1、 INTERNATIONAL TELECOMMUNICATION UNION ITU-T L.57TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU (05/2003) SERIES L: CONSTRUCTION, INSTALLATION AND PROTECTION OF CABLES AND OTHER ELEMENTS OF OUTSIDE PLANT Air-assisted installation of optical fibre cables ITU-T Recommendation L.57 ITU-T Rec. L.57 (05
2、/2003) i ITU-T Recommendation L.57 Air-assisted installation of optical fibre cables Summary This Recommendation describes air-assisted methods for installation of optical fibres cables in ducts. These methods can be used to install micro cables into mini tubes, or jacketed cables into ducts or cond
3、uits. Installing conditions and equipment required shall be different in each case. Source ITU-T Recommendation L.57 (2003) was prepared by ITU-T Study Group 6 (2001-2004) and approved under the WTSA Resolution 1 procedure on 14 May 2003. ii ITU-T Rec. L.57 (05/2003) FOREWORD The International Telec
4、ommunication Union (ITU) is the United Nations specialized agency in the field of telecommunications. The ITU Telecommunication Standardization Sector (ITU-T) is a permanent organ of ITU. ITU-T is responsible for studying technical, operating and tariff questions and issuing Recommendations on them
5、with a view to standardizing telecommunications on a worldwide basis. The World Telecommunication Standardization Assembly (WTSA), which meets every four years, establishes the topics for study by the ITU-T study groups which, in turn, produce Recommendations on these topics. The approval of ITU-T R
6、ecommendations is covered by the procedure laid down in WTSA Resolution 1. In some areas of information technology which fall within ITU-Ts purview, the necessary standards are prepared on a collaborative basis with ISO and IEC. NOTE In this Recommendation, the expression “Administration“ is used fo
7、r conciseness to indicate both a telecommunication administration and a recognized operating agency. Compliance with this Recommendation is voluntary. However, the Recommendation may contain certain mandatory provisions (to ensure e.g. interoperability or applicability) and compliance with the Recom
8、mendation is achieved when all of these mandatory provisions are met. The words “shall“ or some other obligatory language such as “must“ and the negative equivalents are used to express requirements. The use of such words does not suggest that compliance with the Recommendation is required of any pa
9、rty. INTELLECTUAL PROPERTY RIGHTS ITU draws attention to the possibility that the practice or implementation of this Recommendation may involve the use of a claimed Intellectual Property Right. ITU takes no position concerning the evidence, validity or applicability of claimed Intellectual Property
10、Rights, whether asserted by ITU members or others outside of the Recommendation development process. As of the date of approval of this Recommendation, ITU had received notice of intellectual property, protected by patents, which may be required to implement this Recommendation. However, implementor
11、s are cautioned that this may not represent the latest information and are therefore strongly urged to consult the TSB patent database. ITU 2003 All rights reserved. No part of this publication may be reproduced, by any means whatsoever, without the prior written permission of ITU. ITU-T Rec. L.57 (
12、05/2003) iii CONTENTS Page 1 Introduction 1 2 References. 1 3 Installation of jacketed cables in ducts . 1 3.1 Considerations about elements when installing cable 1 3.2 Variants of air-assisted installation 2 3.3 Operations. 3 4 Installation of microcables in minitubes. 4 Appendix I Indian experienc
13、e: Installation of Optical Fibre Cables (OFC) by Air blowing method 5 ITU-T Rec. L.57 (05/2003) 1 ITU-T Recommendation L.57 Air-assisted installation of optical fibre cables 1 Introduction Air-assisted installation is based on forcing a continuous high-speed airflow along the cable with an air sourc
14、e. Moving air force pushes the cable and makes it advance forward at a typical speed supported by the equipment. Generally, the load on the cable is an order of magnitude lower than the typical force involved with other installation methods, like pulling techniques, reducing installation hazards. Ad
15、ditionally, with this technique, bends in duct run are not as important a matter of concern as they are in pulling techniques, so that installation speed increases and longer lengths of cable can be installed. Cables are installed without virtual stress, leaving the cable relaxed in the duct upon co
16、mpletion of the installation. There are several variants of installation: with/without a piston at the front end of the cable, or with a leaking piston. For variants without a piston, there is no pulling force at the front end of the cable: air flow exerts a distributed force along the entire cable.
