The full name of carbon fiber conductor is carbon fiber composite core aluminum stranded wire (ACCC). This conductor has been used since the beginning of this century. It has only been used for more than ten years and has certain application experience. Carbon fiber conductor has the characteristics of high strength, light weight, high elastic modulus, small linear expansion coefficient, small sag, small line loss, large ampacity (high allowable temperature), corrosion resistance and long service life. It is especially suitable for the use environment with high corrosion intensity, high pollution intensity and easy conductor galloping in coastal and mining areas.

 

The development background of the conductor is that the transmission capacity of the original transmission line can not meet the rapid growth of load. It is imperative to replace the conductor with large section and large carrying capacity or build a new special line. The traditional methods of dismantling old lines, transforming towers and erecting new conductors have high cost and long construction period, or it is difficult to land acquisition under the original line channel, resulting in that the new line will not be able to use the original line channel, which brings great difficulties to power grid planning and construction, improves the project cost to a certain extent and prolongs the construction period; The long-term power failure during line erection also greatly affects the power supply reliability and equipment availability coefficient of the power grid. In order to solve the above contradiction, it is the only way to find an engineering construction method that can not only make use of the original line channel, but also minimize the tower transformation, but also greatly improve the line transmission capacity. In this case, there is a carbon fiber conductor.

 

Carbon fiber conductor has many advantages, but it also has its disadvantages. For example, most carbon fiber conductors have carbon fiber core single core (it is understood that carbon fiber core strand is being developed). It is easy to be damaged in construction. It is not suitable to be found inside the aluminum strand. After being damaged, it will leave a little potential safety hazard for future operation. Today, Xiaobian will share with you some cases of problems that are easy to occur, mainly in the construction stage, and briefly explain some precautions in operation.

 

Defect type 1: surface burr

 

Introduction: the capacity of a 500kV overhead transmission line was increased and transformed, and the original steel cored aluminum strand was replaced with carbon fiber conductor. During construction, after the arrival of carbon fiber conductor, the opening acceptance is carried out, and burr is found on the conductor surface.

 

Cause analysis: there are defects in the manufacturing process of the manufacturer, resulting in burrs on the conductor surface.

 

Consequences: corona and tip discharge will be caused after the line is put into operation.

 

Suggestion: the materials shall be accepted one by one after arrival.

 

Defect type 2: Broken Strand

 

Introduction: the capacity of a 500kV overhead transmission line was increased and transformed, and the original steel cored aluminum strand was replaced with carbon fiber conductor. During the stringing construction, it is found that there is a broken strand of the conductor, and no construction stress trace is found at the broken strand.

 

Cause analysis: there are defects in the manufacturing process of the manufacturer, resulting in broken strands of wires when leaving the factory.

 

Consequences: after the line is put into operation, there will be loose shares and stock throwing.

 

Suggestion: the materials shall be accepted one by one after arrival, and the three span section shall be mainly accepted.

 

Defect type 3: "lantern", drum

 

Introduction: a 220kV transmission line capacity expansion and reconstruction project × Lgj-400 / 35 steel cored aluminum strand conductor is replaced with 1 × Jrlx / T-400 carbon fiber conductor. During the stringing construction, the conductor "lanterns" and bulges appear.

 

Cause analysis: the carbon fiber conductor is twisted from the inner carbon fiber core and the outer aluminum wire. During the spreading or tightening process of the carbon fiber conductor, the aluminum wire on the surface of the carbon fiber conductor will "creep elongation" (there will be a gap between each strand of the aluminum wire. The stress will make the strands of the conductor closer and the gap smaller, although the length of the conductor changes, However, the whole conductor is elongated), and the inner carbon fiber mandrel has low deformation due to its high strength. The outer aluminum wire and the inner carbon fiber mandrel will slip relatively. When the slip is obstructed or after the crimping of one side tension clamp is completed, the aluminum strand on the surface of carbon fiber conductor will appear "lantern" (bulge).

 

Consequences: (1) there are "lanterns" (bulges) in the aluminum wire of carbon fiber conductor, which is generally difficult to repair the running line. After the aluminum wire is loose, the carbon fiber core is also exposed to the air for a long time. If the operating environment is bad, it is unfavorable to the carbon fiber core（ 2) The aluminum wire has "lanterns" (bulges). Due to the change of tension during operation, the stress on each layer of aluminum wire on the surface will be uneven, resulting in broken strands of aluminum wire.

