Seawater-proof cables and technical difficulties

Waterproof function of submarine cable

When mechanical stress or external force causes damage to the cable sheath, insulation and joints, moisture or moisture will infiltrate along the longitudinal and radial gaps of the cable, reducing the electrical strength of the insulation. Therefore, most high-voltage submarine cables have longitudinal and Radial waterproofing measures.

The radial measures are mainly to wrap the semiconducting resistance water expansion tape on the outside of the insulating shield and the metal shield layer, and add a metal waterproof layer, that is, a metal sheath, on the outside of the metal shield layer. The electric field strength of the medium voltage power cable is relatively low, and aluminum-plastic composite Sheath, there are also only polymer sheath, high-voltage cables use lead, aluminum, stainless steel metal sealing sleeve. The polymer sheath is waterproof, but has a certain water absorption rate because its structure is mainly a semi-crystalline polymer composed of crystalline phase and amorphous phase. The structure of the crystalline phase is compact, the molecular arrangement in the amorphous phase is loose, and there are large gaps between the molecules. Under the action of the alternating electric field, the polar water molecules are constantly flipped back and forth, and can penetrate into the insulating material through gaps and grain boundary defects. When a polymer sheath is used, a water blocking agent with water absorption should be added to the sheath.

Longitudinal water blocking mainly adopts ① compression core; ② adding water blocking material between the wires and the shielding area of the cable core to block the diffusion channel of water in the cable core. Longitudinal water blocking is well filled with water blocking powder, its water absorption is dozens or even thousands of times its own, with high water absorption strength and high expansion rate. The further diffusion and extension of moisture and moisture minimize the length of the damped cable.