Causes and hazards of moisture in XLPE power cables

In urban power grid reconstruction 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. Cable dampness or water ingress reduces the insulation resistance of the cable, which is an important aspect of the cable line running accident.

Causes and hazards of cable flooding

(1) When the new whole cable is shipped from the factory, both ends are sealed with plastic sealing sleeves. However, after the construction site is used according to the actual situation, the remaining part is simply wrapped with plastic cloth to break the gap. It is placed in the open air and the seal is not good. For a long time, it will inevitably have water vapor infiltrated into the cable.

(2) When laying cables, it is necessary to frequently cross roads, bridges and culverts. Due to weather or other reasons, many waters are often accumulated in the cable trenches. In the process of laying, it is inevitable that the cable heads will be immersed in water. Because the plastic cloth is not tightly wrapped or damaged, the water enters the cable; in addition, when the traction and the pipe are worn, the outer sheath or even the steel shovel is sometimes scratched. This phenomenon is particularly prominent when using mechanical traction.

(3) After the cable laying is completed, the cable head is not produced in time due to the limitation of on-site construction conditions, so that the unsealed cable breakage is exposed to the air for a long time, even immersed in water, so that the water vapor enters the cable in large quantities.

(4) During the cable head making process (including the terminal head and the intermediate joint), the newly handled cable ends may accidentally fall into the accumulated water in the site due to the negligence of the construction personnel.

(5) In the normal operation of the cable, if a breakdown such as breakdown occurs for some reason, the water in the cable trench will enter the cable inside the fault point; in civil construction, especially when using large construction machinery It is not uncommon for a construction site to have cable breakage or breakdown due to various human factors. In the event of such an accident, cable insulation is severely damaged and the cable is also flooded.

After the cable enters the water, under the action of the electric field, aging will occur, and finally the cable will break down.