Cables, especially polyethylene insulated power cables, have been widely used in urban power grid reconstruction projects. However, due to the special characteristics of cables, the installation, operation and maintenance of cables have special requirements. Cable moisture or water to reduce the insulation resistance of the cable is caused by several important aspects of the cable line to occur in the operation of the accident.
Cable moisture into the water causes and hazards
(1) new into the whole cable in the factory, both ends of the use of plastic sealing sleeve sealed, but in the construction site according to the actual situation with a section after the rest of the part with a simple plastic wrap around the break, due to the usual open-air placement and sealing is not good, a long time, there will inevitably be water vapor infiltration of the cable.
(2) cable laying, often need to cross roads, bridges and culverts, etc., due to weather or other reasons, the cable trench often accumulates a lot of water, the laying process, it is inevitable that there will be a cable head immersed in the water due to the plastic wrap is not tight or broken and make the water into the cable; In addition to hauling and threading pipe, sometimes also occurs when the outer sheath or even the steel armored was scraped phenomenon, when the use of mechanical hauling When using mechanical traction, this phenomenon is particularly prominent.
(3) After the cable laying is completed, the cable head is not made in time due to the constraints of on-site construction conditions, so that the unsealed cable breaks are exposed to the air for a long time, or even immersed in the water, so that a large amount of water vapor enters into the cable.
(4) In the process of cable head production (including terminal heads and intermediate joints), due to the carelessness of 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 for some reason breakdown occurs, such as faults, the water in the cable trench will be along the fault point into the internal cable; in civil construction, especially in the use of large-scale construction machinery in the construction site, due to a variety of human factors caused by the cable breakage or breakdown accidents, is also not uncommon. When such an accident occurs, the cable insulation was seriously damaged, will also cause the cable into the water.
After the cable enters the water, under the action of the electric field, the aging phenomenon will occur, and finally lead to the breakdown of the cable.