Cables that can be normally used in water are collectively referred to as water blocking (waterproof) power cables. When the cable is laid underwater, it is often immersed in water or wet places, the cable is required to have the function of water prevention (resistance), that is, it is required to have the function of full water resistance, so as to prevent water from immersing into the cable and causing damage to the cable and ensure the long-term stable operation of the cable under water. The difference between waterproof cable and ordinary cable is that ordinary cable cannot be used in water.
Waterproof cables mainly fall into the following three categories:
An oil paper insulated cable is the most typical water-resistant cable. Its insulation and conductor are filled with cable oil, and there is a metal sheath (lead sheath or aluminum sheath) outside the insulation. It is the cable with the best water resistance. In the past, oil paper insulated cables were mostly used for submarine (or underwater) cables, but oil paper insulated cables are limited by the drop, which has the trouble of oil leakage and inconvenient maintenance. Now they are used less and less.
Second, the ethylene propylene rubber insulated cable widely used in medium and low voltage underwater transmission lines is due to its superior insulation performance without the worry of "water tree". Waterproof rubber sheathed cable (JHS type) can operate safely in shallow water for a long time.
Three crosslinked polyethylene (XLPE) insulated power cable has become the most widely used insulating material because of its excellent electrical, mechanical and physical properties, simple production process, light structure, large transmission capacity, convenient installation, laying and maintenance, and not limited by drop. However, it is particularly sensitive to moisture. If the insulation is soaked with water during manufacturing and operation, It is prone to "water tree" breakdown, which greatly shortens the service life of the cable. Therefore, XLPE insulated cables, especially medium and high voltage cables under AC voltage, must have "water blocking structure" when used in water environment or humid environment. The so-called "water blocking structure" includes radial water blocking structure and longitudinal water blocking structure.
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