1、 Cable waterproof structure type:

　　For medium voltage XLPE insulated power cables, there are usually the following waterproof structures:

　　1. For single core cables, the semi conductive resistance water tape is wrapped around the insulation shield layer of the cable, the common water 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 blocking function, etc., depending on other performance requirements of the cable. For the three core cable, in order to ensure the full contact of the metal shield, only the single conductive resistance water tape is wrapped around the insulation shield, and the metal shield is no longer wrapped with the water blocking tape. Depending on the waterproof performance requirements, ordinary filling or water blocking filling can be used. The materials of the inner layer and outer sheath are the same as those described in the single core cable.

　　2. Aluminum plastic composite tape layer is longitudinally wrapped inside the outer sheath or inner liner as the waterproof layer.

　　3. Directly extrude HDPE outer sheath outside the cable.

　　For the nitrile series cables above 110KV, the metal sheath is mainly used to make the cables meet the waterproof requirements. The biggest characteristic of metal sheath is that it is completely impermeable, so the cable with metal sheath has very good radial water resistance performance. The types of metal protective layer mainly include: hot pressed aluminum sleeve, hot pressed lead sleeve, welded corrugated aluminum sleeve, welded corrugated steel sleeve, cold drawn metal sleeve, etc.

　　2、 Cable waterproof form:

　　The waterproof methods of cables are generally divided into two types: longitudinal water resistance and radial water resistance. Generally, water blocking yarn, water blocking powder and water blocking belt are commonly used for longitudinal water blocking. Their water blocking mechanism is that these materials contain a kind of water swellable material. When water enters from the cable end or the sheath defect, this material will rapidly expand in water to prevent further diffusion of water along the longitudinal direction of the cable, thus achieving the purpose of longitudinal waterproof of the cable. The radial water resistance of JHS waterproof cable is mainly realized by extruding HDPE non-metallic sheath or hot pressing, welding and cold drawing metal sheath.

　　3、 Basis of cable waterproof test:

　　Cable waterproof test method: at present, the longitudinal water resistance performance of the cable can be tested and judged by the water permeability test of IEC 60502-1997 annex D (normal) or GBT 12706.2-2002 Appendix D (standard catalogue); At present, the radial water resistance performance of the cable is mainly determined by indirect methods, such as checking whether the non-metallic sheath or the non-metallic sheath is defective. If these sheaths are determined to be complete, the cable is considered to have good radial water resistance performance. However, many users have raised some questions about this method and also caused some disputes, which are not convincing. Therefore, cable manufacturers and users urgently need a test method to determine the radial water resistance performance of cables, so as to avoid the disputes caused by the lack of radial water resistance test method between manufacturers and users.