Cable in Duct Installation: Lubrication Makes the Difference

Transcription

1 Cable in Duct Installation: Lubrication Makes the Difference Willem Griffioen Plumettaz SA Bex, Switzerland Abstract Not only jetting technology has contributed to enhanced cable-induct installation performance, also development of new lubricants (optimized for jetting) has played a major role, leading to lengths up to 3.7 km for a single blow. Quality of lubricant and the right way of application are key factors. In this paper it is described how and how not to apply lubricants in (micro)ducts. Also a family of cable lubricators is presented. Some examples are given of how these ways of lubrication benefit jetting installation. Keywords: Cable; duct; microduct; blowing; jetting; lubricant; lubrication; cable lubricator. 1. Introduction Telecommunications cables have been installed in ducts for many years now. Traditionally they were installed by winch pulling. Today installation by jetting [1,2], a synergy of blowing [3] and pushing, has become the standard. This technique has made it possible to increase installation lengths considerably, allowing installing long cable lengths without splice, an important benefit for optical cables. Not only the jetting technology has contributed to enhanced installation performance, also the development of new lubricants (optimized for jetting) has played a major role. While in 1987 for the first jetted cables the intermediate assist length increased from 175 m for pulling to 700 m for jetting (still using paraffine oil), today single jetting lengths up to 3.7 km (with today s lubricant) have been reported [4,5], moreover reached with much higher filling degrees (ratio cable diameter - duct inner diameter). Using good lubricants makes the difference. Application of the lubricant is also important. Traditionally lubrication was done by feeding the cable through a box with lubricant saturated foam material. For jetting this was not convenient, because a) it made the drive wheels or belts slip and b) most of the lubricant was wiped and blown off when the cable was entering the pressure chamber. During the early days of jetting, paraffine oil was poured into the duct, which was then spread over the duct by the airflow. Later, a more reliable way of application was used, by blowing a foam pig immediately after the lubricant. For microducts it was found that lubrication is more critical than for standard ducts. Measurements of the coefficient of friction on samples taken out of the field showed that only the first length is lubricated well. When using larger quantities of lubricant, there is a risk that too much lubricant remains in the microduct, acting as a viscous brake on the cable. Using larger foam plugs helped, but they often got stuck in the microduct. The right dimensions and material for the foam shall be used. Still then, microducts with an inner diameter smaller than 5 mm cannot be lubricated well in a practical way. For this reason the cable lubricator was developed. It looks like the old method: the cable is fed through a lubricant saturated foam material. But, this foam material is placed inside the pressurized space, the airflow is bypassed around it and cable guiding avoids buckling. It was found to increase jetting length surprisingly much, even for perfectly lubricated microduct. For the smallest cables (around 2 mm diameter) a factor of up to 10 in jetting length (depending on air humidity) was achieved, probably caused by reduction of static electric charging of the cable. In this paper a study of different ways of lubrication is presented. The effects on jetting length will be given. Also a complete family of cable lubricators will be introduced, suitable for the smallest microducts to the largest ducts, with and without lubricant reservoir, dividable or not and for building into jetting equipment or placing in-line with the duct. 2. Lubrication 2.1 Theory In most cases lubricants are used to reduce the friction between cable and duct. Two different types of friction can be distinguished: hydrodynamic friction and boundary friction [6]. Hydrodynamic or "thick-film friction" is significant on lowtension sections of the ducts, which is usually the case with jetting. Under these conditions, the cable actually floats on a thick film of lubricant. The viscosity of the lubricant plays an important role for the hydrodynamic friction, and it is preferable to have a