Frequently Asked Questions
1 About ACFR® conductor
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Most carbon fiber composite core HTLS conductors have increased aluminum content with lower sagging characteristics, however, one notable characteristic of ACFR conductor is its flexibility of the stranded CFCC core (The CFCC is a 7-strand core, with a relatively short lay-length, for increased flexibility and robustness), which provides better handling characteristics, damage tolerance and most importantly, the conductor can be installed using conventional ACSR installation methods without significant increase in cost and time. It is an object of the technology to provide a conductor having increased flexibility which translates into practical workability.
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Carbon fiber composite material offers higher tensile strength, much lighter weight, corrosion resistance, and lower coefficient of linear expansion as compared to steel. It also does not exhibit fatigue failure or creep characteristic over time like steel materials do. In addition to the superior characteristic of the material, our object was to add flexibility and better damage tolerance by incorporating multi-strand CFCC. Through extensive R&D and trial installation efforts, we believe that practical handling characteristic of the conductor leads to assuring safety and quality during installation, which leads to timely construction and longevity of the conductor.
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Most of the projects have been a need to upgrade the current-carrying capacity, typically by 50-100 % rating increase. But there are a few projects where the main target was to increase the clearance by lowering the sag. Like any other HTLS conductor, there are various application cases where ACFR can improve the efficiency of power grids, using advantages of high temperature operation, lighter weight, lower sag, as well as corrosion resistance. Added flexibility of ACFR allows conductors to be installed in challenging environments, using conventional methods, including semi-tension, layout and manual stringing methods with no significant increase in installation cost and time. Common application cases are:
- Uprating current carrying capacity or lowering transmission losses: Reconductoring, using existing infrastructure to increase current capacity or lowering transmission losses (which also translates into reducing CO2 emission or power generation cost).
- Sag improvement while maintaining equivalent current carrying capacity: Reconductoring, using existing structures where extra clearance/sag improvement is needed.
- Improving longevity of the conductor in highly corrosive environments: Replacing existing conductor with ACFR, A) and/or B) can be added.
- Reconductoring by semi-tension or layout method in hilly regions where transportation of tensioner and puller is difficult or costly due to limitation on accessibility to sites, A) and/or B) or C) can be added.
- Reduction on initial cost for newly constructed lines: Lighter & smaller ACFR conductor can reduce the number (or lower the height) of structures for newly constructed lines.
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Several type tests have been performed on the CFCC core by Tokyo Rope International (TRI), completed conductor and conductor systems using the CFCC core (by several conductor manufacturers). Please refer to R&D, Testing & Monitoring pages for more details.
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The ASTM B987 standard have been used and tests performed to this on the CFCC with a couple of exceptions since the stranded core is different than a pultrusion rod. There is no international standards yet on the full conductors with composite cores and other standards are generally used where applicable. Please refer to R&D, Testing & Monitoring pages for more details.
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The ASTM B987 standard have been used and tests performed to this on the CFCC with a couple of exceptions since the stranded core is different than a pultrusion rod. There is no international standards yet on the full conductors with composite cores and other standards are generally used where applicable. Please refer to R&D, Testing & Monitoring pages for more details.
- 20 + years of successful operation track record.
- Detailed scope by scope installation guideline.
- Crew training prior to construction and on-the-job training for new installers.
- Hardware assembly training.
- On-site installation support services by experienced installers.
- Stress-strain and creep test reports to support PLS-CADD® and wir files and SAG10® charts.
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The carbon fiber material itself is non-corrosive and degradation of the CFCC core, that results in tensile strength reduction during its lifecycle, is minimum. Unless the CFCC core is overheated (capability showed in the Heat Exposure, Heat Stress tests and Arrhenius method), it is unlikely that the CFCC will fail before the aluminum eventually corrodes. We have evaluated that the galvanic corrosion is negligible with the polyester protection (Refer to salt spray tests). Heat exposure tests were performed for up to 10,000 hours with temperature of 180, 200, 220, 240 degrees Celsius. As per the thermal limits based on Arrhenius model from the lab data, expected lifetime of CFCC core far exceeds 100 years, but eventually the aluminum will corrode by normal exposure to the environment (pitting, crevice). Therefore, we expect the conductor to last at least as long as your conventional conductors lasts in your system.
