WCA September 2021

Thermal retraction is mainly due to the crystallisation of the material, which is the process of rearranging the molecular structure. The crystallinity of PE and PBT during extrusion depends on the cooling rate. In the production and extrusion process, the cooling rate is related to the cooling water temperature, the extrusion speed of the extruder, and the length of the water tank. The ideal state is to perform segmental cooling, where the material is just extruded and cooled with warm water, and the water temperature is gradually lowered, and the traction speed is required. This is slow, and the sink is long. After the crystalline material is fully crystallised, heat shrinkage does not occur again. Thermal expansion and contraction are inherent properties of all materials. The cable sheath and casing are all plastic materials, and the coefficient of linear expansion is large – more than ten times that of metal materials. The loose tube material can be made of low-shrinkage PBT to minimise the change in retraction rate and thus reduce the elongation and retraction of the member. A reserved bend can be made during construction to cope with the effect of thermal expansion and contraction on the joint. Material stress occurs during the construction process and can be eliminated by effectively controlling the traction tension and the tension of the thread during the production process. During the construction process, the construction workers drag the cable and easily generate tensile stress on the outer sheath of the cable. When the cable is laid, the tensile stress is gradually released, causing the sheath to retract. This kind of stress can be used in engineering to park the cable after laying, so that the internal components of the cable can be stretched as much as possible under natural conditions, thereby reducing the influence of residual stress. 4 Cold-resistant cable performance tests We select 12 random fibres in the fibre optic cable to test the attenuation of fibre transmission wavelengths of 1,310nm and 1,550nm with OTDR under two large temperature-difference changes (-50°C ~ +70°C, and -60°C ~ +70°C). The temperature is cycled, and each point is tested at a constant temperature for 24 hours. The test results take the absolute value of the change. The specific results are shown in Table 3 . According to themethod F1 “Temperature Cycle” in the national standard GB/T 7424.2-2008, the test results show that the additional attenuation at 1,310nm and 1,550nm is lower than 0.01dB/km, which is better than the special requirements in YD/T 901-2018 for allowing additional attenuation of the fibre. 4.2 Environmental performance test analysis For the environmental performance and mechanical properties of the cable, for the bending performance of the cable at low temperature, we use the bending test according to the relevant provisions of GB/T 7424.2-2008. The results show that the test is carried out after freezing at -60°C for 24 hours. The diameter of the cable is bent 15 times. The result shows that the fibre inside the cable is not broken, and the ❍ Figure 3 : Cold- resistance cable With the previous design and analysis, we produced cold-resistant cables according to the above-mentioned cable structure design and material selection to perform the following performance tests. 4.1 Temperature performance test

outer sheath is not cracked. Other mechanical performance indicators are shown in Table 4 , and the results all meet the relevant indicators in YD/T 901-2018. 4.3 Test result analysis The cold-resistant optical cable uses low-temperature characteristic fibre gel and low-temperature resistant PBT material. Under the condition of fully satisfying the tensile performance in the cable-forming process, the fibre length in the casing is strictly controlled, and a suitable cable compression window is designed to ensure the temperature difference of the cable after the temperature difference. There is enough free space to avoid the increase in temperature additional loss due to the micro bend loss caused by the low temperature change of the fibre gel. The experimental results show that the additional loss caused by the temperature change of the optical fibre is less than 0.01dB/km, which effectively guarantees the normal operation of optical communication in alpine regions. The outer sheath of the cable is made of anti-cracking HDPE material, which avoids the breakage of the jacket under temperature ageing, thus ensuring the normal use of the cold-resistant cable and meeting the requirements of the normal operation of the communication network. 5 Conclusion This paper analyses various problems encountered in the practical application of cold-resistant optical cables in alpine regions, and summarises the relevant precautions of cold- resistant optical cables in the selection, design, production and construction of raw materials, which is the performance of optical fibre communication networks in an alpine environment. The protection has important significance, and it also has certain guidance for the construction of optical cable network lines and the prevention and maintenance of faults in other climate and topographic environments in China. 6 Acknowledgements The authors would like to express gratitude to everyone who cooperated in the completion of this paper and manufacture of the product. Thanks to our R&D engineering teams for designing, tracking and testing the samples. 7 References [1] Chen Bingyan: Design and manufacture of optic fiber and fiber optic cable [M]. Zhejiang University Press, 2016. [2] YD/T839.2-2014: Filling compounds and flooding compounds for telecommunication cable and optical fiber cable-part 2: Filling compounds for optical fiber. [3] YD/T1118.1-2001: Secondary coating materials used for optical fiber-part 1: Polybutylene terephthalate.

Courtesy of IWCS Cable & Connectivity Symposium, Charlotte, North Carolina, USA.

Hengtong Optic-Electric Co Ltd Suzhou, Jiangsu, China liuqing@htgd.com.cn www.htgd.com.cn

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Wire & Cable ASIA – September 2021