EuroWire January 2017

Technical article

Investigating effects of freezing conditions on

micro-duct air-blown cables By Yunfang Ruan, Zhuang Xiong, Xiaoli Liu and Wenjing Ye, State Key Laboratory of Optical Fibre and Cable Manufacture Technology, Yangtze Optical Fibre and Cable Joint Stock Co Ltd, and Huawei Technologies Co Ltd, Shenzhen, Guangdong, China

Abstract In some cold areas, freezing conditions are a potential threat to micro-duct air-blown cables. In order to study the effects of freezing conditions on the transmission performance of optical fibres in micro- duct air-blown cables, two different experiments were designed and carried out in this paper. The test results reveal that both freezing in micro-ducts and that around end caps have insignificant influence on the transmission performance of the fibres and no visual physical damage to the cable has been detected after the experiments. 1 Introduction With the development of FTTx network construction, micro-duct air-blown cables are more frequently used due to the lack of duct resources, even in some cold regions. In this case, the water permeated into the micro-duct will be frozen under such low temperatures. Some concern such as the cable performance deterioration will discourage the wide application of micro-duct air-blown cables all over the world. In order to study the effects of freezing conditions on the transmission performance of optical fibres, freezing tests were designed to simulate the cold climate with the aid of a temperature cycling chamber. During the tests, the attenuation change of the fibres was monitored, and the appearance of the cable was checked. The test procedures are described in detail and the test results are carefully analysed.

Stranded loose tube structure with G.652D fibres

Cable type

Fibre count

96

Cable OD

6.1mm

Micro-duct type

HDPE

OD/ID of micro-duct

10/8mm

TCT cycles

2

▲ ▲ Table 1 : Common test conditions

2 Freezing test conditions

Two experiments were designed to simulate the conditions of water frozen in the micro-duct and around the end caps respectively with the aid of a temperature cycling chamber. The common test conditions in two experiments are shown in Table 1 . 3 Test for water frozen in micro-duct This experiment is designed to study the impact of freezing conditions on fibre attenuation while water is frozen in the micro-duct, and performed in accordance with IEC60794-1-22 Method F15: cable external freezing test. A 1.8km-long micro-duct air-blown cable and 80m-long micro-duct are used in this experiment. 3.1 Test procedures First, rewind the micro-duct onto a cable drum and blow the cable into the duct. Then, soak the 80m-long micro-duct (with cable inside) in a pool for 24 hours to make sure that the duct is completely filled with water, as shown in Figure 1 .

▲ ▲ Figure 1 : Micro-duct with cable soaked in water

After that, seal the duct with end caps before taking the cable drum out of the pool. Finally, put the cable drum into the temperature cycling chamber to perform the temperature cycling test. Before that, record the attenuation of each fibre at room temperature (23°C). 3.2 Temperature cycling programme The temperature cycling programme is set as follows (one cycle): 1 Lower the temperature from 23°C to 3°C within 30 minutes and hold this temperature for eight hours. 2 Then lower the temperature to -40°C within 30 minutes and hold it until the water is completely frozen and the ice temperature is -10°C or lower (by using a temperature monitoring device).

48

www.read-eurowire.com

January 2017