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Tokyo Rope’s carbon fiber composite cable, CFCC, was originally developed during the 1980s as tension members for the civil engineering applications (e.g. pre/post tension cables in bridges, ground anchors and suspension cable). An enhanced version of CFCC for overhead conductor core was later developed with high-temperature resistance in the late 1990s. The first ACFR demonstration lines were installed in Japan in 2002 and 2003. To our knowledge, these were the first commercial conductor installations with carbon fiber core worldwide. The 2002 installation was dismantled and evaluated after 16 years of operation and the dismantled conductor showed satisfactory performance in corrosion resistance and remained tensile strength. A second demonstration line was installed in 2003 and is still operating as of 2024 without any issue.
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Reduction of tensile strength of our CFCC core under wet condition was not observed after 20 years of wetting (submerged in a pond at our factory). A water absorption test on CFCC core showed negligible weight gain.
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A resin encaged polyester protection layer is applied to each of the 7 individual core wire's for galvanic protection between carbon fibers and aluminium.
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The maximum continuous operating temperature is 180 °C. The maximum emergency temperature is 200 °C.
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Considering that our stranded CFCC cores ranges from the smallest 5.3 mm core to the largest 21.2 mm core, our conductor manufacturing partners can supply conductors in a variety of sizes and ampacities, suitable for both high-voltage transmission grid infrastructure as well as distribution grid needs. Conductor designs include round wires or trapezoidal shaped wires. Due to the ice load ratings, conductor designs with a thermal aluminium alloy will be recommended to be used in some regions. We can also create a new conductor sizes custom fit for specific requirements. Please refer to “options” in our ACFR Conductors pages or contact TRI for further discussion.
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The aluminium strands will take some of the tension load when conductor is operated below the “knee point” temperature, and above this knee point, all the tension load is transferred to the composite core. For designs with fully annealed aluminium, almost all the strength will be in the carbon core as transferring of tension load to the core occurs at relative lower temperature.
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1219m across the Mississippi river in the U.S. is the longest span that ACFR is installed.
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Lead times can vary depending on project size and production capacity of conductor manufacturers. Our core manufacturing plants are located in Japan and in the U.S. and our manufacturing capacity is substantial. TRI try to support a timely delivery of conductor and hardware worldwide in conjunction with manufacturing partners. Both the individual supply of conductor and fittings, and a complete system supply is possible.
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We usually provide conductor designs and studies based on PLS-CADD for customers considering their specific parameters and needs. Normally our designs are customized and optimized. We will be happy to perform such studies and optimized designs. Data sheets and WIR files are available upon request.
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ACFR conductors will be supplied on similar drums as regular AAAC and ACSR conductors. Due to the stranded CFCC core, special drums with larger diameter is typically not needed. We recommend a drum diameter of minimum 40 x Dc. The conductor can be shipped on steel or wooden drums whichever is specified. We recommend storing the drums outside only for a limited time. This is particularly important for wooden reels, but steel reels may be protected by wooden slats which may not last for long outside.
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Please contact TRI for further discussion in detail. Our production engineers can support new stranding partners, who wants to diversify product line-ups, by providing technical support to start production, initiate a track record with a pilot line, and progressively move on to full implementation projects.
2 About ACFR® core
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It is an object of the technology to provide a carbon fiber composite core having increased flexibility, suitable workability, better damage tolerance, and structural redundancy without handling characteristics penalty. Unlike pultrusion process, stranding carbon fiber requires technical know-how with precision and consistency, and we have reasons to believe that practical handling characteristic and better damage tolerance should be prioritized. Normally fewer carbon fibers will not be a limiting factor, however, if needed, higher strength core can be manufactured with higher strength fibers.
