In the renovation project of Urban Power network, cable, especially polyethylene insulated power cable, has been widely used. However, because of the particularity of cable, the installation, operation and maintenance of cable have special requirements. The loss of cable insulation resistance caused by damp or water in cables is an important aspect of the operation accident of cable line.
Causes and harms of damp and influent of cable
(1) When the whole new cable is in the factory, both ends of the use of plastic seals sealed, but in the construction site in accordance with the actual situation used after a period of time, the rest of the section with plastic sheeting simple to bandage the fracture, due to the usual open-air display and sealing is not good, days, it is inevitable that there will be water vapor infiltration cable.
(2) When the cable is laid, it is necessary to cross roads, bridges and culverts frequently, due to the weather or other reasons, the cable trench also often accumulated a lot of water, laying process, the inevitable cable head will be immersed in the water, because the plastic sheeting is not tight or damaged to make water into the cable; In addition to traction and pipe-piercing Sometimes the outer sheath or even the steel armour is blown bad phenomenon, when the use of mechanical traction, this phenomenon is particularly prominent.
(3) After the completion of the cable laying, due to the site construction conditions to limit the timely production of cable head, so that the failure of the sealing treatment of the cable fracture long-term exposure to the air, or even immersed in water, so that a large number of moisture into the cable.
(4) in the production of cable head (including terminal head and the middle connector), due to the negligence of the construction staff, the new treatment of the cable end sometimes accidentally fell into the site of stagnant water.
(5) in the normal operation of the cable, if the breakdown occurs for some reason, the water in the cable trench will enter the cable inside the fault point. In civil construction, especially in the use of large-scale construction machinery, the construction site, due to a variety of man-made factors caused by cable breakage or breakdown accident, is not uncommon. When such an accident occurs, the cable insulation is severely damaged and the cable is flooded.
After the cable water, under the action of the electric field, aging phenomenon will occur, and finally lead to cable breakdown.