Talking About The Damage Of Water To Cable

In general, the moisture and immersion of the cable mainly affect the conductor and insulation of the cable. When the conductor is in normal operation, it is in a state of thermal stability. The conductor temperature is basically maintained above 60 °C. If water is immersed, it will cause oxidation of the conductor, increase the contact resistance between the single wires of the conductor and increase the resistance of the cable core, resulting in an increase in cable line loss. 2]. In terms of insulation, although polyethylene is a non-polar hydrophobic substance that is extremely insoluble in water, it is a semi-crystalline high polymer composed of a crystalline phase and an amorphous phase. The crystal phase is compact in structure, the grain boundary defects are weak, the molecules in the amorphous phase are loosely arranged, and there are large gaps between the molecules. Micropore aggregation also occurs at the interface between the crystalline phase and the amorphous phase. The water molecules are polar molecules. Under the action of the alternating electric field, the dipoles of the water molecules are constantly flipped back and forth. The interaction of the diffusion force and the electric field force causes the water molecules to penetrate through the voids of the amorphous phase and the grain boundary defects of the crystal phase. In the insulation material. The same problem exists in the molecular structure of XLPE. At the same time, more cross-linked by-products in XLPE act as impurities, so XLPE also has a large water absorption under alternating electric field [3]. After the cross-linked polyethylene and polyethylene insulation absorb water, the water tree branches are formed by the action of the electric field, and the interface between the insulating crystal phase and the amorphous phase becomes a preferential channel for the water branch. The generation of water branches will increase the loss of insulating medium, reduce the insulation resistance and insulation breakdown voltage, accelerate the aging speed, and shorten the service life of the cable. What is more serious is that the water branches are oxidized and transformed under the action of electric field or not, and eventually they will not only form electric branches at the tip of the water branches, but also may turn into electric branches. It is well known that the electric tree branches are expanding. Partial discharge will cause cable insulation to be broken down in a short period of time, which seriously affects the reliability of cable use.

Early prevention of water tree branches in cable insulation, mainly considering the modification of XLPE, the use of voltage stabilizers and other additives to suppress the production of water branches, this has a certain effect but did not fundamentally solve the problem. Preventing moisture and moisture from entering the XLPE insulated power cable is the fundamental way to prevent the formation of water branches in the insulation [2].

In view of the influence of XLPE cable on water supply and reliability and life after cable damp, many cable water blocking technologies have been developed at home and abroad. These water blocking technologies can be roughly classified as follows: 1 According to the water blocking materials used, they can be divided into active water blocking technology and passive water blocking technology; 2 according to the water blocking mechanism adopted, they can be divided into longitudinal water blocking technology and radial Water blocking technology. Foreign countries have studied the development of water-blocking cable structures earlier. In recent years, China has made great progress in the industrial production of water-blocking cables. A number of patents have been published. This paper mainly summarizes and analyzes the structure of domestic open patented water blocking cable in recent years.