ACCC vs ACCR vs ACSS
Testimony from an expert witness regarding the use of composite core conductors below. The key point to pick up from this testimony is the same old story - utilities and expert witnesses play it safe. Things take time in this industry - I wonder if the witness would have given the same testimony after the Energy Act of 2005 passed and after attending the ACCC installation hoe down in Texas. I believe he would sing a diffrenet tune.
His testimony and this project can be multiplied 100 or more times around the USA. What's missing from this testimony and what I believe will be common place questions in the future:
Q. Does the ACCC cable meet the ADVANCED TRANSMISSION TECHNOLOGIES standards set forth by the energy policy Act of 2005?
A. Yes, in fact the ACCC product was written into the legislation and will qualify under the RELIABILTY STANDARDS.
Q. Does ACSR or ACSS meet the ADVANCED TRANSMISSION TECHNOLOGIES standards?
A. No, in fact there is a question as to whether ACSR and ACSS can meet the RELIABILTY STANDARDS.
Anyway here is the actual testimony:
Q. On March 25, 2004, the Board issued a memorandum in this proceeding requesting the“parties provide an evaluation of the merits and potentials” of aluminum-composite
conductors. What is your view of the primary benefits afforded by the use of aluminum composite conductors?
A. In cases where reconductoring is desired for existing lines using existing structures,aluminum-composite core conductor may provide substantially higher current carrying capacity than can standard aluminum conductor steel reinforced (ACSR) conductor. This increased current carrying capacity may be as much as twofold and is due to the fact that the thermal expansion versus loading, and the associated increase in sag of this conductor type, is substantially less than that of ACSR.
Q. How could the improved performance of aluminum-composite core conductor be appliedto new transmission line construction in the proposed NRP?
A. For a given selected ACSR conductor size, use of aluminum-composite core conductor would result in reduced conductor sag. As a result, pole heights could be reduced providing an aesthetic benefit. For a span length on the order of 550 feet, a reduction of structure heights on the order of 4 feet may be achieved.
Q. What composite core conductor types are available?
A. We are aware of two types. One, referred to as ACCC (Aluminum Conductor Composite Core), is being marketed by Composite Technology Corporation. It has a core comprised of glass and carbon fibers bonded with a polymer resin. The other, referred to as ACCR (Aluminum Conductor Composite Reinforced), is marketed by the 3M Corporation. Its core is comprised of ceramic fiber reinforced composite wires.
Q. What is the status of the ACCC product?
A. This product is still in the relatively early stages of development. We are not aware of any significant installations of ACCC and understand that installation of the first test line is in progress. One of the manufacturer’s claims, that of reduced electromagnetic fields compared to ACSR, appears to defy the basic laws of physics. This raises questions of credibility with respect to other claims associated with this product. We are skeptical of this product and discourage its application in the NRP.
Q. What is the status of the ACCR product?
A. ACCR is more developed than ACCC, and 3M Corporation claims that a full line of hardware is available for use with ACCR. However, to date, there have been only five trial installations of ACCR by utilities. These trials are in various stages of completion. Further, the cost per unit length of ACCR is expected to be on the order of 10 times that of ACSR, and there is only one supplier. Due to the high cost and relative lack of product experience, we recommend caution regarding application of ACCR to the NRP. If considered at all, we recommend that ACCR be used only for relatively short line sections and only after due consideration to the use of other alternative conductors, as discussed below.
Q. Are you aware of other conductors types, the use of which could reduce pole heights?
A. Yes, we are aware of Aluminum Conductor Steel Supported (ACSS) conductors. With ACSS, a stranded steel core provides most of the conductor’s tensile strength. At high temperatures, the steel core supports the conductor entirely. The conductor’s thermal expansion is that of steel which is significantly less than the thermal expansion of the aluminum/steel combination of ACSR.6 While the thermal expansion of ACSS is greater than that of composite conductors, the use of ACSS achieves most of the high temperature sag reduction possible with composite conductors without the higher cost and risks associated with a new product.
Q. What is the status of the ACSS product?
A. This product has been available for some 35 years and has a wide installation base. It is available from three suppliers and its cost is estimated to be approximately 15% higher than ACSR.
Q. Beyond the cost premium, are there other disadvantages to ACSS?A. ACSS conductor has a lower tensile breaking strength than an equivalent ACSR conductor. This raises a concern given the ice loading requirements for conductors in Vermont. There are various ways to mitigate this impact of ice loading, including reduced span lengths and the use of a variation of ACSS, discussed below.
Q. What is the variation of ACSS that may alleviate the concern with ice loading?
A. A variation of ACSS, referred to as ACSS/TR, utilizes aluminum strands with trapezoidal cross sections which reduce the outside diameter of the wire for a given net cross sectional aluminum area. For a given outside diameter, ACSS/TR has a higher tensile strength and lower electrical resistance (resulting in lower losses) than ACSR. ACSS/TR comes at an additional cost premium on the order of 25% over ACSR.
Q. What is your overall recommendation regarding consideration of alternative conductors for the NRP?
A. We recommend that ACSS and ACSS/TR, for reasons including cost, number of suppliers and product maturity, be considered for situations in which pole height reductions are desirable. Before application, careful consideration should be given to the specific requirements of a given line segment.
Q. Does this conclude your testimony?
A. Yes.
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