low-viscosity lubricant and applying an as thin as possible layer to minimize this type of friction. Another way to minimize this friction is to enlarge the "effective distance" between cable and duct by using grooves in the cable and/or duct (the excess amount of lubricant can then be squeezed into the grooves). The hydrodynamic friction increases with pulling speed of the cable and will hence always be significant at very high pulling speeds. When the normal pressure between cable and duct is high, or when the thick-film friction is minimized sufficiently, the boundary or "thin film" friction becomes significant. These conditions exist in high-tension sections and bends of the duct. Under high sidewall bearing pressure, lubricants get squeezed into a thin film and many break down and lose effectiveness. Lubricants need to be optimized for both types of friction. As stated before, when using the jetting technique, where the normal forces are kept relatively low, it is especially important to minimize the hydrodynamic friction. Lubricants need not only be optimized for initial friction coefficient. They should remain their properties during the pull and, e.g., not dry over time. Lubricants should also remain their properties over a longer time when the possibility to remove the cable in a later stage is wished, or when the ducts are prelubricated. Combinations of cable, duct, lubricant and a possible fourth material, e.g. water, should be well tested in this case. The lubricant may, in general, never have an aggressive character and should be compatible with duct and cable. Lubricants should next be easily to spread, and remain spread, through the duct and/or along the cable. Finally, with the jetting technique, lubricants should not foam in the duct. It might be clear from the preceding that the choice of a good lubricant must be accompanied by tests. 54

2 Lubrication not only reduces the coefficient of friction between cable and (micro)duct, it often also reduces static electric charging of the cable. Electric charging of the cable is a well known phenomenon for the smaller cables (order of 1 mm diameter) used for FttH, where it becomes a dominant limiting factor. It has been found that lubrication of such a cable can improve the jetting distance by an order of magnitude! 2.2 Duct Lubrication Lubricant can be applied either on the cable or on the duct wall. In the latter case usually an amount of lubricant is poured into the duct and the lubricant is spread by blowing a foam sponge through. Lubrication of ducts is especially critical for microducts, with an inner diameter typically less than 13 mm. Here it is difficult to spread the lubricant over the entire length of the microduct. For this MicroJetting Lube, a special jetting lubricant (concentrated lubrication agents, low viscosity), was developed. The difficulty of microduct lubrication is illustrated by some test results on 7/5.5 mm HDPE microducts. In Figure 1 measured coefficients of friction (COFs) are shown from field lubricated samples, small lengths of microduct cut out and tested by a wheeltest [7,8] (radius 28 cm over 360º, 3.8 mm cable, counter mass 206 g). Field lubrication was done over 1500 m by pouring in 24 ml (1 m of microduct filled) of lubricant (still experimenting with composition) and distributing it by blowing a foam sponge ( 12 mm, 42 mm long) through. Clearly the lubricant was not spread well. Jetting the cable was only possible over a few hundred meters. When the cable was pulled out it was dripping with lubricant, another proof for bad spreading. COF x (m) Figure 1. Measured coefficient of friction (COF) from field lubricated samples of 7/5.5 mm microducts (still experimenting with lubricant) After the special lubricant for microducts was developed, first also the foam sponge was enlarged, to 20 mm and 80 mm long for the 7/5.5 mm microduct, in order to reach the maximum possible jetting length of 2500 m (at that time), needed for the CERN project [4]. It was found that the large foam sponge pushed all the lubricant in front of it and really spread it well, as a very thin layer. But, after long lengths, when all lubricant was used, the foam sponge ran dry and got stuck. To avoid this, an excess amount of lubricant was used (40 ml every 500 m). Blowing the foam sponge through took about 10 minutes per 500 m, caused by the viscosity of the column of lubricant (a second and third foam sponge took only 3 minutes