During the operation of optical and electrical cables, the most significant factor leading to performance degradation is moisture penetration. If water enters an optical cable, it can increase fiber attenuation; if it enters an electrical cable, it can reduce the cable's insulation performance, affecting its operation. Therefore, water-blocking units, such as water-absorbent materials, are designed into the manufacturing process of optical and electrical cables to prevent moisture or water penetration, ensuring operational safety.
The main product forms of water-absorbent materials include water-absorbent powder, water-blocking tape, water-blocking yarn, and swelling-type water-blocking grease, etc. Depending on the application site, one type of water-blocking material may be used, or several different types may be used simultaneously to ensure the waterproof performance of the cables.
With the rapid application of 5G technology, the use of optical cables is becoming increasingly widespread, and requirements for them are becoming stricter. Particularly with the introduction of green and environmental protection requirements, fully dry optical cables are increasingly favored by the market. A significant feature of fully dry optical cables is that they do not use filling-type water-blocking grease or swelling-type water-blocking grease. Instead, water-blocking tape and water-blocking fibers are used for water-blocking across the entire cross-section of the cable.
The application of water-blocking tape in cables and optical cables is quite common, and there is abundant research literature on it. However, there is relatively less research reported on water-blocking yarn, particularly on water-blocking fiber materials with super absorbent properties. Due to their easy pay-off during the manufacturing of optical and electrical cables and simple processing, super absorbent fiber materials are currently the preferred water-blocking material in the manufacture of cables and optical cables, especially dry optical cables.
Application in Power Cable Manufacturing
With the continuous strengthening of China's infrastructure construction, the demand for power cables from supporting power projects continues to increase. Cables are usually installed by direct burial, in cable trenches, tunnels, or overhead methods. They are inevitably in humid environments or in direct contact with water, and may even be immersed in water short-term or long-term, causing water to slowly penetrate into the cable interior. Under the action of an electric field, tree-like structures can form in the conductor's insulation layer, a phenomenon known as water treeing. When water trees grow to a certain extent, they will lead to breakdown of the cable insulation. Water treeing is now internationally recognized as one of the main causes of cable aging. To improve the safety and reliability of the power supply system, cable design and manufacturing must adopt water-blocking structures or waterproofing measures to ensure the cable has good water-blocking performance.
Water penetration paths in cables can generally be divided into two types: radial (or transverse) penetration through the sheath, and longitudinal (or axial) penetration along the conductor and cable core. For radial (transverse) water blocking, a comprehensive water-blocking sheath, such as an aluminum-plastic composite tape longitudinally wrapped and then extruded with polyethylene, is often used. If complete radial water blocking is required, a metal sheath structure is adopted. For commonly used cables, water-blocking protection focuses mainly on longitudinal (axial) water penetration.
When designing the cable structure, waterproof measures should take into account water resistance in the longitudinal (or axial) direction of the conductor, water resistance outside the insulation layer, and water resistance throughout the entire structure. The general method for water-blocking conductors is to fill water-blocking materials inside and on the surface of the conductor. For high-voltage cables with conductors divided into sectors, water-blocking yarn is recommended to be used as the water-blocking material in the center, as shown in Figure 1. Water-blocking yarn can also be applied in full-structure water-blocking structures. By placing water-blocking yarn or water-blocking ropes woven from water-blocking yarn in the gaps between the various components of the cable, the channels for water to flow along the axial direction of the cable can be blocked to ensure that the longitudinal water tightness requirements are met. The schematic diagram of a typical full-structure water-blocking cable is shown in Figure 2.
In the cable structures mentioned above, water-absorbent fiber materials are used as the water-blocking unit. The mechanism relies on the large amount of super absorbent resin present on the surface of the fiber material. When encountering water, the resin rapidly expands to十几 to几十 times its original volume, forming a closed water-blocking layer on the circumferential cross-section of the cable core, blocking the water penetration channels, and stopping the further diffusion and extension of water or water vapor along the longitudinal direction, thus effectively protecting the cable.
Application in Optical Cables
The optical transmission performance, mechanical performance, and environmental performance of optical cables are the most basic requirements of a communication system. One measure to ensure the service life of an optical cable is to prevent water from penetrating into the optical fiber during operation, which would cause increased loss (i.e., hydrogen loss). The intrusion of water affects the light absorption peaks of the optical fiber in the wavelength range from 1.3μm to 1.60μm, leading to increased optical fiber loss. This wavelength band covers most of the transmission windows used in current optical communication systems. Therefore, waterproof structure design becomes a key element in optical cable construction.
The water-blocking structure design in optical cables is divided into radial water-blocking design and longitudinal water-blocking design. The radial water-blocking design adopts a comprehensive water-blocking sheath, i.e., a structure with aluminum-plastic or steel-plastic composite tape longitudinally wrapped and then extruded with polyethylene. Simultaneously, a loose tube made of polymer materials like PBT (Polybutylene terephthalate) or stainless steel is added outside the optical fiber. In the longitudinal waterproof structure design, the application of multiple layers of water-blocking materials is considered for every part of the structure. The water-blocking material inside the loose tube (or in the grooves of a skeleton-type cable) is changed from filling-type water-blocking grease to water-absorbent fiber material for the tube. One or two strands of water-blocking yarn are placed parallel to the cable core strengthening element to prevent external water vapor from penetrating longitudinally along the strength member. If necessary, water-blocking fibers can also be placed in the gaps between the stranded loose tubes to ensure the optical cable passes strict water penetration tests. The structure of a fully dry optical cable often uses a layered stranding type, as shown in Figure 3.
Post time: Aug-28-2025