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Most of the listed tests are special and in particular developed to show performance of the special conductors operating at high temperatures: Stress-strain at elevated temperature, High temperature sag-tension, High temperature endurance, Thermal cycles with tension, UTS at high temperature. While different conductor manufacturers have performed different tests as a response to a customer requests, not all tests need to be repeated in general but shows that the technology works in general.
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CFCC uses overlapped polyester yarn （PET） wraps (min. 0.05mm thickness) as galvanic protection of each strand. Field and laboratory evidence over the past 20 years for overhead lines application (and 30 years for civil engineering applications) have demonstrated superior galvanic protection performance of the CFCC core, and there has not been a single example of corrosion issue associated with the overlapped polyester yarn wraps. In addition, the CFCC core has passed relevant ASTM B987/ (except for galvanic protection layer thickness and material since it is not applicable) and CIGRE B426 requirements, passed the severe AEP sequential mechanical test (finished conductor) along with numerous other conductor tests, passed acid and alkali exposure tests far in excess of OHL extreme environments, and passed water absorption test with negligible weight gain. Numerous corrosion tests, including 20-year field exposure test, have demonstrated far less aluminum corrosion than a cohort ACSR conductor in the same exposure, showing that the protection performance of CFCC far exceeds the benchmark of the conventional galvanized steel core used in ACSR. One of the 2000-hours salt fog tests demonstrated adequate protection of the aluminum strands even with the protection layer removed. The ACFR conductor was still in serviceable condition, showing that the polymer matrix resin provides a considerable degree of galvanic protection as well while cohort ACSR was severely degraded and unserviceable after exposure in the same test condition.
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In general, all type testing performed on the CFCC core and most type testing on the finished conductor has been carried out at 3rd party independent Labs.
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No, there are no permanent joints in CFCC cores. However, TRI supply CFCC in lengths of more than 7.2 km so it should not be necessary. In case that it is preferable to temporarily connect the CFCC core for continuation of manufacturing conductors, it is recommended to clearly mark the location of the connection, as part of production quality control, so the finished conductor will be complete without joints on core.
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Yes, it is possible to 100% recycle the conductor including the CFCC core. We have started recycling all CFCC scrap from our USA factory. The CFCC is chopped in smaller pieces and the polymer resin is burned away. The carbon fibers can be used for different reinforced plastic products or reinforced concrete. CFCC recycling has been done only in the U.S. as of 2024.
3 About ACFR conductor hardwares and accessories
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ACFR conductor uses compression-type dead-ends and splices for most designs which can be installed using conventional dies and presses. All fittings that are in direct contact with the conductor must be rated for HTLS and approved for ACFR type conductors. It must handle the higher current and hold the CFCC core. 2-piece compression fittings work well with the CFCC core, where a small inserted soft aluminum tube (or bottom layer of annealed-aluminum strands), can hold the core so no advanced holding mechanism is needed. It is also possible to use a Wedge type fitting. Qualified hardware and accessories are available from several suppliers. Please refer to hardware manufacturer’s recommendations for installation procedures, required tools & equipment and quality control parameters. Further details can be found in our ACFR
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The type of core-gripping buffer is determined based on conductor design. An annealed aluminum core-gripping buffer tube (separate insert) is typically used when the bottom layer of the conductor is not annealed soft aluminum, and/or have round wires that are not suitable as core-gripping components. Installer should check with manufacturer’s recommendation.
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We recommend AGS type suspension with armor rods in general. However, high-temperature cushion type grips can be used subject to type testing.
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It is required to support the conductor at two points to avoid sharp bending by single-hooking when installing armor rods. Using lifting beams or conductor grips on both sides are recommended. The length of lifting beam / distance between conductor grips should be longer than the armor rods.
