What if the cable is flooded? These 10 precautions are too important
What if the cable is flooded?Generally speaking, power cables cannot be flooded during production. The inside of the cables must be dried, and the flooded cables cannot leave the factory due to harsh electric field voltage tests.
Once the cable water, under the action of the electric field, will occur water tree aging phenomenon, resulting in cable breakdown.A water tree is a collection of Spaces between 0.1m and a few microns in diameter filled with water.The starting point of the water tree is the impurity and porosity in the insulation and the local high electric field formed by the non-uniform place on the interface between the insulation and the inner and outer semi-conductive layer.The development process of water tree is generally more than 8 years. The higher the humidity, temperature and voltage are, the more ions there are in the water, and the faster the development of water tree is.The water directly enters the low-voltage power cable, causing the corrosion of steel strip, copper strip and other metals and the decline of insulation performance.When water passes through the insulation, it will cause the breakdown of the cable and even the explosion.
Newly bought into the tube cable, its both ends are sealed with plastic seal sleeve, but after using a section, the rest is wrapped with plastic paper, with a rope outside a tie, sealing is not good, a long time, water vapor will infiltrate the cable.
2、When cables are laid
When the cable is laid, the cable end wrapped in plastic paper is sometimes immersed in water, so that the water enters the cable.In the traction and penetration of the tube, sometimes the outer sheath rupture phenomenon.
After laying, the cable head is not made in time, so that the unsealed cable end is exposed to air for a long time, or even immersed in water, so that a large amount of water vapor into the cable.
4、Cable head when making
When the cable head is made (including the terminal head and the intermediate joint), the cable end will sometimes slide into the cable well with water due to the desire of the maker.
5、Cable running time
In the operation of the cable, when the breakdown of the intermediate joint occurs, the water in the cable well will enter the cable along the gap.At a construction site, cable damage or breakdown caused by external forces, can also occur cable water.
The treatment of cable water
It is very difficult to dry the cable after it is filled with water (such as hot nitrogen pressure drying), and the corresponding equipment is generally not equipped.In practice, if the cable R6 is flooded, we just cut off the front end for a few meters. If the whole cable is flooded, we cannot take it.Therefore, the prevention of cable water inlet should take the following measures:
1、Cable ends should be sealed
Sawed cable ends, whether piled up or laid, should be sealed with plastic (cable seal sleeve) to prevent moisture infiltration.
2、Timely production of cable head
The cable head should be made in time after the wires are laid.
3、When you buy cable
Must choose the quality of the factory.Because the impurities and pores in the insulation are the starting point of water tree, the quality of cable is very important to prevent the aging of water tree.
4、Strengthen the management of cable head manufacturing process
Once the cable water, the early breakdown phenomenon is often the cable head, so the wire head made well, can extend the overall life of the cable.For example, when the cable is stripping the semiconductor layer, we cut several lines vertically on the semiconductor layer, and then peel off the semiconductor like sugarcane.But in the use of the knife, if the cut is too deep, it will hurt the insulation layer, water tree production opportunities.In addition, when soldering, because can not find the power supply, will directly use the torch to melt soldering, at this time, the flame will damage the copper shielding layer and insulation layer, so to eliminate this phenomenon, the correct way can be configured UPS, because soldering time is generally only 10min, power is not more than 500W.
5、Adopt cold shrink cable head
Cold shrink silicon rubber cable accessories, easy to make, no blowtorch, no soldering.Moreover, the silicon rubber cable attachment is elastic and tightly attached to the cable, which overcomes the shortcoming of thermal shrinkage material (thermal shrinkage material is not elastic, and in the process of thermal expansion and cold contraction of the cable, there will be a gap between the cable and the cable body, which provides convenience for the development of the water tree).
6、PVC plastic double wall corrugated pipe
The tube is corrosion-resistant, the inner wall is smooth, the strength and toughness are good, so when the cable is buried directly, the damage of cable sheath can be greatly reduced.