 

Suggestions: (1) different technical indicators of each conductor manufacturer in the processing process will lead to different twisting tightness of the finished conductor. The manufacturer's technical disclosure shall be carried out before operation, and the conductor shall be laid and tightened in strict accordance with the manufacturer's operation requirements（ 2) During the construction of wire tightening and hanging, special pre twisted tension tools shall be used to reduce the use of puller and wire clamp and avoid stress concentration（ 3) During the construction of large tension section, before the drawing and printing of tension section, under the condition of meeting the line length of tension section, the remaining wire of conductor at the tension side shall be disconnected and then tightened, so that the "creep elongation" aluminum wire can run away at the disconnection as far as possible.

 

Defect type 4: broken wire

 

Introduction: a 220kV transmission line is expanded and reconstructed, and the original 2 × Lgj-300 / 25 steel cored aluminum strand conductor is replaced by 240 / 30 double split carbon fiber composite cored aluminum strand conductor. In the process of stringing construction, all wires are broken from the crimping area (near the pipe orifice) of the tension clamp after hanging.

 

Cause analysis: after relevant tests, dissecting the broken wire tension clamp and other methods to verify the cause of the broken wire, according to the test conclusion, there are mainly unqualified problems in the radial voltage withstand test of carbon core of carbon fiber conductor. The national standard GB / T 29324-2012 and the national grid standard Q / GDW 1851-2012 all require that the radial withstand voltage standard is "cut off the composite mandrel with a length of not less than 100mm, load it stably to failure at the loading speed of 1mm / min to 21mm / min, the composite mandrel shall bear a pressure of not less than 30KN, and its end shall not crack and peel"), but the tested carbon fiber conductor does not meet this requirement, The carbon fiber core produced by the supplier of this type of conductor can not meet the standard requirements. At present, most domestic suppliers have only the radial withstand voltage test requirements of carbon rods in the national standard Φ Carbon rods with specifications of 7.5 and above can meet the requirements, right Φ 6. It is difficult to meet the requirement that the specimen is 100mm and not less than 30KN. Based on the relevant test conclusions and investigation, the analysis of the causes of wire breakage mainly focuses on the possible overvoltage and other crimping process problems in the crimping process, as well as the quality problems of conductor products.

 

Consequence: disconnection

 

Suggestion: during the construction of carbon fiber conductor, the relevant provisions in the guidelines for construction technology and acceptance of carbon fiber composite core overhead conductor (Trial) shall be strictly implemented.

 

Defect type 5: external scratch

 

Defect description: during the capacity expansion and reconstruction of a 500kV transmission line, the original lgj-400 / 35 steel cored aluminum strand conductor was replaced with jlrx / f2a-460 / 40-26 carbon fiber conductor. The conductor was worn and cracked during the completion acceptance of the line.

 

Cause analysis: the soft aluminum on the outer layer of carbon fiber is scratched and scratched by sharp objects during transportation and deployment.

 

Consequences: it will affect the appearance quality and produce corona. In serious cases, the conductor will be burned and even lead to wire breaking accidents.

 

Suggestion: the materials shall be accepted one by one after arrival, and the wires shall be accepted one by one after spreading.

 

Defect type 6: loose stock

 

Defect description: during the capacity expansion and reconstruction of a 500kV transmission line, the original lgj-400 / 35 steel cored aluminum strand conductor was replaced with jlrx / f2a-460 / 40-26 carbon fiber conductor. It was found that the conductor ran strand during the completion acceptance of the line.

 

Cause analysis: when the conductor passes through the pulley during the laying process, it is squeezed and loose due to too small laying angle or mismatched pulley model; After the wire is laid out, the wire is lifted too tightly during the installation of accessories, and the wire is twisted, resulting in loose strands.

 

Consequences: it will affect the appearance quality and produce corona. In serious cases, the conductor will be burned and even lead to wire breaking accidents. It also affects the strength of the conductor.

 

Suggestion: the materials shall be accepted one by one after arrival, and the wires shall be accepted one by one after spreading.

 

Defect type 7: wear

 

Defect description: during the capacity expansion and reconstruction of a 500kV transmission line, the original lgj-400 / 35 steel cored aluminum strand conductor was replaced with jlrx / f2a-460 / 40-26 carbon fiber conductor. During the completion acceptance of the line, it was found that there were annular wear marks at the tail end of the pre stranded wire.