per 500 m). At the end the excess amount of lubricant was pushed out. In this way many lengths of 2500 m cable (today s record 3.7 km, with cable lubricator with lubricant reservoir, see further) were jetted in, all of them in one blow. Sometimes little less large foam sponges were used. In that case the lubricant was not spread fully, recognized by a drop in cable speed in the beginning. But, the cable itself also spreads the lubricant a bit, and the total length was still reached. In practical field installation it is not always as easy as at CERN, where the microducts could be reached at all places and the conditions were clear (constant temperature around 20 C, compressor pressure of 16 bar). In an installation in Sweden, where also a long length (not accessible halfway) needed to be bridged, the conditions made the CERN lubrication procedure difficult to use. Not only the low temperature (around freezing) caused the viscosity of the lubricant to increase, also the compressor could only reach 6 bar. Moreover, all the lubricant had to be poured in at the injection side. Lubrication (and after that the cable installation) was successful, but blowing the sponge through took hours! Today smaller foam sponges are used again (except for special projects requiring the maximum achievable) and smaller quantities of lubricant. The lubrication of the microduct is now an acceptable procedure, as long as microduct inner diameters are not smaller than 5 mm. With MicroJetting Lube still perfect jetting results are obtained, especially when also using a cable lubricator (see further). The following rule of thumb is recommended for the quantity of lubricant (all poured in at the injection side): quantity (ml / 1000 m) = 2 x ID (in mm). The recommended sizes of the foam sponges (of the right material) are given in Table 1. Table 1. Sizes of foam sponges to lubricate microducts Microduct ID (mm) Length (mm) 5-7 mm mm mm mm Cable Lubrication Besides lubricating the (micro)duct, it is also possible to lubricate the cable, using a cable lubricator [9] (or doing both). Lubricating the cable before entering the jetting device is one possibility, but a few drawbacks must be considered then: The lubricated cable might slip between the drive belts or the wheels of the jetting device. Part of the jetting liquid is wiped and blown off when the cable enters the pressure chamber of the jetting device. It has been found in practice that lubricating the cable is much more effective when this lubrication is done after the jetting equipment. Because the cable has already been injected into the pressure zone, the cable lubricator must be able to handle this, which means that: 1. The cable lubricator shall have minimal leakage of the air, at least much less than what can be transported through its flow channel (especially important for dividable cable lubricators) 2. The cable lubricator must be able to bypass the airflow needed for jetting without noticeable pressure drop (large enough flow channel) 3. The cable lubricant reservoir (when present) must be able to handle pressure variations without premature discharge of the lubricant 55

3 At the same time care shall be taken that: 4. The cable is guided such that the pushing force of the jetting equipment is not causing buckling of the cable 5. The lubricant is applied in a continuous but thin layer, without causing too much friction for the cable when passing the cable lubricator The following cable lubricator constructions can be distinguished: a. Dividable or non-dividable b. Built in jetting device c. Coupled in-line with duct d. Without lubricant reservoir e. With lubricant reservoir Different cable lubricators have been produced and used now. It has been found that consumption of lubricant is much less than for lubrication of the microduct. The rule of thumb to estimate the required quantity of lubricant to lubricate the cable (with the lubricators described in this paper) is: quantity (ml / 1000 m) = 0.2 x cable diameter (in mm). But, every time the lubricator is opened, a few ml extra lubricant might be needed to soak the foam sponge again. Also the lubricant is much easier to apply for cable lubrication: just insert the cable lubricator in your jetting machine or duct. This advantage is especially important for small microducts, where duct lubrication is more critical and requires more time. For microducts with diameter smaller than 5 mm it is recommended even not to lubricate the microducts at all. When combining lubrication of microduct and cable, the longest jetting lengths have been reached. This is shown in Section 4 about experiences with lubrication. 