PD IEC/TR 62691:2011 pdf download – Optical fibre cables – Guide to the installation of optical fibre cables.
3.3 The potential for providing very long lengths of optical fibre cable can lead to the need for confidence that a particular installation operation will be successfully achieved, particularly in underground ducts, and a good indication can be provided, in some cases, by calculating the maximum cable tension. This maximum tension can be compared with the stated mechanical performance of the cable and, where these values are close, consideration can be given to methods for providing a greater margin of safety such as an alternative cable design, shortening the route, changing the route or direction of cabling, provision of intermediate winches, or by taking special precautions at particular locations. Calculation considerations are indicated in the clauses which follow. Cable tensions in overhead installations where the cable is lashed or clipped to a messenger strand or other supporting members are generally minimal. Rollers or similar types of hangers are used to support the cable at frequent intervals such that it does not sag during the installation process. Rollers, quadrant blocks, or other guides should be used when the cable line changes direction in order to minimize cable tensions and support the cable’s minimum bend radius. If cables are pulled from the end, many of the same considerations for pulling into ducts are present, though generally with lower tensions. Changes in elevation may increase the tension, and must be considered. Moving reel installation methods generally exhibit minimal cable tension, but jerking of the cable due to reel inertia and movements must be guarded against. See the further discussion in 4.5. Considerations for self-supporting cables (figure-8 or ADSS, for example) are addressed in 4.5. Cable tensions in ploughing or trenching are generally minimal, much smaller than the rated tension of the cable. Momentary tensions and jerking due to cable reel inertia when paying off cables, which result in tensions in the immediate area being installed, should be considered.
Two sets of equation are presented below. The first, presented in 3.5.2, is used to calculate cable tension in pulling applications. The second, presented in 3.5.3, is used to calculate cable tension in cable pushing and blowing applications; it may also be used for pulling. Note that the first set, for pulling only, is much simpler and neglects cable weight in Equation 3. The second equation, for any of the duct installation methods, comprises very complex equations involving much more data, including amplitude and frequency of innerduct undulations. Much of this sort of data are generally not known and must be estimated from cable experiments and empirical data from similar installations. Maximum cable tension 3.5 General 3.5.1 The following main contributory functions need to be considered when calculating cable tensions: – the mass per unit length of cable; – the diameter of the cable; – the stiffness of the cable; – the coefficient of friction between cable sheath and surfaces with which it will come in contact; – the inner diameter of the duct; – deviations (bends and undulations) and inclinations. Total cable tension – pulling applications
The COF between cable and duct is 0,1 , the (right-angled) bends in the trajectory are of radius of 1 ,2 m and the straight sections still make undulations with amplitude of 5 cm and period of 8 m. IEC/TR 62470 describes techniques to measure the coefficient of friction (COF) between cables and ducts. Pulling force: The pulling force is calculated for the situation that the winch is placed at the beginning of the trajectory. The cable is placed somewhere in the field. First the pulling force is calculated for one location of the cable, at 1 1 00 m, with boundary condition that the cable enters the duct without any tension as shown in Table 2.