
The second is improper construction. Due to the poor construction method and the poor quality of the materials used, the cable head and the weak link in the middle are broken, resulting in insulation breakdown. In order to prevent this phenomenon, the installation quality of the cable head should be improved. During the manufacture and installation of the cable head, the insulating bag should be tight and there should be no gaps. Epoxy resin and quartz powder are strictly dried before coating to prevent air bubbles and moisture from entering the cable head, and to strengthen the insulation treatment of the edge of the lead sheath.
The third is insulation damp. Due to the poor construction process of the cable head, moisture penetrates into the inside of the cable, or the inner protective layer of the cable is broken, allowing moisture to enter. Lead-clad cables are laid near the source of the earthquake, and fatigue cracks occur due to long-term vibration. The cable jacket is corroded to create voids. There are small holes or cracks in the lead pack due to poor manufacturing quality. In these cases, the maintenance of the outer layer of the cable should be intensified and a layer of bitumen should be regularly applied to the outer jacket.
The fourth is overvoltage. Insulation breakdown due to atmospheric overvoltage or internal overvoltage, especially when multiple cables are broken simultaneously due to overvoltage within the system. In this regard, lightning arresters should be installed to improve the technical level of automatic protection of the system.
Fifth, 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 broken. If this is the case, preventive withstand voltage tests should be performed on the cables periodically. It is found that the reduction of cable insulation cannot meet the requirements of safe operation, and the new cable should be replaced.