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A vibration study should be performed and dampers installed as per manufacturer’s recommendations and damper placement chart. In general, more than 800mm - 1000mm spacing between the edge of armor rod (if required) and the Dead-end / Suspension clamp is required as to allow the aluminum strands to move to avoid fatigue breakage caused by aeolian vibration or galloping of the conductor. For damper placement in the span, it is important to avoid symmetric spacing, as the dampers can cause unwanted movements in the span.
4 About ACFR conductor installation
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ACFR can be installed using almost the same installation equipment and procedures as is used for conventional conductors. No special tools and/or equipment are required other than slightly oversized running sheaves. Further details can be found in our ACFR installation guideline. TRI also provides pre-construction training as well as on-site training and installation support services upon request to ensure that the optimal solution is fully realized by end users.
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Yes, and we propose to provide initial training: The site supervisor, foreman, and lineman should go through ACFR installation training provided by TRI installation specialist and/or Conductor & Fitting manufacturer prior to the installation. It is typical that TRI has an Installation advisor present during the installation. For repeat installations this may not be needed but can be arranged.
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Conductor can be supplied in specific requested lengths as needed. Maximum conductor length will depend on the conductor size. In terms of the CFCC core lengths, these are 7.2 km and e.g. supply of 3.6 km or 2.4 km drums would be efficient.
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Yes, it is possible to use existing conductor to pull in the conductor if it is assured that the existing conductor is entirely free from any damages and some caution to avoid transferring torsional stress from the old conductor is used. We recommend a small section of anti-twist pulling wire in the front-end and including a free-rotating swivel between this and the existing conductor to release torsional stresses, as well as swivels between each drum. Further details can be found in our ACFR installation guideline.
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The minimum bull wheel diameter is 40 x Dc.
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The minimum stringing wheel / sheave diameter is 20 x Dc in general (up to 60 degree angle). At high angles, a larger diameter or sheaves in tandem may be needed. Please refer to details in our ACFR installation guidelines.
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Yes, a line section can be repaired in manners similar to ACSR conductors, but extra consideration should be taken to keep the core intact. If it is minor damage to outermost strands, repair rods or a repair sleeve can be installed to restore conductivity of the conductor. For more substantial damage, or if the extent of damage indicates that the underlying aluminum layers also have experienced excessive bending or twisting, the damaged portion should be cut and removed and full tension joints can be installed. Please refer to details in our ACFR installation guideline.
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There are three ways that CFCC core can sustain damage: a) excessive sharp-bending, b) over-twisting, and c) over-compression, and these will result in damage or distortion of aluminum layers such as, opening of outer strands, bird-caging, snaking (squeezing), and breakage of aluminum strands which all can be spotted visually. It is advisable to carefully check the condition of aluminum strands prior to sagging. As the core of ACFR tend to be interlocked with the bottom layer of the aluminum strands, the extent of damage on the core is often interlinked with the extent of distortion of aluminum layers which can be spotted visually (by looking for opening of strands, bird-caging, and snaking/squeezing). The CFCC core is unlikely to be damaged without distortion of aluminum strands. No example of damage or breakage of the core without distortion of outer aluminum strands has been reported.
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Sharp local bending of ACFR conductor should be avoided during lifting of conductor, replacing insulators, replacing suspension clamps, and installation of dead-ends. Please refer to our ACFR installation guideline for more details.
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Jumper conductor does not have to bear tension, more than the weight of the conductor itself, and the core of ACFR does not have to function as tension bearing components, therefore, restriction on bending radius does not really apply in terms of keeping mechanical strength. Important things are: maintaining aluminum strand condition and conductivity of the conductor and required clearance. ACSR jumpers can be used if it can achieve the same rating without having “hot spots” at the jumper connections. Aluminum adjustment plates for bolting connections of the ACSR jumper terminal - ACFR dead-end clamp may be needed in case holes do not match.
