Different Types of Cable Waterproof Material
Different Types of Cable Waterproof Material
Blog Article
Cable waterproof material can roughly divided into two categories, active water blocking and passive water blocking material. Active water blocking uses the water-absorbing and swelling properties of active water blocking materials. When the sheath or joint damaged, the water-blocking material expands when it encounters water. Which limiting the penetration of water in the channel. Such materials include water-absorbing and swelling ointment, water blocking tape, water blocking powder, water blocking yarn, water blocking rope, etc. Passive water-blocking uses the hydrophobicity of passive water blocking materials to block water from the damaged sheath. Such materials include petroleum filling paste, hot melt adhesive, thermal expansion ointment, etc.
What is a Passive Water Blocking Material?
Filling the cable with petroleum jelly, a passive water blocking material, was the main measure for water blocking of early power cables. This method can effectively keep moisture out of the cable, but filling with petroleum jelly has the following disadvantages:
- Greatly increases the weight of the cable;
- Causes the conductivity of the cable core to decrease;
- Petroleum fiber jelly seriously pollutes the cable joint and is difficult to clean;
- The complete filling process is not easy to control, and incomplete filling will lead to poor water-blocking effect.
What is an Active Water Blocking Material?
At present, the active water blocking materials used in cables are mainly water-blocking tapes, water-blocking powders, water blocking ropes and water blocking yarns. Compared with petroleum jelly, the basic characteristics of active water-blocking materials are strong water absorption and high expansion rate. They can absorb water strongly and expand rapidly to form a gel-like substance to block the water seepage channel, thereby ensuring the safety of cable insulation. In addition, active water-blocking materials are light and clean, easy to lay and connect, but active materials also have some disadvantages:
- Water-blocking powder is difficult to attach;
- Water-blocking tapes or water-blocking yarns will cause the outer diameter to become larger, heat dissipation is difficult, accelerate cable thermal aging and limit cable transmission capacity;
- Active water-blocking materials are generally more expensive.
Radial Water Blocking Structure
Polyethylene (inner sheath) waterproof isolation sleeve: The extruded polyethylene water-blocking layer combined with a moisture-absorbing cushion layer. Such as water-blocking tape to meet the longitudinal water-blocking and moisture-proof requirements of cables laid in general humid environments. The polyethylene material water-blocking layer is easy to implement in terms of technology, and no additional equipment is required.
Aluminum-plastic composite tape polyethylene bonding waterproof isolation sleeve: If the cable laid in water or in a particularly humid environment, the radial water-blocking ability of the polyethylene waterproof isolation sleeve is insufficient. For cables with high radial water-blocking performance requirements, a layer of aluminum-polyethylene composite tape now widely used to wrap the cable core. Its water-tightness is hundreds or even thousands of times higher than that of a single polyethylene. As long as the joints of the composite tape completely bonded and sealed, moisture is almost impossible to penetrate. The aluminum-polyethylene composite tape requires longitudinal wrapping and bonding processes, which requires a certain amount of capital investment and equipment modification.
Longitudinal Water Blocking Structure
In actual engineering, longitudinal water-blocking is more complicated to implement than radial water-blocking. Many methods have been used for longitudinal water blocking, such as changing the conductor to a compact structure, but the effect is not obvious, because there are gaps in the compact structure conductor, and water will still diffuse through siphon effect. To achieve true longitudinal water blocking, water blocking materials must be filled in the gaps of the twisted conductive core. The following two levels of measures and structures can be used to achieve longitudinal water blocking of cables:
- Use water-blocking conductors. Add water-blocking ropes, water-blocking powders, water-blocking yarns or wrapped water-blocking tapes when twisting and compacting conductors;
- Use water-blocking cable cores. In the cable core cabling process, fill water-blocking yarns, ropes and wrap semi-conductive water-blocking tapes or insulating water-blocking tapes.