17、 In addition, the connection to a pulling cord is not needed. 2 References The following ITU-T Recommendations and other references contain provisions which, through reference in this text, constitute provisions of this Recommendation. At the time of publication, the editions indicated were valid. A
18、ll Recommendations and other references are subject to revision; users of this Recommendation are therefore encouraged to investigate the possibility of applying the most recent edition of the Recommendations and other references listed below. A list of the currently valid ITU-T Recommendations is r
19、egularly published. The reference to a document within this Recommendation does not give it, as a stand-alone document, the status of a Recommendation. 1 ITU-T Recommendation L.1 (1988), Construction, installation and protection of telecommunication cables in public networks. 2 ITU-T Recommendation
20、L.10 (2002), Optical fibre cables for duct and tunnel applications. 3 ITU-T Recommendation L.12 (2000), Optical fibre joints. 4 ITU-T Recommendation L.35 (1998), Installation of optical fibre cables in the access network. 3 Installation of jacketed cables in ducts 3.1 Considerations about elements w
21、hen installing cable 3.1.1 Cable duct The combination of duct parameters and materials are critical in determining the installation requirements of specific cable designs when using air-assisted techniques (e.g., air tightness, circular shape, friction coefficient, wall thickness, etc.). Maximum duc
22、t diameter depends on the type of machine used. Inner duct diameter shall guarantee correct installation of cable. 2 ITU-T Rec. L.57 (05/2003) 3.1.2 Cable Maximum installation length is influenced by the stiffness and weight of the cable. A very flexible cable can only be pushed with a low pushing f
23、orce and it might be necessary to use an additional element at the front end of the cable, like an open shuttle, which allows the air stream to flow through its centre bore and exert a low pulling force at the front end of the cable. This element might also be necessary when the diameter of the cabl
24、e is very small compared with the internal diameter of the duct. When using a piston at the front end of the cable, a pulling force is exerted on the cable. In this case, maximum cable stress, which depends on the cable design, shall not be exceeded. Cable sheath friction coefficient and friction pr
25、operties of the duct liner (low enough) are critical. It should be as low as possible. It could be influenced by the selection of the cable coating and duct characteristics. If required, the use of the proper lubricant is an important factor to obtain an optimum performance. 3.1.3 Cable route Very t
26、ight bends in the route shall be avoided because maximum installation length depends on the number of bends, the location of them in the route, the shape and gradient of the cable route. Usually, the straighter the duct, the longer the installation length permitted. 3.1.4 Compressed air High-speed a
27、irflow that moves the cable into the duct is normally generated by a compressor on site. The maximum pressure of the compressor depends on the type of equipment used. Typically, it might be around 10-12 bar. Flow rate at the compressor output depends on the type of equipment and also on the internal
28、 diameter of the duct. Usually, the smaller the duct diameter, the lower the air flow rate and also the shorter the installation length, for a specific cable design. Compressed-air temperature has a great influence on the relevant parameters. At high temperatures, the material used in the cable jack
29、et and duct begins to soften. This increases the friction between cable and duct, causing a reduction in the system performance. For ambient temperatures exceeding 30 C, it is highly recommendable to use an air cooler inserted between the compressor and the blowing system. 3.1.5 Cable-insertion mach
30、ine A cable-insertion machine consists of a mechanical device that applies a force on the cable and controls its speed into the duct. It can be driven by an air or hydraulic motor with a manual and automatic run-stop dispositive. This element is divided into two construction principles: pushing of t
31、he cable by a rubber block caterpillar drive belt, and pushing by a notched wheel drive. 3.2 Variants of air-assisted installation The choice of method, described below, depends on several factors: type of cable (diameter, weight, stiffness), duct diameter, shape of the route (number of bends, locat
32、ion of the bends, gradient) and the equipment to be used. In the same manner, the installed lengths and laying speed depends on all these factors. 3.2.1 Installation method with a piston at the front end of the cable In this method, a piston is attached at the front end of the cable. It transfers a
33、defined pulling force to the cable which shall not exceed the allowed tensile load. The piston exerts only a fraction of the maximum permissible pulling force on the cable. If the piston gets to an oval section of the duct, it may get stuck in it. To avoid such a situation, the piston should have fl
