High Capacity Conductors for Cost Effective Upgrade in Transmission Network

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Overview of ACCC Conductor: Technology, Performance and Characteristics, Transmission line design and Applications in reconductoring and new lines.

Text of High Capacity Conductors for Cost Effective Upgrade in Transmission Network

High Capacity Conductors for Cost Effective Upgrade In Transmission NetworkJason Huang, CTC, 2026 McGaw Ave., Irvine, California 92614, USA (Phone: 949 428 8500; email: jhuang@ctccable.com)

ABSTRACTCarbon Fiber Composite Core Conductor (ACCC) is a new class of conductor for the electric delivery system. It offers greater capacity, superior strength, lighter weight and lower thermal sag. It is also free of the corrosion associated with metallic cores. The superior strength of the composite core allows for the stranding of an increased quantity of aluminum in trapezoidal layers with fully annealed aluminum for maximum current carrying capacity with the lowest loss. This conductor brings important advantages where lines need uprating as well as for new lines. This conductor would be ideally suited to the challenges facing grid owners and operators, by increasing capacity through new lines or upgrades where existing infrastructure and Right of Way can be fully leveraged for cost effective capacity additions. The low line loss also makes it attractive for connecting the alternative energy source (e.g., wind or solar) to the Grid where line loss could substantially impact the business model of alternative energy sources. With over 5 years of commercial installation, it is important to consider the technology behind the conductor and the experience from the field. Unlike metallic cored or metal ceramic composite core conductors, there are unique attributes associated with the ACCC carbon fiber composite cored conductor, including its performance characteristics at high temperatures. This paper will review and discuss thermal oxidation fundamentals, testing and field experience related to temperature capability; as well as the comprehensive durability testing and longevity of composite core conductors.

1. INTRODUCTIONCarbon fibre composites are the material of choice for many high performance and demanding applications (e.g., primary structures in Boeing 787 and Airbus A350), because of their higher strength and lighter weight, and their exceptional resistance to cyclic load fatigue. The extremely low axial thermal expansion in carbon composite makes it ideal for application where controlled thermal expansion is highly desirable. The ACCC Conductor (Aluminium Conductor Composite Core) consists of a hybrid carbon and glass fibre core, wrapped with trapezoidal shaped aluminium strands. The high strength structural core carries most of the conductors mechanical load, while the fully annealed high purity aluminium strands carry all of the conductors electrical current. This patented composite core is manufactured using a proprietary continuous pultrusion process, wherein carbon and boronfree glass fibres are impregnated with a toughened epoxy resin optimized for thermal and environmental stability. The Boron-free glass fibres, surrounding the central carbon fibres, are placed in outer shell of the composite core to prevent galvanic corrosion between carbon and aluminium while improving ACCC core flexibility. The composite core is then spooled onto reels, before shipment for aluminium stranding, Figure 1 - ACCC Conductor undergoes quality control testing that ensures a minimum _________________________High Capacity Conductors for Cost Effective Upgrade in Transmission Network

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tensile and bending strength, along with a minimum glass transition temperature (Tg). With economic growth, many electrical transmission corridors in the world are overloaded and could no longer support the transmission of needed power to sustain economic growth, or allowing for power to be imported to load centres cost effectively (e.g., relatively cheap hydroelectric power could not be imported). The primary limiting factor for increasing the capacity of many transmission and most distribution lines relates to conductor thermal sag. When a conductor carries more current, its temperature rises, causing the conductor to elongate (i.e., sag) in accordance with its cores coefficient of thermal expansion. The ACCC Conductor with maximum usage of fully annealed Aluminium, was developed for optimal efficiency (lowest line loss), highest capacity and lowest thermal sag, to cost effectively increase the capacity of the electrical transmission and distribution grids. The ACCC conductors hybrid composite core exhibits a coefficient of thermal expansion about 1/8th that of a steel core (and 1/10th of aluminium core). The reduced thermal expansion decreases thermal sag and allows the conductor to carry more current without compromising clearance requirements. An ACCC conductor of equivalent diameter and weight can carry approximately twice the power of a conventional ACSR conductor. The major US east coast power outage of 2003 was caused by excessive line sag during peak summer demand conditions. The ACCC conductor technology can substantially increase the electric grid reliability by reducing the risk of such occurrence and allowing for additional power to be efficiently moved to load centres during peak demand conditions.

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Increasing Line Capacity and Enhancing Grid Reliability Using the ACCC ConductorWith clearance limitations between the conductor and the ground/vegetation/electrical underbuild/other utilities lines well established, sag associated with conventional ACSR has become the limiting factor to increase transmission line capacities at utility companies. Aside from excessive thermal sag in ACSR conductors, the aluminium strands in ACSR conductors will be annealed at high temperatures. This will lead to substantial loss in strength and stiffness of the ACSR conductor (aluminium strands could account for as much as 50% of the ultimate strength in some ACSR conductors), further exacerbate creep and sag in these conductors. While other conductors such as ACSS Aluminum Conductor Steel Supported utilize preannealed aluminium strands, allowing them to operate at much higher temperatures without degrading their rated strength, ACSS also sags substantially at higher temperatures due to its higher coefficient of thermal expansion in the steel core. ACSS conductors typically involve extra weight from its steel core. When ACSS conductor is utilized as a replacement for ACSR conductor, the supporting structures often require reinforcement or replacement. This is also true when a larger / heavier conductor is used to replace an existing conductor to improve the lines capacity. Upgrading or replacing existing structures can be very difficult and expensive especially in remote locations with difficult access or terrain, or in more populated areas where under-built electrical and communication lines can be extensive. In applications where metal corrosion is a concern, the higher operating temperature for metal core conductors could further limit the longevity of such conductors. The ACCC Conductor is ideally suited to upgrade existing transmission and higher voltage distribution lines due to its mechanical strength, thermal stability, and improved conductivity compared to any other conductor type of the same diameter and weight. The ACCC conductor offers a less expensive alternative to increasing line capacity, as it can be installed without requiring structural modifications. An ACCC conductor of the same size (OD) and weight can be operated at emergency temperatures of as high as 200 oC, offering the highest capacity among all the comparable conductor options (including running the other HTLS conductors at substantially higher temperatures) without exhibiting significant thermal sag (in Figures 2 and 3), as demonstrated in a conductor comparison test conducted at Kinectrics Lab, Canada, as part of a Hydro One study, where several types of Drake (28.15 mm OD) sized conductors were compared to ACSR conductor under a 1600 amp load. The unique attribute of highest capacity with lowest thermal sag in ACCC conductors, could substantially improve the capacity of the grid to handle emergency conditions (N-1 and N-2), as well as the transient nature and the peak loads from alternative energy sources (solar and wind powers), thereby enhance the grid reliability.

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Figure 2: The ACCC conductor carries more current than any other conductor at the same temperature, and delivers more peak capacity than other conductors, even when they are operated at much higher temperatures. It is important to note that one does not have to run the conductors at extremely high temperatures to obtain the required capacity. The High Capacity Low Sag ACCC Conductor provides the option to the electric utility customers to obtain the necessary capacity for emergency conditions without having to operate its system at the extreme temperatures required for other types of conductors of similar size and weight.Temperature (C) 00

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Figure 3 - Sag and Temperature Comparison between Different Types of Conductors (1600 amps)

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Minimizing Line Loss, Improving System Efficiency and Avoiding CO2 Emission Using the ACCC ConductorThe Hydro One Sag Test also noted that the ACCC conductor ran 60 to 80 oC cooler than the other conductors tested under the same load (1600 A). This cooler operating temperature is a direct reflection of the ACCC conductors greater efficiency compared to the other conductor types. This