Author: Yongfeng Yang/ Yi Xu/ Xing Zheng /Junyi Zhou /Wentao Ni/Shuaifeng Lu From Quzhou Power supply company of state grid Zhejiang electric power co.,ltd./Nantong saibo communication co., ltd.
Ⅰ. Preface
In the fiber optic cable line, the investment in cable splice box does not exceed 1%, while the failure rate of the line caused by splice box can be more than 70%, mainly due to the additional attenuation of the fiber in the box after a period of operation and broken fiber. For outdoor cable lines, these failures include water seepage, air leakage and ant damage caused by premature ageing of the box and seal failure due to poor box materials, structural design and jointing and installation processes, as well as the reduction in bending radius due to disorderly changes in the state of the optical fibers in the box after operation of the splice box, resulting in greater additional attenuation or fiber breakage due to stress.
The cable splice box is a sealed unit, consisting of an outer casing, seals, fiber storage tray and fiber connectors. If the outer casing of the box is not obvious aging, cracking and other phenomena, the above faults are difficult to be directly detected in time, especially in the splice box after the operation of the random disorderly changes in the state of the fiber tray.
A large number of operational practices have shown that even after a period of operation, even with a reasonably designed and good quality splice box, with the correct splicing technology and compliant construction and assembly, the state of the optical fiber tray can still change to a greater or lesser extent, and in some cases very seriously, even to the point of communication failure.
In order to detect such potential hidden problems as early as possible, the line maintenance unit usually develops a manual inspection system, regularly or irregularly open the splice box for inspection, with a view to early detection and timely disposal.
Opening the box for disposal includes reorganising the fiber and sometimes re-fusing the fiber, and replacing the sealing elements after the box has been opened and the original seal has been broken. Not all splice boxes need to be opened and re-coiled and fused, but as the box can only be opened to see the state of the internal fiber tray, this results in a lot of duplication of effort and long inspection cycles, high costs and high work intensity, but still low efficiency.
The cable splice box is a sealed unit, consisting of an outer casing, seals, fiber storage tray and fiber connectors. If the outer casing of the box is not obvious aging, cracking and other phenomena, the above faults are difficult to be directly detected in time, especially in the splice box after the operation of the random disorderly changes in the state of the fiber tray.
A large number of operational practices have shown that even after a period of operation, even with a reasonably designed and good quality splice box, with the correct splicing technology and compliant construction and assembly, the state of the optical fiber tray can still change to a greater or lesser extent, and in some cases very seriously, even to the point of communication failure.
In order to detect such potential hidden problems as early as possible, the line maintenance unit usually develops a manual inspection system, regularly or irregularly open the splice box for inspection, with a view to early detection and timely disposal.
Opening the box for disposal includes reorganising the fiber and sometimes re-fusing the fiber, and replacing the sealing elements after the box has been opened and the original seal has been broken. Not all splice boxes need to be opened and re-coiled and fused, but as the box can only be opened to see the state of the internal fiber tray, this results in a lot of duplication of effort and long inspection cycles, high costs and high work intensity, but still low efficiency.
Ⅱ. The Internal Fiber Change and Analysis
1. A brief analysis of the causes of fiber retraction
In order to avoid the impact of external or external forces on the fiber optic cable and to provide protection for the relatively fragile fiber, the fiber needs to have a certain redundant length within the cable (called "fiber residual length"). Therefore, outdoor fiber optic cables are generally loosely constructed, i.e. the optical units are loosely sheathed to provide the primary residual length, the optical units are stranded to provide the secondary residual length, and then covered with a comprehensive jacket (e.g. containing steel wire, steel or aluminium tape) depending on the environmental requirements. The primary residual length and the secondary residual length together form the "integrated residual length" of the fiber optic cable, which is "stored" within the cable in the bent state of the fiber.
It can be seen that the length of the fiber within the cable (known as the "fiber length") is not the same as the length of the cable (known as the "skin length"), the fiber length must be reasonably greater than the skin length and the fiber within the cable is loose and displaceableable. This is the basic principle and working principle of the design and manufacture of loose-structured outdoor fiber optic cables.
In order to seal the end of the cable, the splice box clamps the outer sheath of the cable and does not control the remaining length of the fiber in the cable and its specific form. When the length of the cable changes due to temperature changes, or by the construction of the inevitable external forces such as pulling, bending, twisting, plus the outer sheath in the cable formation process will be released over time and the length of the increase (can be called "creep elongation"). Therefore, the "retraction" of the optical unit or fiber is essentially the "elongation" of the outer sheath, which results in a relative reduction in the length of the fiber in the splice box. The bend radius of the fiber on the storage tray is then reduced and, in severe cases, the fiber is "straightened".
