Self-supporting power overhead optical cable fittings
Aerial optical cables used in power systems are mainly three-dimensional self-supporting optical cables (ADSS), optical composite overhead ground wires (OPGW) and optical composite composite phases (OPPC). The reason why the power cable and the communication cable are separated is that the power cable is unique and independent, especially the use environment has a strong inductive power supply, which is difficult to carry out construction and maintenance. While more and more telecom operators are using power towers to build ADSS, they still need to comply with structural codes for power cables.
Self-supporting power overhead optical cable fittings - what are the characteristics of pre-twisted gold
1.1 Design principles and application characteristics
Self-supporting power overhead cables (ADSS and later OPGW and OPPC) use pre-twisted fittings. Pre-twisted fittings are a branch of overhead communication line fittings that consist of multiple single-strand helical aluminum-clad steel wires or pre-grouped galvanized steel wires.
Its design principle is similar to that of a spring, which is characterized by the helical groove being straightened when the pulling force is stretched, and the inner cavity shrinking when squeezed against each other, thereby increasing the clamping force (friction force) of the overhead cable. In the range of elastic deformation, the spring is stretched by force and the spring pitch is elongated. When the volume is constant, the outer diameter decreases.
When the holding force is greater than the pulling force, the spring extends along with the elongation of the object to be clamped, and the whole does not produce relative sliding, so as to achieve a balance between the two forces and tighten the object. During the long-term tension of the spring, the wire does not creep or plastically deform over time because it is still within the elastic deformation range. When the pre-twisted wire is wound on the optical cable, a tubular cavity is formed, and the inner diameter of the cavity is slightly smaller than the outer diameter of the optical cable.
At the same time, the inner wall of the cavity is covered with a layer of adhesive silicon carbide, which is used to increase the friction between the pre-stranded wire and the surface of the cable. When the cable is stressed, the pre-twisted wire "clamps" the cable tightly. When the force of the optical cable increases continuously, the inner thread of the pre-twisted wire is further combined with the surface of the optical cable, and the tighter the pre-twisted wire is, the smaller the optical holding force of the cable is.
The power sector first accepted pre-twisted fittings when using ADSS, showing very clear advantages, so later OPGW and OPPC were also expanded. The main application features of pre-twisted fittings are:
(1) The tensile pre-twisted clip has strong tensile strength, and its design strength is generally not less than 95% of the cable to calculate the breaking force:
(2) The stress distribution of the optical cable clamp is uniform and will not damage the optical cable:
(3) The installation is simple, the construction is convenient, the construction time is greatly shortened, and the installation can be completed by itself without the need for special tools for the tower:
(4) The material is generally made of aluminum-clad steel wire or galvanized steel wire, which has good corrosion resistance.
Main types and technical requirements
In the design of pre-twisted fittings, the design of sheet metal fixtures dominates. Tensile metal sheets are mainly used for the installation of cables in tensile towers, corner towers and terminal towers, and bear all the pulling forces of the cables. The technical requirements of sheet metal accessories are mainly:
(1) The effective length of the pre-stranded wire should not be less than 5 pitches;
(2) When the cable reaches the specified maximum working tension (40% RTS), the accessories should not cause any damage to the cable, and should not affect the transmission of optical signals:
(3) The failure load of the clip shall not be less than 95% of the rated breaking force of the cable.
Suspension accessories are mainly used for the suspension and support of optical cables on linear towers. It bears the dead weight of the cable (ice and snow) and disperses the radial compressive stress to protect the cable from abnormal cable bending radius and stress concentration.