A.Types of cable waterproof structure:
For medium voltage XLPE insulated power cables, there are usually the following waterproof structures:
1. For single-core cables, semi-conductive water-resisting tape is wrapped around the insulation shield layer of the cable, ordinary water-resisting tape is wrapped around the metal shield layer, and then the outer sheath is extruded. The outer sheath material can be ordinary PVC or HDPE material with radial water-resisting function, depending on other performance requirements of the cable. For three-core cables, in order to ensure full contact of metal shielding, only single conductive water-resisting tape is wrapped outside the insulation shield. The water-resisting tape is no longer wrapped outside the metal shield. Depending on the waterproof performance requirements, the filling can be filled with ordinary filling or water-resisting filling. The inner lining and outer sheath materials are the same as those described in single-core cables.
2. Aluminum-plastic composite strip layer inside outer sheath or inner liner is used as waterproof layer.
3. Extrude HDPE sheath directly outside the cable.
For XLPE insulated cables above 110kV level, metal cladding is mainly used to make the cables waterproof. The greatest characteristic of metal sheath is that it is completely impermeable, so the cable with metal sheath has very good radial water resistance. The main types of metal cladding are hot-pressed aluminium sleeve, hot-pressed lead sleeve, welded wrinkle aluminium sleeve, welded wrinkle steel sleeve, cold-drawn metal sleeve, etc.
B.Waterproofing forms of cables:
The waterproofing methods of cables are generally divided into two types: longitudinal water blocking and radial water runoff. Longitudinal water-blocking yarn, water-blocking powder and water-blocking belt are commonly used for water-blocking. Their water-blocking mechanism is that these materials contain a water-expandable material. When water enters the cable end or from the sheath defect, the material will encounter rapid expansion of water to prevent further diffusion of water along the cable longitudinal. The purpose of Cable longitudinal waterproofing is realized. Radial water resistance is mainly achieved by extruding HDPE non-metallic sheath or hot pressing, welding and cold drawing metal sheath.
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