In the urban power grid reconstruction project, 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.
The cable insulation resistance is reduced due to damp or water, which is several important aspects of cable line operation accidents.
Causes and hazards of cable moisture inflow (1)
When the new whole cable leaves the factory, both ends of it are sealed with plastic sealing sleeves, but after using a section at the construction site according to the actual situation, the remaining part is simply wrapped up with plastic cloth, because it is usually placed in the open air and the seal is not good, it is inevitable that water vapor will seep into the cable after a long time. (2)
During cable laying, it is necessary to cross roads, bridges, culverts, etc. 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, and water will enter the cable due to loose or damaged plastic cloth;
In addition, when traction and threading, sometimes the outer sheath and even the steel bar are scratched, especially when mechanical traction is used. (3)
After the cable laying is completed, due to the limitation 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, and even immersed in water, so that a large amount of water vapor enters the cable. (4)In the process of making the cable head (Including terminals and intermediate joints)
Due to the negligence of the construction personnel, the newly treated cable ends sometimes accidentally fall into the accumulated water on site. (5)
In the normal operation of the cable, if breakdown and other faults occur for some reason, the accumulated water in the cable trench will enter the cable along the fault point;
In civil construction, especially in construction sites using large construction machinery, cable damage or breakdown accidents caused by various human factors are also common.
When such an accident occurs, the cable insulation is seriously damaged, which will also cause the cable to enter the water.
After the cable enters the water, under the action of the electric field, the aging phenomenon will occur, and finally lead to cable breakdown.