EuroWire January 2017

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Technical article
January 2017 48
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
▲ ▲ Figure 1: Micro-duct with cable soaked in water
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.
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.
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).
Cable type Stranded loose tube structure
with G.652D fibres
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