If the bend radius of the fiber in the storage tray is still within the permitted range, the additional attenuation does not increase significantly. If the bend radius is less than the permissible value or even straightened, the account may still not show a significant increase in additional attenuation with a conventional OTDR, but by this time the fiber has already developed a large strain (stress) and is already on the eve of fracture when significant additional attenuation is observed.
In a sense, therefore, the change in the state of optical fiber coiling that occurs after the operation of a splice box is inevitable and is not an isolated phenomenon but a common "normal" phenomenon, only the state of change varies and the degree of impact on communication reliability varies. However, as the splice box is a sealed body, this phenomenon can only be observed with the naked eye when the box is opened.
Ⅲ. Fiber Optic Cable Splice Box for Pipe Corridor
1. Basic requirements of outdoor cable splice box
Mechanical properties include: tensile, flattening, impact, bending, twisting, dropping, axial compression; environmental properties include: temperature cycling, low temperature shock, continuous high temperature, vibration, solar radiation, chemical corrosion; electrical properties include: insulation resistance, voltage strength.
It can be seen that the length of the fiber within the cable (known as the "fiber length") is not the same as the length of the cable (known as the "skin length"), the fiber length must be reasonably greater than the skin length and the fiber within the cable is loose and displaceableable. This is the basic principle and working principle of the design and manufacture of loose-structured outdoor fiber optic cables.
In order to seal the end of the cable, the splice box clamps the outer sheath of the cable and does not control the remaining length of the fiber in the cable and its specific form. When the length of the cable changes due to temperature changes, or by the construction of the inevitable external forces such as pulling, bending, twisting, plus the outer sheath in the cable formation process will be released over time and the length of the increase (can be called "creep elongation"). Therefore, the "retraction" of the optical unit or fiber is essentially the "elongation" of the outer sheath, which results in a relative reduction in the length of the fiber in the splice box. The bend radius of the fiber on the storage tray is then reduced and, in severe cases, the fiber is "straightened".
If the bend radius of the fiber in the storage tray is still within the permitted range, the additional attenuation does not increase significantly. If the bend radius is less than the permissible value or even straightened, the account may still not show a significant increase in additional attenuation with a conventional OTDR, but by this time the fiber has already developed a large strain (stress) and is already on the eve of fracture when significant additional attenuation is observed.
In a sense, therefore, the change in the state of optical fiber coiling that occurs after the operation of a splice box is inevitable and is not an isolated phenomenon but a common "normal" phenomenon, only the state of change varies and the degree of impact on communication reliability varies. However, as the splice box is a sealed body, this phenomenon can only be observed with the naked eye when the box is opened.
Ⅲ. Fiber Optic Cable Splice Box for Pipe Corridor
1. Basic requirements of outdoor cable splice box
Mechanical properties include: tensile, flattening, impact, bending, twisting, dropping, axial compression; environmental properties include: temperature cycling, low temperature shock, continuous high temperature, vibration, solar radiation, chemical corrosion; electrical properties include: insulation resistance, voltage strength.
Outdoor cable connector box appearance is mainly divided into two types of horizontal and vertical as shown in Figure 1.
Figure 1 two typical outdoor fibre optic cable splice boxes
Figure 1 (a) shows a 4-port (can be "two-in, two-out" or "one-in, three-out") horizontal splice box, the shell of which is usually made of engineering plastic to half open type (also known as "Haff The housing is usually made of engineering plastic in a half-open type, consisting mainly of two symmetrical sized top and bottom covers with sealing elements, as well as the internal components for fixing the optical cable. The 4-port box is mainly used for the branching or distribution of multiple cables, even if two cables are docked separately (two in and two out), they share a common storage tray system and do not have independent functions.
The multi-port vertical splice box shown in Figure 1 (b) is also known as a dome closure, whose housing material can be engineering plastic or aluminium alloy, stainless steel, etc. The internal structure and function is similar to that of a horizontal one.
The optical performance of the splice box depends mainly on the internal components, the fiber optic splice components and the manner and condition of the fiber tray. Other properties depend mainly on the outer casing, sealing components and the installation process and related technology.
2. Requirements for the cable splice box for pipe corridors
Corridor, as the name implies, is a corridor for laying pipes, initially mainly refers to chemical plants in the air or underground concentrated deployment of various pipeline clusters. Optical cable corridor generally refers to the use of shallow buried or trench way of construction, with openable cover but its internal space can not meet the normal passage requirements of personnel, for the accommodation of power cables and communication cables (including optical fiber cable) facilities, but also includes the channel, tunnel or culvert. An urban integrated pipe corridor is a tunnel space under the city that is accessible to staff, where all types of engineering pipelines such as power, communication (including fiber optic cables), heat and water supply are integrated, with above-ground attachments for outlets and vents and other facilities. The integrated pipeline corridor is mainly divided into trunk line integrated pipeline corridor, branch line integrated pipeline corridor and optical cable line corridor.
