In urban power grid renovation projects, cables, especially polyethylene insulated power 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 reduces the insulation resistance of the cable, which is a few important aspects that cause operation accidents in the cable line.
Causes and hazards of cables being damp
(1) When XLPE insulated cable is shipped from the factory, both ends of the cable are sealed with plastic sealing sleeves. However, after a section of the cable is used according to the actual situation at the construction site, the remaining part is simply wrapped with plastic cloth to wrap the fracture. Placed in the open air and poorly sealed, over time, water vapor will inevitably seep into the cable.
(2) During cable laying, it is necessary to cross roads, bridges and culverts frequently. Due to weather or other reasons, a lot of water often accumulates in the cable trench. During the laying process, it is inevitable that the cable head will be immersed in water. , Because the plastic cloth is not tightly wrapped or damaged, water enters the cable; in addition, the outer sheath or even the steel armor is sometimes scratched when pulling and piercing the pipe. This phenomenon is particularly prominent when using mechanical traction.
(3) After the cable is laid, the cable head cannot be made in time due to the constraints of the site construction conditions, 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 ends sometimes accidentally fall into the stagnant water on site.
(5) In the normal operation of the cable, if breakdowns such as breakdown occur due to some reason, the water in the cable trench will enter the cable along the fault point; in civil construction, especially when large construction machinery is used It is not uncommon for cables to be damaged or broken down due to various human factors on construction sites in China. When such an accident occurs, the cable insulation is severely damaged, and water can enter the cable.
After the cable enters the water, under the action of the electric field, the aging phenomenon will occur, and finally the cable will break down.