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Yes, it is no problem to travel out on conductor as line cars usually have multiple supporting rollers which will not cause sharp bending of tensioned conductor. Care shall be taken for annealed aluminium to maintain surface condition but it is not critical for AT1/AT3 or hard-drawn aluminum.
A1: Conductor breakage by over-twisting during installation:
During an early ACFR installation, back-to-back pulling of the conductor for more than 10km without torsion releasing technique through poorly maintained running sheaves caused breakages of ACFR conductors by over-twisting at multiple locations. Causes were as follows: excessive pulling length, improper use of running blocks, lack of torsion releasing means and inconsistent back-tensioning operation caused excessive accumulation of torsional stress (over-twisting) within a relatively short length of the conductor. The length of the back-to-back pulling section was more than 10km which caused higher pulling tension to maintain clearance (and more torsional stress in the conductor as it tends to unwind itself when pulled with higher tension). Some of the running blocks used in the section were poorly maintained (some were not even in rotating condition with rusty bearings and the conductor was being dragged over the grooves during pulling). Also, the position of the running blocks at angles were not adjusted in a manner that the conductor runs in the center of the groove which caused even more torsional stress on the conductor as it was rotated by the friction with the wall of the groove when pulled through angles. Torsion releasing swivel between the drums and counterweight at the head of each drum were not used as the connection between drums were done by permanent conductor splices installed at the tension site. All these factors combined, torsional stresses kept accumulating on the conductor during the pulling operation which eventually caused excessive twisting of the ACFR conductor within a relatively short length, when the pulling tension was increased and dropped dramatically. All the breaks were in the same section installed by same installer.
Countermeasure:
TRI’s installation support personnel provided feedback and recommended corrective actions. All the tools and equipment were inspected and any portion of the conductor with aluminium distortion (evidence of over-twisting) were cut and replaced with new conductor. The installation specialist provided scope-specific on-the-job training and detailed recommendation for: selection of sheaves, torsion releasing technique as well as dividing the pulling sections into < 20 spans. All the poorly maintained sheaves were removed from the sites and replaced with properly working sheaves and position of sheaves at angles were readjusted, torsion releasing swivels and anti-twist counterweights were used in between drums, and conductor splices were installed after the conductors were pulled into place. TRI’s installation experts remained on site until it was assured that all members of the installation team became aware of the specific cautions and limitations of the conductor for each scope of work. The rest of the installation was resumed without any issue. The line has been energized and operating without any problem after installation to this date. Scope specific preventive cautions were added in our ACFR installation guideline.
A2: Conductor breakage by over-twisting after installation:
Conductor breakage occurred at one location 3 years after installation. After investigation of the broken portion of the conductor, it was concluded that the CFCC at the location of the breakage had already been sheared by over-twisting of the conductor during the installation so the core was not fully functioning as tension bearing member. The tension on the conductor (approximately 2 tons) was taken by the outer aluminum strands (almost 90% UTS of the aluminum strands combined) which eventually led to the breakage by creep rapture of aluminum strands after 3 years. The causes of damage were (similar to aforementioned case): excessive pulling length, improper use of running blocks, lack of torsion releasing means and inconsistent back-tensioning operation which caused excessive accumulation of torsional stress (over-twisting in loosening direction of outermost layer). Although the sign of distortion of aluminium was evident, the twisted portion of the conductor was repaired in a manner to restore the conductivity of the aluminium strands but not the tensile strength of the core (replacing the distorted portion with new conductor or full tension splice is recommended). The line was installed by the same crew that experienced conductor breakage during the installation mentioned above.
Countermeasure:
TRI provided additional training for the crew members to reinforce the best installation practices. The very same crew successfully completed another reconductoring project without any issues during and after the installation and no issues or problems have been reported on the line. Any portion of conductor with sign of overtwisting (birdcage and/or squeezing) were identified and replaced prior to energizing.