The industry standard "YD/T-814.1" divides the application occasions of the splice box into three categories: overhead, pipeline (tunnel) and direct burial (there is no classification for the application of the corridor), and divides the optical cable connection into two categories: straight and divergent.
The main characteristics of the corridor can be seen: on the premise of meeting the requirements of YD/T-814.1, the structure of the splice box for the corridor should be horizontal, and in order to improve the flexibility of the network, it should be multi-port, preferably with multiple independent cable channels.
It should be said that the working environment and conditions of the splice box in the corridor are relatively better than in direct field applications, but the high degree of cable integration places higher requirements on the maintenance of optical cables, especially for the fiber change inside the box after the operation. Yet currently cable splice boxes are still opened and inspected one by one, and the re-sealed regardless of whether or not there are faults, which is undoubtedly intensive, costly and still inefficient.
The multi-port vertical splice box shown in Figure 1 (b) is also known as a dome closure, whose housing material can be engineering plastic or aluminium alloy, stainless steel, etc. The internal structure and function is similar to that of a horizontal one.
The optical performance of the splice box depends mainly on the internal components, the fiber optic splice components and the manner and condition of the fiber tray. Other properties depend mainly on the outer casing, sealing components and the installation process and related technology.
2. Requirements for the cable splice box for pipe corridors
Corridor, as the name implies, is a corridor for laying pipes, initially mainly refers to chemical plants in the air or underground concentrated deployment of various pipeline clusters. Optical cable corridor generally refers to the use of shallow buried or trench way of construction, with openable cover but its internal space can not meet the normal passage requirements of personnel, for the accommodation of power cables and communication cables (including optical fiber cable) facilities, but also includes the channel, tunnel or culvert. An urban integrated pipe corridor is a tunnel space under the city that is accessible to staff, where all types of engineering pipelines such as power, communication (including fiber optic cables), heat and water supply are integrated, with above-ground attachments for outlets and vents and other facilities. The integrated pipeline corridor is mainly divided into trunk line integrated pipeline corridor, branch line integrated pipeline corridor and optical cable line corridor.
The industry standard "YD/T-814.1" divides the application occasions of the splice box into three categories: overhead, pipeline (tunnel) and direct burial (there is no classification for the application of the corridor), and divides the optical cable connection into two categories: straight and divergent.
The main characteristics of the corridor can be seen: on the premise of meeting the requirements of YD/T-814.1, the structure of the splice box for the corridor should be horizontal, and in order to improve the flexibility of the network, it should be multi-port, preferably with multiple independent cable channels.
It should be said that the working environment and conditions of the splice box in the corridor are relatively better than in direct field applications, but the high degree of cable integration places higher requirements on the maintenance of optical cables, especially for the fiber change inside the box after the operation. Yet currently cable splice boxes are still opened and inspected one by one, and the re-sealed regardless of whether or not there are faults, which is undoubtedly intensive, costly and still inefficient.
Main Features of the Corridor Type Splice Box:
A horizontal half-opening appearance, but with an asymmetrical housing structure;
The optical cable ports and internal structure are all housed in the cassette;
The viewable window is made of a mechanically strong account-transparent material and is sealed with the cassette holder, seals and compression frame (usually not opened unless a coiled fiber or fusion connection has to be handled);
The top cover is a solar radiation, dust and dirt-proof cover with a certain mechanical strength, resistant to impact and crushing, which can be opened repeatedly in a simple way to visually check the status of the tray fiber through the viewable window
The optical cable port has properties such as resistance to bending, twisting and axial compression in addition to sealing.
A reasonable coiled fiber unit with excellent optical and vibration resistance properties.
All cosmetic, optical, sealing, re-encapsulation, water immersion, mechanical, environmental, electrical and environmental properties can be met.
The optical cable ports and internal structure are all housed in the cassette;
The viewable window is made of a mechanically strong account-transparent material and is sealed with the cassette holder, seals and compression frame (usually not opened unless a coiled fiber or fusion connection has to be handled);
The top cover is a solar radiation, dust and dirt-proof cover with a certain mechanical strength, resistant to impact and crushing, which can be opened repeatedly in a simple way to visually check the status of the tray fiber through the viewable window
The optical cable port has properties such as resistance to bending, twisting and axial compression in addition to sealing.
A reasonable coiled fiber unit with excellent optical and vibration resistance properties.
All cosmetic, optical, sealing, re-encapsulation, water immersion, mechanical, environmental, electrical and environmental properties can be met.
IV. Summary
Fibre optic cables must have a reasonable residual length of fibre, which is stored in the bent state of the fibre in the loose tube and stranded pitch of the cable. During the processing, construction and working life of a fibre optic cable, the residual length of the fibre optic cable is always changing, i.e. the form of the fibre in the tube is not constant, it is always within a certain range of "self-adjustment", thus cushioning the impact of external forces.
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