Excess length control and precautions for typical structure of OPGW optical cable fittings
The influence of the remaining length of optical fiber on the service life of OPGW cable fittings is from production, construction, installation to operation. Due to the failure caused by the unreasonable remaining length of optical fiber, the service life of optical cable can be roughly divided into the following three stages.
1) Stage, within 1-3 years after the optical cable is erected, due to the impact of natural environment such as breeze vibration, galloping and temperature, the remaining length of optical fiber in different sections slightly deviates, and the remaining length of optical fiber will more conform to the line span and optical cable characteristics. Therefore, if the loss of OPGW fiber increases or even increases dramatically at this stage, it is mainly due to the lack of fiber surplus. The tension of OPGW cable in normal operation is generally 18% - 25% RTs. When encountering extreme weather such as strong wind and galloping, the maximum tension can reach 40%, and the elongation of optical cable is 4.45 kV, which is the lower limit of general surplus length design; when encountering maximum icing, the elongation of optical cable is 5.4 kV, that is to say, the elongation of optical cable should be increased by 0.9 ‰ according to 60% RTS, in addition, under the influence of extreme high temperature and low temperature thermal cycle and the change range of remaining length of optical cable, The operating temperature of OPGW can reach 40 ℃ in summer and - 30 ℃ in winter in some areas. In addition, under extreme winter conditions, the above two factors are superposed, that is, the fluctuation range of the remaining length of the optical cable is expanded to 1.7 ‰, which is a great test for the vast majority of optical cables. Attention should be paid to the design of optical cables in heavy ice area.
2) In the second stage, within 3-15 years after the cable is erected, due to the creep characteristics of the aluminum clad steel raw materials, the cable itself continues to grow, while the length of the optical fiber as a glass material has almost no change, so the remaining length of the optical fiber gradually decreases. When the remaining length of the production is too small, it will cause the increase of fiber loss.
The third stage is within 15-25 years after the optical cable is erected. Through the sampling and testing of the optical cable produced in different periods, it is found that the pastes change slowly with time. The whole process is to form small particles first, then gradually volatilize, decompose, dry and solidify. Sampling practice shows that the typical time of paste obvious denaturation is 18 years [9]. The acid value of mineral oil or synthetic oil-based composite fiber paste in close contact with optical fiber can increase the rate of hydrogen evolution. At the same time, the oxidation of oil paste has an impact on the structural stability of optical unit, which results in that the remaining length of optical fiber can not be adjusted freely under the influence of vibration, impact, bending, temperature difference change, micro morphology, etc. the fiber paste weakens the buffering effect on optical fiber and makes the use of optical cable Decreased life. The remaining length of optical fiber is the most important control parameter in OPGW cable production. Whether the surplus length control of OPGW cable fittings is reasonable directly determines the quality and service life of the cable. The remaining length of optical fiber should be controlled within a certain range to ensure a certain stretch window, which should not be too large. In the production process, it is necessary to understand the influence of various influencing factors on the remaining length of the optical cable, and think about the problems from different angles, so as to better control the quality of the optical cable, improve the product quality, and produce the optical cable with long service life and good quality.