In urban power grid renovation projects, cables, especially PVC cables, have been widely used. However, due to the particularity of the cable, there are special requirements for the installation, operation and maintenance of the cable. Moisture or water in the cable will reduce the insulation resistance of the cable, which is a few important aspects that cause accidents in the operation of the cable line.
Causes and hazards of damp and water in cables
(1) When the PVC cable leaves the factory, both ends of the cable are sealed with plastic sealing sleeves. However, according to the actual situation of the construction site, after using a section of cable, the remaining part is simply wrapped in plastic sheet. Placed in the open and not well-sealed, over time, water vapor will inevitably penetrate into the cable.
(2) When laying PVC cables, they must often pass through roads, bridges and culverts. Due to weather or other reasons, a large amount of water often accumulates in the cable trench. During the laying process, the cable head will inevitably be immersed in water. , Because the plastic sheet is not tightly wrapped or damaged, water enters the cable; in addition, sometimes the outer sheath or even the steel armor will be scratched when the pipe is pulled and pierced. This phenomenon is particularly prominent when using mechanical traction.
(3) After the PVC cable is laid, due to the constraints of on-site construction conditions, the cable head cannot be made in time, so that the unsealed cable fracture is exposed to the air for a long time, or even immersed in water, causing a large amount of water vapor to enter the cable.
(4) In the process of making cable heads (including terminal heads and intermediate joints), due to the negligence of the construction personnel, the newly processed cable heads sometimes accidentally fall into the stagnant water on site.
(5) In the normal operation of PVC cable, if a failure or other failure occurs for some reason, the water in the cable trench will enter the cable along with the failure point; in civil construction, especially when large construction machinery is used, the On construction sites, it is not uncommon for cables to be damaged or broken due to various human factors. When such an accident occurs, the cable insulation layer will be severely damaged, and water will enter the cable.
After the cable enters the water, under the action of the electric field, the aging phenomenon will occur, which will eventually lead to the breakdown of the cable.
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