3. Design of Cable Lubricators Three sizes (and types) of cable lubricators are presented. The smallest one is a non-dividable one and does not have a lubricant reservoir. It is simply coupled in-line with the duct, just after the jetting equipment. It works perfectly with small FttH cables, where no tandem jetting is needed to connect the relatively nearby homes. The medium size cable lubricator is dividable and is equipped with a lubricant reservoir. It is built inside the jetting equipment. Tandem jetting is possible with this cable lubricator. The large size cable lubricator is also dividable and contains a lubricant reservoir. This one can again be simply coupled in line with the duct. Tandem jetting is again also possible, except for the option of jetting bundles of microducts. 3.1 Small Size Cable Lubricator Figure 2. Small cable lubricator, in-line with microduct. Figure 3. Small cable lubricator, with UltimaZ. The small size cable lubricator, see Figure 2 and 3, can be used to lubricate cables with diameters ranging from 0.8 mm to 4 mm and for microducts ranging from 3/2 mm to 12/9.6 mm. It contains foam sponges that are soaked wet with lubricant. The use is easy. First the foam sponges are punched through with a needle, which can be done with the lubricator closed. Then the cable is pushed through and the lubricator is simply snapped on (between) the microduct. It is intended to be used for single drop installations, e.g. for connecting homes in FttH networks. 3.2 Medium Size Cable Lubricator Figure 4. Medium cable lubricator for building into jetting equipment. Dividable and contains reservoir. The medium size cable lubricator, see Figure 4, can be used to lubricate cables with diameters ranging from 1 mm to 9 mm and for microducts ranging from 4/3 mm to 16/13 mm. It contains a lubricant reservoir and foam sponges to wipe a thin layer of lubricant on the cable surface. The lubricator is dividable and is built into the jetting equipment (MicroJet, MiniJet and CableJet). For the smaller cables a guiding insert, see Figure 4 on the left, is extending into the jetting equipment to prevent buckling of the cable. The construction is such that the airflow that can be transported to the lubricator amply compensates for the air leak between the 2 halves. This lubricator can be used for tandem jetting operation. In Figures 5 and 6 the lubricator is shown built in a MicroJet and CableJet, respectively. 56

4 Figure 7. Large cable lubricator, in-line with duct. Dividable and contains reservoir. Figure 5. Medium size cable lubricator built into MicroJet. Figure 6. Medium cable lubricator built into MiniJet. 3.3 Large Size Cable Lubricator Figure 8. Large cable lubricator, with CableJet (top) and SuperJet (bottom). The large size cable lubricator, see Figure 7 and 8, can be used to lubricate cables with diameters ranging from 4 mm to 18 mm and for (micro)ducts ranging from 12/9.6 mm to 50/40 mm (for the latter size an adaptor piece is used). It also contains a lubricant reservoir and foam sponges to wipe a thin layer of lubricant on the cable surface. This lubricator is also dividable, now not built into the jetting equipment, but placed in-line with the duct, like for the small size cable lubricator. The ducts that are used with this cable lubricator are such large that they allow passing of sufficient airflow to compensate for the air leak between the 2 halves of the lubricator. This lubricator combines the option of tandem jetting operation with simple duct coupling technique. There is also an option to lubricate bundles of microducts (or cables), but here the lubricant applying chamber is not dividable. As microducts are always installed not in tandem (they are easy to couple to longer lengths) this is not a problem. 4. Experiences with Lubrication Large scale and documented experience with cable lubrication has until now only been gained with cables with diameters ranging from 1.3 to 9 mm. In Table 2 an indication of the jetting performance, in %, has been given for different combinations of microduct and cable lubrication [10]. For microducts also low friction liners (solid liner or pre-lubricated) have been included. The maximum value of 100% is typically a jetting length of 1500 m, reached with 6-8 bar in a trajectory with 180 bends every 100 m, according to IEC specification [11]. In Table 2 also an indication of the coefficient of friction (COF), calculated using JetPlanner [2,3], is given between parentheses. 57