 

Cause analysis: first, the last few strands of the wire are not easy to be in place when binding the pre stranded wire, which is scratched when prying with tools such as screwdriver; second, the position is found to be wrong after binding the pre stranded wire, and the construction protection is not in place when removing the pre stranded wire again, which damages the wire.

 

Consequences: it will affect the appearance quality and produce corona. In serious cases, the conductor will be burned and even lead to wire breaking accidents. It also affects the strength of the conductor.

 

Suggestion: the acceptance of the conductor near the pre stranded wire should be strengthened.

 

Summary

 

Through the summary of 7 types of defects in the above three projects, the following two problems are found:

 

1. Due to the quality problem of carbon fiber, some product parameters are unqualified due to the manufacturer's failure to process in strict accordance with the corresponding procedures and specifications, which brings unpredictable hidden dangers to the construction process and even operation.

 

2. Due to poor construction technology, some construction units still use the traditional conductor construction method, resulting in bulging, strand breaking and even wire breaking of carbon fiber conductor.

 

The above two problems pose certain potential safety hazards during operation, especially product quality problems. According to the current case, the main reason is that the carbon rod does not meet the specification requirements. However, the carbon rod is the bearing part, and the unqualified carbon rod is bound to reduce the mechanical performance of the conductor. Even if the construction process is good and bad working conditions are encountered during operation, the wire breaking accident is very easy to occur.

 

As an operating unit, the following matters need to be paid attention to in the application of carbon fiber:

 

1. Although carbon fiber conductor has been developed for more than ten years, it is not widely used in the project and lacks operation experience. Carbon fiber conductor is not recommended for important spans and large spans. Aluminum alloy core high conductivity aluminum stranded wire with the same current carrying capacity can be selected.

 

2. Strict preliminary design review, especially for capacity increase projects, must have a detailed comparison and selection scheme of conductors, and carefully select carbon fiber conductors. For the project to determine the use of carbon fiber conductor, understand the positioning temperature and maximum allowable temperature of carbon fiber conductor provided by the designer, understand the corresponding conductor sag characteristics, as well as the selection method of conductor connector, etc.

 

3. In order to ensure the safe and reliable operation of the tension section where the important crossing is located, carbon fiber conductor shall not be used for the important crossing in principle, and aluminum alloy core high conductivity aluminum stranded wire with the same current carrying capacity can be used.

 

4. Strictly implement the guidelines for construction process and acceptance of carbon fiber composite core overhead conductor (Trial), master the crimping process of the construction unit, spot check the crimping quality, route the 500kV Line step by step, take photos along the 220kV line by UAV, do a good job in the acceptance of intermediate links and completion links, and control the acceptance.

 

5. For the places where the construction unit has hard contact with the carbon fiber conductor during construction, such as the position where the wire clamp is stuck on the conductor, put forward trace recording requirements to avoid wrangling after problems.

 

6. For the carbon fiber line that has been put into operation, try to avoid using flying outgoing line during maintenance to prevent aluminum strand deformation, and properly prepare some high-temperature pre twisted repair strips suitable for carbon fiber conductor strand breakage.

 

7. Explore a practical method that can detect the damage of the mandrel. Because the mandrel is currently a single core, there is no effective detection means from the beginning of damage to wire breakage. Therefore, it is imperative to explore effective detection methods and master the law of the development of carbon rod damage.

 

8. Advocating the concept of full life cycle of carbon fiber conductor operation, comprehensively mastering the operation situation, evaluating the operation situation and inferring the remaining operation time from the beginning of operation is also a very key problem, because once the carbon fiber conductor enters the end of life, it is equivalent to a time bomb for the operation unit. Therefore, it is suggested to consider it from the perspective of full life cycle, Master the best operation time of carbon fiber conductor, provide strong support for subsequent replacement, and avoid replacement after major failure.

 

As a new type of conductor, carbon fiber conductor has a very good effect on capacity expansion and transformation. It is expected that old lines will be used in large quantities in the industry in the future. However, due to the lack of operation experience, the operation unit generally holds a conservative attitude towards such products, because faults such as disconnection will bring huge safety pressure to the operation unit.

 

(source: China telecom cable network)