34、exible cup sleeves or similar. ITU-T Rec. L.57 (05/2003) 3 It is also possible to use a piston with a smaller diameter than the internal ducts diameter applied at the front end of the cable (leaking piston). It could be an open shuttle, which allows the air stream through its centre bore. In this ca
35、se, leaking level shall affect the level of stress suffered by the cable. 3.2.2 Installation method without piston at the front end of the cable In this case, the cable is inserted into the duct free of pulling force by means of a large and fast flowing air volume. The air streaming through the duct
36、 exerts a certain thrust on the cable sheath: this force is caused by friction between air particles and cable sheath. The compressor needs to provide sufficient capacity of air for the installation. 3.3 Operations 3.3.1 Precautions When installing a cable using these methods, all precautions consid
37、ered in other installation methods (reels handling, cables, personal security, cable storage in splice point, etc.), need to be taken into account. Additionally, and previous to the installation of the cable, it shall be recommended: To plan the route, and determine the best locations where the blow
38、ing-in machines shall be placed, in order to achieve an optimum adaptation between the machine and the duct. This installation method allows the use of several blowing machines in series at different points of the same route, to obtain longer installation lengths or to solve complexity problems of t
39、he route. It may be possible to achieve installation lengths of 3 km, using only one blowing machine, depending on the characteristics of the route, the type of cable, duct and machine used. To check the continuity and integrity of the duct, in order to avoid losses of air pressure which may limit t
40、he performance of the system. In the points of discontinuity of the duct, it shall be necessary to splice the duct. To check the duct inside, in the direction of installation, in order to ensure the absence of obstruction elements inside the duct, like water, dust or even stones. In the same manner,
41、 the absence of any flattening in the complete length of the duct should be checked1. If required, a liquid lubricant can be added to the duct. To spread the lubricant uniformly along the duct, a sponge pushed by the air flow may be used. In some cases, the pouring of additional lubricant during the
42、 installation of the cable could be necessary. To clean the cable before inserting it into the cable-insertion machines. To take into account that a number of persons may be necessary in the installation process, in order that the following processes can be safely managed: handling the cable reel; h
43、andling the blowing machine; inserting the cable into the machine, and receiving the cable at the far end. When required, the cable may be installed from an intermediate point. In this case, once the first part of the cable has been installed, it is recommended to lay the remaining part of the cable
44、 as a figure of eight, or push it into a fleeting cage by means of the blowing-in machine. The maximum pressure the duct can support shall not be exceeded. _ 1There are different methods to check duct suitability (e.g., to blow in a sizing mandrel or a sponge). 4 ITU-T Rec. L.57 (05/2003) 3.3.2 Inst
45、allation process Once all precautions detailed in the previous paragraphs have been taken, and the blowing-in machines have been located in the right places, it is recommended: To prepare the front end of the cable. When using the installation method without piston, a light-weight cable guide shall
46、be fitted over the cable sheath to ease the movement of the cable around bends and through subduct connectors. When using the installation method with piston, the right cable grips shall be prepared: they will be attached at the front end of the cable To prepare the duct in order to adapt the blowin
47、g machine to the duct. If necessary, to fit the cable pushing elements of the blowing machine to the cable diameter. To put the cable into the insertion elements of the machine. To introduce the cable into the duct. To fix the cable to the insertion elements of the machine. To fix the duct to the bl
48、owing machine using an appropriate connector, in order to avoid air losses during the process. To start up the machine. The airflow generated by the compressor will begin dragging the cable inside the duct. At the distant end of the duct, the cable should be received. Care must be taken by operative
49、s because the cable may come out quite fast. If the installation process finishes at that point, a remaining length of cable, for cable splicing purposes, should be stored in the usual conditions. In case of several blowing machines being used in series, when the cable reaches the second installation point, it is necessary to stop the first machine and to introduce the cable into the second machine and duct, like previously detailed, and fix them to the cable. Afterwards, start up the first machine and then the second one. I