A3: Failure of incorrectly pressed dead-ends during and after installation:
Conductor slipped out from dead-end clamp during and after installation. Two different dead-end fittings (which require different die sizes) were used for the project (due to some delays in delivery of initially scheduled fittings). Slightly larger sized die was specified for the initial fittings (across-flat-width after compression was 18.90-19.20mm for the initial fittings and 18.75-19.05mm for the newly added fittings). After investigating the failed fitting, it was found that some of the inner steel sleeve of newly added fittings were compressed with wrong dies (which was prepared for initial fittings), resulting in insufficient compression (gripping of the composite core) of some of the steel sleeve (which in general provides 80 % of the RTS of the dead-end (the rest, 20% comes from the aluminium sleeve). It was then communicated to the installation crews that it must be verified that across-flat width of steel sleeves after compression must match with the manufacturer’s specification. However, some completed dead-ends were overlooked and not corrected prior to completion. Main causes of this issues were lack of communication and installation quality control failure.
Countermeasure:
Double-checking across-flat-width after compression was included in the quality control procedures/method statements and dies and press, as well as fittings, were marked with matching identifications to avoid unnecessary confusion. It was instructed that installation tools and equipment, procedures and QC parameters to be reviewed and verified at daily toolbox meetings. The rest of the dead-ends, where it could not be assured that the inner sleeve was compressed with correctly sized die, were replaced with properly installed dead-ends. No failure of conductor nor fitting have been reported on the line after the corrective actions have been taken.
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Three cardinal rules of preventive cautions for installing ACFR conductors are: to avoid sharp bending and over-twisting of the conductor, avoid excessive compression force on the core, and avoid excessive and/or insufficient compression of the core during installation of dead-ends and splices. Examples of handling mistakes and scope-specific cautions and quality control points can be found in our ACFR installation guidelines.
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The conductor may be pre-stretched prior to sagging in some applications when it is desirable to sag the conductor according to its final condition by stabilizing the elongation of a conductor for some defined period of time. However, as the prestressing tension is normally higher than the unloaded design tension for a conductor (the pre-tension value is specifically calculated for each installation and temperature and conductor is pulled up to specified tension and held for certain periods of time (e.g. 30min. to one hour). Then the creep elongation will be temporarily halted (or completely halted depending on design and tensions). It is not always recommended as this method may present both equipment and safety problems and it shall be assured that the structure, sheaves and support hardware are capable of withholding the applied tension if pretensioning used. In general, it is recommended to tension the conductor at 90%+ of initial sag tension, allow the conductor to remain at this tension for at least 10 hours or overnight and crimp-in within 72 hours after the conductor is pulled into place. In case that sagging must be done same day, subtracting 5-10° C from the conductor temperature in the sagging chart is commonly used practice.
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ACFR splices are normally installed only after conductor has been pulled into position as it is recommended to release torsional stress by swivel in between drums. In case that installation of splices after conductor is pulled into position is not possible, splices may be installed at the tension site. Detailed recommendations for puling preinstalled splices can be found in our ACFR installation guideline.
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Core-retainer is recommended for pulling 0-temper aluminum conductors (or conductors having round aluminum wires instead of trap wires) but not necessarily required for AT1/AT3/hard-drawn aluminum conductors. The core retainer is used to keep the underlying layers (and the core) from slipping inside stretched outermost aluminum layers as soft annealed 0-temper aluminum are more prone to stretch when pulled with higher tension. The core itself tends to be interlocked with the bottom layer of the aluminum strands and is less likely to be displaced. Stretching of outer layer strands of annealed aluminum conductor can exceed 200mm or more when pulled without a core retainer (depending on pulling tension) which might cause reduction of gripping strength of the mesh-sock while the extent of stretching of outer strands of AT1/AT3/hard-drawn is a lot less than that of 0-temper and often negligible (10-20mm). However, it is recommended to check the gripping strength of the mesh-sock conductor grip prior to use. Further details can be found in our installation guideline.
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Distance between ground wire/OPGW above phases should be taken into consideration during the design phase.
