The cables that can be used normally in water are collectively referred to as water-resistant (waterproof) power cables.
When the cable is laid underwater, it is often immersed in water or wet places, requiring the cable to have a waterproof (resistance) function. That is, the requirement to have full waterproof function, to prevent water immersion in the cable caused by cable damage, and to ensure long-term stable operation of the cable underwater.
The difference between waterproof cables and ordinary cables is that ordinary cables can not be used in water.
Waterproof Cables are Divided into The Following Three Main Categories
1. Oil-paper insulated cable is the most typical waterproof cable.
Its insulation layer and conductors are filled with cable oil, and the insulation layer has a metal sheath (lead sheath or aluminum sheath) outside.
It is the cable with the best waterproof performance. In the past, oil-paper insulated cables were mostly used for submarine (or underwater) cables, but oil-paper insulated cables are subject to fall restrictions and have the trouble of oil leakage and inconvenient maintenance. Now they are used less and less.
2. Ethylene propylene rubber insulated cable is widely used in low and medium-voltage underwater transmission lines. It is due to its superior insulation performance, no “water tree” of worry. Waterproof rubber cable (JHS type) can operate safely in shallow water for a long time.
3. Cross-linked polyethylene XLPE insulated power cable has become the most widely used insulation material because of its excellent electrical, mechanical, and physical properties and simple production process.
It has a lightweight structure, large transmission capacity, easy installation, laying, and maintenance, and is not subject to fall restrictions.
However, it is particularly sensitive to moisture. If the insulation layer is wetted by water in the manufacturing and operation process, it is easy to occur “water tree” breakdown, which greatly shortens the service life of the cable.
Therefore, cross-linked polyethylene insulated cables, especially medium and high voltage cables at AC voltage, must have a “water barrier structure” when used in aqueous or humid environments.
The so-called “water barrier structure” includes radial water barrier structure and longitudinal water barrier structure.