A Simple ROI Comparison of ACCC and ACSR Conductors

A 220 kV Case Study

Background:

Historically, the selection of a bare overhead transmission conductor was generally very straight forward. ‘Wires’ were selected to deliver a given amount of power from a generation resource to a load center or substation. While copper conductors are still in use for lower voltage distributions lines, the majority of transmission conductors use conductive aluminum strands wrapped around a steel core that greatly improves overall conductor strength to enable longer spans between towers or poles.

The capacity of bare overhead conductors is determined not only by the cross-sectional area of conductive aluminum but also by weather conditions that include ambient air temperature, solar radiation, windspeed and other factors.

In addition to selecting an appropriate conductor size, transmission engineers also design or select structures that can support the weight of the wires, the tensile loads and corresponding sags that are impacted by operating conditions and the weather. As conductors carry increased levels of current, their electrical resistance causes the wires to heat up which results in ‘thermal sag.’ It is imperative that the engineer considers many aspects to ensure that conductor sag does not violate safe clearances to underbuilt structures, vegetation, roads, or other objects.

While the ACCC® Conductor’s thermal stability and greater strength mitigate excessive sag and enable greater spans between fewer and/or shorter structures, and added capacity and improved efficiency offer additional benefits, the ‘per meter’ cost is generally higher than the ‘per meter’ cost of conventional steel reinforced ACSR or ACSS conductors. The purpose of this brief paper is to demonstrate how the slightly higher cost of ACCC® Conductor can be offset quickly while offering substantial benefits over the conductor’s anticipated service life.  

Scenarios & Assumptions:

Using one of five scenarios previously investigated by SCS Global Services to validate the CO₂ emission reduction attributes of ACCC® Conductor, this paper considers a 40-mile 220 kV single circuit transmission line. The assumptions used for calculations per IEEE 738 Guidelines are as follows:

Analysis:

This scenario considers performance differences between 1113 kcmil Finch size ACSR Conductor and 1447 kcmil Munich size ACCC® Conductor. Their weight and diameters are nearly equivalent. The load requirement in this scenario is 1,200 peak amps with a load factor of 50%. The maximum ampacity of ACSR is 1,266 amps at 100° C and 2,376 amps at 200° C for ACCC. Conductor temperatures at 1,200 amps are 93° ACSR and 75° C ACCC. The ACSR Conductor offers reserve capacity of 66 amps while ACCC offers 1,176 amps. It could be argued that an engineer could choose a much smaller and lighter (and less expensive) ACCC Conductor with a corresponding savings in structure cost, but in today’s world where the demand for electricity is expected to nearly double by 2050, this option will be bypassed for this analysis. If we consider a new transmission line where the cost of land, permits, structures and installation would generally be considered equal for either conductor selected, we can focus on the conductor cost and advantages alone.

The use of ACCC® Conductor in this scenario offers:

• Reduction in line losses of 14,512 MWh/year (a 30% improvement)

• An annual savings of $725,610 at $50/MWh or $1,451,220 at $100/MWh

• Line loss reduction also frees-up 1.66 MW of wasted generation capacity (~$1.6 million)

• A 30-year line loss reduction savings of $21,768,286 at $50/MWh or $43,536,572 at $10/MWh

• An annual reduction of CO₂ by 7,011 metric tons (210,317 MT over 30 years)

• Ability to deliver an additional 1,176 amps – nearly twice that of the initial 1,200 amp requirement

This 40-mile example would require ~120 miles of conductor (633,600 feet) as there are three phases (wires) on alternating current AC transmission lines. While conductor pricing can fluctuate with steel and aluminum pricing (often discounted with blanket or larger orders), consider the ACSR Finch is $2.00 per foot and ACCC Munich is 5.30 per foot. The corresponding conductor costs (without tax or delivery fees) would be $1,267,200. and $3,358,080., respectively – a $2,090,880 delta.

While a $2.1 million cost delta is not insignificant, the Western Electricity Coordinating Council reports that the cost of 220 / 230 kV transmission lines in the U.S. range from $1.5 to $2.0 million dollars per mile. On a 40-mile project, the added cost could be considered negligible - especially as many policy makers and regulators strive to “right-size” proposed transmission lines to prepare for anticipated growth. Assuming the $1.6 million generation capacity savings and/or CO₂ reduction benefits would be enjoyed by others, the added cost of using ACCC® Conductor would hit break even in 35 months based on line loss reductions alone at $50/MWh or 17.5 months at $100/MWh. If topography allowed, it might also be possible to reduce upfront structural costs and construction timeframes due to the ACCC® Conductor’s ability to span greater distances between fewer and/or shorter structures compared to steel reinforced conductors.

Looking at this example through a different lens – and assuming the overall project cost of this 40-mile line was $60 million ($1.5 million per circuit mile), the ACSR option at 1,266 max amps would equate to a $47,000 per amp project cost vs a $25,000 per amp project cost for the 2,376 amp ACCC alternative.

In any case, the additional $2.1 million investment would be quickly (if not immediately) recovered with an annual return ranging from $725,000 to $1,450,000 based on line loss reductions alone – not taking into account any additional revenue that could be gained by delivering more power over time.

For more information, please visit www.ctcglobal.com or contact [email protected]