Discussion on Damage of Water to Spiral Cable
In general, the water immersed in the spiral cable after the main impact of the spiral cable conductor and insulation. The conductor is in a stable state of normal operation, the conductor temperature is maintained at above 60 ℃, if there is water immersion will lead to oxidation, increase the contact resistance between the single conductor to increase the spiral cable core resistance, resulting in spiral cable loss increased. In terms of insulation, although polyethylene is extremely difficult to dissolve in water non-polar hydrophobic material, but it is a crystalline phase and amorphous phase composed of semi-crystalline polymer. Crystalline phase structure is compact, grain boundary defect is weak, the amorphous phase of the molecular arrangement of loose, there is a large gap between molecules. Microporous focusing may also occur at the interface between the crystalline phase and the amorphous phase. Water is a polar molecule. Under the action of an alternating electric field, the interaction of the water molecules dip between the dip 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 Material. XLPE molecular structure also has the same problem, while XLPE has more cross-linked products as impurities, so XLPE in the alternating electric field also has a larger water absorption. After the cross - linked polyethylene and polyethylene insulated water, the role of the electric field in the formation of water branches, insulated crystal phase and amorphous interface interface to become a priority channel for the development of water. The production of water tree branches will increase the insulation medium loss, while reducing the insulation resistance and insulation breakdown voltage, speed up the aging rate and shorten the service life of the spiral cable. More seriously, the water tree branches under the action of the electric field or after a long period of oxidation, transformation, and ultimately not only in the water branch of the tip of the production of electric tree branches, their own may also be transformed into electric tree branches. As we all know, there is a continuous expansion of the electronic tree branch of the local discharge, will lead to spiral cable insulation in the short term was breakdown, seriously affecting the use of spiral cable reliability.
Early prevention of spiral cable insulation in the production of water branches, mainly to consider the improvement of XLPE, the use of adding voltage stabilizer and other additives to inhibit the production of water branches, this has a certain effect, but did not fundamentally solve the problem. To prevent moisture and moisture into the XLPE insulated power spiral cable, is to prevent the insulation in the water tree branches of the fundamental way.
In view of the XLPE spiral cable water, damp after the operation of the reliability of the spiral cable and the impact of life at home and abroad has developed a lot of spiral cable water blocking technology. These water blocking technologies can be categorized as follows:
(1) according to the water blocking material taken, can be divided into active water blocking technology and passive water blocking technology;
(2) According to the use of the water blocking mechanism, can be divided into vertical water blocking technology and radial water blocking technology.
In recent years, China has developed a large number of patents in the industrial production of water-blocking spiral cables.
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