5 Table 2. Jetting performance (%) and COF (between parentheses) for different ways of lubricating microduct and cable Microduct \ Cable No lubrication Cable Lubricator No lubrication 10-30%(0.2-1) 50-70%( ) Liner or pre-lub 50-70%( ) 70-90%( ) Field lubrication 60-80%( ) 100%( ) Table 3. Jetting performance (m) and COF (between parentheses) for different 7 mm microducts and ways of lubricating No lub Duct lubed Cable lubed Both lubed 173(0.4) 1372(0.08) 1515(0.065) * 360(0.23) 1120(0.09) 1257(0.08) 170(0.4) 952(0.10) 1140(0.085) 135(0.5) 1060(0.09) 1144(0.085) 990(0.12)** 1100(0.10)** A few examples of field tests, with results that are used to construct Table 2, will now be given. The 1.8 mm FttH cables, as described in [12], have been tested in a trajectory of 1000 m of 4 mm HDPE duct with 180 bends every 100 m, according to IEC specification [11]. The microduct was not lubricated. The cable was then jetted in with 10 bar, but could not reach further than 150 m. When using the small size cable lubricator, a length of 1000 m could be reached. When using a lubricator with lubricant reservoir (first version, still non-dividable, not described here) a length of 1500 m was reached. This represents the lowest (10%) number, up-left in Table 2. Reduction of the coefficient of friction alone is not able to explain this large effect of the cable lubricator. Static electric charging is probably the cause for the bad jetting result when not using the cable lubricator. It could be recognized by shocks (stop and go) in the installation of the cable (this effect was not found with the larger cables). This effect could be postponed by selecting a lower cable speed (installation started at 40 m/min, at 20 m/min the final 150 m was reached), probably because the static electric charging depends on the cable speed. Static electric charging is depending on the conditions of the air, temperature and, more important, relative humidity. No record was made of the air humidity in the above test. But, there was also no need to do this, because no dependence of cable jetting performance was found in the thousands of kilometers of this 1.8 mm cable installed in practice (with lubricator). In later tests even smaller, 1.3 mm, cables were tested. Here tests were done in air with optimized conditions and in air directly from the compressor with after cooler (too dry on the 20 C day). The differences in performance for the 2 conditions were large when not using a cable lubricator, comparable to the difference described in the above test. Also the same shocks were clearly present. When using the cable lubricator, the result of the optimized air conditions could be copied with the too dry air. Also larger cables have been extensively tested with the cable lubricator. For example, in different HDPE 7/5.5 mm microducts (different types and different manufacturers), cables with diameter of 3.9 mm were jetted in. In Table 3 the jetting lengths reached (end speed 20 m/min, when not indicated differently) have been summarized. Also the coefficient of friction (COF), calculated using JetPlanner [2,3], has been given between parentheses. Jetting was done with 10 bar (when not mentioned differently) with the microducts laid in loops with 180 bends every 125 m, according to IEC specification [11], and open at around 1500 m. 275(0.27)*** 683(0.13) 1177(0.09)*** 1275(0.09) 230(0.35) 1182(0.09) 1400(0.075) 1173(0.09)*** 1440(0.075) 1133(0.09) 52(>1) 765(0.12) 947(0.10) 102(1) 536(0.16) 320(0.25) 1315(0.08) *68 m/min **12 bar ***pre-lubed Graphical representation Jetting length (m) Only duct lubed Only duct prelubed Only cable lubed Both lubed Another advantage of lubricating the cable is that it can be done at freezing temperatures. Simply store the cable lubricator and the bottles of lubricant at a non-freezing place (e.g. a car). Jetting the cable can then be done without freezing problems, except that for long installations a hairdryer might be needed to keep the cable lubricator frost free. The thin layer applied on the cable might freeze indeed, but the cable just skates further. In Figure 9 an installation is shown of a project in Norway, at temperatures below -20 C. 58

