Introduction to the basic knowledge of OPGW fiber optic cable

Introduction to the basic knowledge of OPGW fiber optic cable

Background introduction

Optical fiber composite overhead ground wire (OPGW) is to put the optical fiber unit into the overhead ground wire, and organically combine the optical cable and the ground wire. On the premise of ensuring the original electrical and mechanical properties of the overhead ground wire, audio, Transmission of video, data and other information.Compared with other types of optical cables, it has high reliability; it is suitable for erection on power lines of various voltage levels, and the construction and installation are simple; it can withstand large stress, and has a strong ability to withstand strong wind and ice; it is protected by outer metal It can effectively avoid the communication line failure caused by lightning strike and short-circuit current in the traditional power communication system; it can accommodate a large number of optical fiber cores; the service life is long, generally more than 25 to 30 years.Due to the above advantages, in the power system, OPGW optical fiber communication has been widely used as an ideal communication means.

Theoretical and technical research

1) Optical fiber

Optical fiber communication is a communication method that uses laser as the information carrier and optical fiber as the transmission medium. Optical fiber is used as the transmission medium for optical fiber communication.

1. Basic structure of optical fiber

Optical fibers are drawn from two or more layers of transparent media, and generally include three parts: core, cladding and coating.

2. Types of communication fibers

Communication fibers can generally be divided into three categories: step-refractive multimode silica fibers, graded-refractive multimode silica fibers, and single-mode silica fibers. G.652 is the simplest single-mode fiber, which is also known as conventional single-mode fiber or standard single-mode fiber. Based on different transmission rates, G.652 fibers are subdivided into several categories:

G.652A fiber: The transmission distance of 10Gb/s system can reach 400km, and the transmission distance of 40Gb/s system can reach 2km.

G.652B fiber: The transmission distance of 10Gb/s system can reach more than 3000km, and the transmission distance of 40Gb/s system can reach 80km.

G.652C fiber: similar to G.652A fiber, but can work in the 1360~1530nm band.

G.652D fiber: similar to G.652A fiber, but can work in the 1360~1530nm band.

3. Optical fiber characteristic analysis

Optical fiber loss refers to the attenuation of optical power due to absorption, scattering and other reasons after the optical signal is transmitted through the optical fiber. The factors of fiber loss mainly include intrinsic loss, manufacturing loss and additional loss. Since the main component of the optical fiber core used in the communication system is silica glass, namely SiO2, and the silica fiber itself is not sensitive to temperature, in order to ensure the transmission performance of the optical fiber under extremely cold conditions, the performance of the optical fiber coating becomes The key factor. The properties of the coating material are easily changed with temperature, which makes the fiber loss increase in the environment where the temperature deviates from room temperature.

2) Optical cable

Although the coated and sheathed optical fiber has a certain compressive strength, it still cannot withstand bending, twisting, strong stretching and lateral pressure, etc., nor can it withstand the influence of harsh environments such as extreme temperature and humidity. Optical fiber cabling is the process of combining multiple optical fibers with various protective elements, packaging them into bundles, and forming optical cables.

1. The necessity of optical fiber cabling

The reason why the communication optical fiber needs to be cabled in practical applications is mainly due to the following reasons:

1) The installation, laying, inspection and maintenance of optical cables in the project are convenient.

2) The optical cable can better protect the optical fiber from the mechanical action of various forces during the laying process.

3) Optical fiber cabling can avoid the impact of harsh environments on the performance of optical fibers.

2. The structure of the optical cable

Optical cable is a practical light guide cable product that is combined with several optical fibers and various protective elements and packaged into a bundle. Usually, the optical cable is composed of four parts: the cable core, the strength element, the water blocking material and the sheath. Its basic structure is shown in figure above.

Power communication optical cables mainly include OPGW, OPPC, ADSS optical cables and optoelectronic composite cables. The supporting communication system of the power backbone network mainly uses OPGW optical cable. Its basic structure is composed of a metal protective tube twisted with metal (aluminum-clad steel, aluminum alloy, etc.) armored wires. Mechanical and electrical performance requirements for power lines.

3. Optical fiber filling paste

Optical fiber filling paste is a viscous semi-solid substance formed by dispersing one (or several) gelling agents in one (or several) base oils. The main function of optical fiber ointment is to prevent the optical fiber from being corroded by moisture. In addition, the fiber paste can also act as a cushion to buffer the mechanical forces such as vibration, impact, and bending on the optical fiber. In addition, the use of fiber paste can better ensure the mechanical properties of the optical fiber and prolong its service life.

4. Aluminum clad steel in OPGW cable

Aluminum clad steel is an important part of OPGW cable. Due to the low temperature brittleness of ordinary steel, the decrease of temperature has a great influence on its mechanical properties. As the temperature decreases, the yield strength (fy) and ultimate strength (fu) of the steel will increase, while the plasticity, elongation (δ), section shrinkage (Ψ) and other indicators of the steel will decrease.

Low temperature brittleness is the main indicator of the performance of steel at extreme low temperatures. The low temperature brittleness of steel is mainly affected by the following factors:

1) Alloying elements

2) Influence of metallurgical process on low temperature brittleness

3) Effect of heat treatment on low temperature brittleness

3) Optical cable fittings

1. Hardware metal components

The metal components of OPGW supporting fittings are mainly used to bear the load, and play the role of anchoring or supporting the OPGW optical cable and connecting the OPGW and the tower. Conventional OPGW fittings iron materials, such as Q235 steel, 35 steel, medium carbon cast steel, etc., are not low temperature resistant materials, and are not suitable for use in extreme low temperature conditions of -70 °C (aluminum is a non-cold brittle material, which can meet the requirements). Therefore, by studying the critical brittle transition temperature of steel, it is particularly important to select the appropriate material.

2. Polymer components for metal fittings

Polymer materials such as OPGW splice box disk fiber board, sealing ring and OPGW suspension clamp rubber block also have low temperature brittleness, and the brittle temperature can be used as an index to investigate. As the temperature decreases, the mobility of the polymer molecular chain becomes less and less, so the polymer material becomes hard and brittle. The embrittlement temperature refers to the temperature at which the material becomes brittle failure under the action of impact load, and is the lower limit of the temperature at which the material can be used normally. Below the embrittlement temperature, the material loses its flexibility, is brittle and easy to break, and cannot be used normally.