Contact Person : Linda Yang
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April 16, 2021
With the deepening of research and understanding of insulation water absorption and water tree, people are more and more aware of the importance of waterproof performance for medium and high voltage power cables. In areas where the groundwater level is high or rainy all the year round (such as the area south of the Yangtze River in China). More and more users have put forward waterproof requirements for cables. Most of the power cables are directly buried, so the cables are very likely to suffer from soil pressure and external force damage due to human factors.
From the perspective of laying forms, most foreign countries use metal protective sheaths for mechanical protection and waterproofing, or use cables covered with thin metal tapes and other waterproof layers. However, once this kind of cable is damaged, water will invade the inside of the cable from the damage, and then penetrate into the gap inside the cable (between conductor strands, extruded semi-conductive layer, shielding layer or metal sheath, etc.). Extend longitudinally along the cable, making long cables unusable. When the directly buried cable fails, a new cable is usually replaced at the point of the accident to restore the line. Therefore, once water penetrates into the cable, the water seepage distance should be as short as possible. In order to prevent water seepage after immersion, generally The gap part is used to wrap the water-absorbing swelling material, once it is immersed in water, the gap can be easily blocked.
Generally, the sheath material used in cables is polyvinyl chloride, and polyvinyl chloride molecules are polar. Polar water molecules can easily penetrate into the cable through the polyvinyl chloride layer. At present, it is necessary to realize the longitudinal water-blocking technology of the cable. There is no problem with the above, as long as a layer of water-blocking material made of water-tight material is added to the jacket. The currently commonly used method is to squeeze a layer of medium-high density PVC inner jacket in the PVC outer jacket or longitudinally wrap a layer of aluminum-plastic composite tape as the longitudinal water-blocking isolation jacket.
Polyethylene is easy to absorb water under an alternating electric field, which does not mean that the water tightness of the polyethylene material is not good. The water tightness of polyethylene material is hundreds of times higher than that of polyvinyl chloride. The extruded polyethylene water blocking layer and a layer of moisture-absorbing cushion (such as water blocking tape) can meet the longitudinal resistance of cables laid in general humid environments. Water and moisture-proof requirements. The use of polyethylene material in the water-blocking isolation sleeve is relatively simple in process, and it can be realized without adding any production equipment. Because the polyethylene layer is only used as a water-blocking layer without considering its mechanical strength and other factors, a good effect can be achieved when its thickness is 1.0~1.5mm during process design due to cost and process considerations.
Water blocking tape (yarn) can quickly swell in contact with water and reach a certain swelling height and can form a high-strength gel. It is an ideal active water blocking material, using water blocking tape, water blocking rope, and water blocking As a water-blocking material, yarn has simple process and convenient construction and high production efficiency. Therefore, this structure is generally welcomed by users and manufacturers. Because the contact surface between the single-core cable insulation and the sheath is relatively flat, as long as it is between the outer sheath and the core Wrap a layer of water blocking tape to achieve a good longitudinal water blocking effect. If there is a metal shield, you need to wrap the semi-conductive resistance hose on the inner side of the metal shield. Multi-core cables also need to be effectively filled with water-blocking ropes and water-blocking yarns in the gaps between the cable cores, and then wound with water-blocking tapes. For cables with armored layers, it is also necessary to use two layers inside and outside the armoring layer. A layer of water blocking tape is wrapped around each side.
Zhenglan Cable Technology can meet your special requirements in cable's water prevention. Welcome your inquiry.