6 Figure 9. Cable jetting with cable lubricator at < -20 C. 5. Conclusions It has been shown that lubrication of cable and (micro)duct has a large beneficial effect on cable jetting, sometimes even increasing the achievable distance by a factor of 10 (current record distance is 3.7 km in one blow ). Lubrication of microducts is not recommended for microducts with an inner diameter smaller than 5 mm (too critical and takes too long), or when installation is done in freezing conditions. Lubricating the cable is always possible, using the cable lubricators described in this paper. Three different cable lubricators are presented. The smallest one is non-dividable, does not have a lubricant reservoir and is coupled inline with the duct. It can be used to lubricate cables from 0.8 mm to 4 mm in microducts from 3/2 mm to 12/9.6 mm. The medium one is dividable, is equipped with a lubricant reservoir and is built inside the jetting equipment. It can be used to lubricate cables from 1 mm to 9 mm in microducts from 4/3 mm to 16/13 mm. Tandem jetting is possible with this cable lubricator. The large one is also dividable, contains a lubricant reservoir and is coupled in-line with the duct. It can be used to lubricate cables from 4 mm to 18 mm in microducts from 12/0.96 mm to 50/40 mm. Tandem jetting is again also possible, except for the option of jetting bundles of microducts It has been found that these cable lubricators also help against static electric charging of the cable, a well known problem for small optical cables (< 2 mm diameter). 6. Acknowledgments Special thanks to Menno Versteeg (Draka/Prysmian, NL), Fabrice Abbet, Michel Cherix, Sege Wyder, Francois Croisier and Gerard Plumettaz (Plumettaz SA, CH), for designing the cable lubricators, Maja Keijzer, Cees van t Hul, Willie Greven, Thomas Pothof, Jan Jonker, Ralph Sutehall, Alain Lavenne, Denis Raynaud (Draka/Prysmian, NL, UK and FR), Flavio Piras (Plumettaz SA, CH), Paul Lépine (CEV-Treuil, FR), Jeannette Mulder, Marcel Jansink and Laurent Lebailly (Wavin, NL and FR), taking part in jetting tests, and Sheri Dahlke and John M. Fee (Polywater, USA) for developing the lubricant. 7. References [1] W. Griffioen, A new installation method for conventional fibre optic cable in conduits, Proc 37 th IWCS (1988) [2] W. Griffioen, The installation of conventional fibre-optic cables in conduits using the viscous flow of air, J. Lightwave Technol., Vol.7, No.2 (1989), p [3] S.A. Cassidy, M.H. Reeve, A radically new approach to the installation of optical fibre using the viscous flow of air, Proc 32 nd IWCS (1983) [4] W. Griffioen, C. van t Hul, I. Eype, T. Sugito, W. Greven, T. Pothof, R. Khiar, L.K. de Jonge, Microduct cabling at CERN, Proc 53 rd IWCS/Focus (2004) [5] W. Griffioen, Understanding of Cable in Duct Installation: Do s and Don ts, Proc 60 th IWCS/Focus (2011) [6] G.C. Weitz, Prediction and minimization of fiber optic cable pulling tensions, IEEE Journal of Selected Areas in Communications, vol. sac-4, no. 5, 1986, pp [7] W. Griffioen, S. Zandberg, M. Versteeg, M. Keijzer, Blow simulation test to measure coefficient of friction between (micro)duct and cable, Proc 54 th IWCS (2005) [8] IEC 86A 1048/NP Guidance on techniques for the measurement of the Coefficient Of Friction (COF) between cables and ducts. [9] USA patents , and [10] K. Nothofer, W. Griffioen, A. van Wingerden, A. Berkers, M. Garcia S.Emeterio, O. Tatat, A. Weiss, O. Storaasli, Experience in the Application of Various Microduct Cable Designs, Proc. 54 th IWCS (2005) [11] IEC , Optical fibre cables Part 5-10: Family specification for outdoor microduct optical fibre cables, microducts and protected microducts for installation by blowing, Annex E. Document under construction in SC 86A WG3. [12] W. Griffioen, A. van Wingerden, C. van 't Hul, M. Keijzer, "Microduct cabling: Fiber to the Home", Proc 52 nd IWCS (2003) The Author Willem Griffioen received his M.Sc. degree in Physics and Mathematics from Leiden University (NL) in 1980 and worked there until Then he worked at KPN Research, Leidschendam (NL) on Outside-Plant and Installation Techniques. He received his Ph.D. (Reliability of Optical Fibers) in 1995 from the Eindhoven Technical University (NL). From 1998 to 2009 he worked at Draka Comteq, Gouda (NL), on Connectivity of FttH. Currently he works at Plumettaz SA, ZI En Vannel C, CH-1880 Bex (CH), willem.griffioen@plumettaz.com and is responsible for R&D of cable installation techniques. 59