For medium voltage XLPE insulated power cables, usually there are several waterproof structures:
1 for single core cable, the insulating shielding layer wrapped semiconductive water resistance cable, the metal shielding layer wrapped outside of ordinary water blocking, then extruded outer sheath, the sheath material can be an ordinary PVC, can also be used with water resistance function of radial HDPE material, can be seen in other performance cable requirements. For the three core cable, in order to ensure the full contact of the metallic shield, only in the insulation shielding outside wrapped single conductive hose, metal shield no longer winding hose, depending on the different requirements of the waterproof performance, filled by normal filling or water blocking filling, lining layer and the outer sheath material with the single core cable in.
2 in the outer sheath or lining layer of the internal longitudinal cladding aluminum plastic composite layer as waterproof layer.
3 pack HDPE outer sheath directly outside cable.
For more than 110kV grade XLPE insulated cables, the metal protection layer is mainly used to meet the requirements of waterproof. The biggest characteristic of the metal protecting layer is that it is completely non permeable, so the cable with metal sheath has very good performance of radial water resistance. The main types of metal protective layer are: hot pressing aluminum sleeve, hot pressing lead sleeve, welded corrugated aluminum sheath, welded corrugated steel sleeve, cold drawn metal sleeve, etc..
Cable waterproof form:
Generally, there are two types of cable waterproof: longitudinal and radial. Watertight commonly used water blocking yarn, powder and water blocking resistance, water resistance mechanism of them is containing a water swellable material in these materials, when the moisture from the cable ends or enter from the sheath defect, this material will prevent the rapid expansion of water along the longitudinal cable further spread in the water, so as to realize the purpose of longitudinal waterproof cable. The radial water resistance is mainly realized by the extrusion of HDPE non-metallic protective layer or hot pressing, welding, cold drawing metal sheath.
Cable waterproof test basis:
Waterproof test cable, water resistance performance of the cable longitudinal current through IEC 60502-1997 ANNEX D (normative) or GB/T 12706.2-2002 appendix D (standard directory) to test and determine the permeability test; and the cable radial water resistance, the current is mainly determined by indirect methods, such as inspection or non HDPE non metallic sheath the metal sheath is defective, if the sheath is determined as well, so that the cable has good radial water resistance. But this method has a lot of users have raised some questions, also caused some disputes, the lack of convincing, so the cable manufacturers and users are in urgent need of a test method of cable radial water resistance make judgement, so you can avoid the manufacturers and users because of the lack of water resistance test method of radial cable the radial water resistance caused controversy.