Mitigate Sag Violations
We all got the memo – after discovering several transmission lines that violated clearance limits, NERC and FERC made it clear utilities needed to inspect their transmission lines and develop a plan to mitigate excessive conductor sag. A number of options were and are being considered which include re-tensioning, raising, modifying or replacing existing structures, derating or installing high-capacity, low-sag conductors such as ACCR, C7 or ACCC® Conductor. In many cases, high-temperature, low-sag "HTLS" conductors such as ACSS were also considered, but because their sag characteristics were similar to ACSR (both of which use conventional steel cores) they were ruled out as viable solutions.
Improve Grid Reliability & Resilience
Eliminating sag clearance violations was the logical first step. Recall the major east coast blackout of 2003. Notwithstanding telemetry calibration issues, poor communications, computer glitches and reboot failures, sag trip outages led to a cascading failure of the entire east coast grid. While each of these issues were addressed and corrected, the need to improve grid reliability and resilience has become even more clear by increasingly frequent and more severe weather events.
More recently, on the west coast, high temperatures, drought conditions, strong winds and horrific fires have wreaked havoc with local utilities and their customers who are now having to endure preemptive power outages to reduce the risk of starting additional fires. While sag is obviously a drag, it is not the only aspect of improving grid reliability and resilience. High-performance conductors are also enabling grid operators to reroute power around areas where lines are being serviced or in areas where the threat of fires or other events is anticipated, because they can carry more current – without exhibiting excessive thermal sag. Some of these conductors have also been proven to be highly resilient and resistant to cyclic load fatigue, corrosion, impact, fire and storm events.
Increase Line Capacity
Increasing line capacity is extremely important for the N-conditions described above. It is also important to our changing mix of generation resource assets. Conventional plants continue to be shut down, while renewable assets are coming online at an ever-increasing rate. The difficulties we continue to face as it relates to building new transmission lines makes it evermore appealing to find ways to increase the capacity of existing transmission lines.
High-performance conductors – supplemented by substation upgrades – can generally help double the capacity of existing lines. In 2016, for instance, American Electric Power doubled the capacity of two 120 circuit-mile 345 kV lines in the lower Rio Grande Valley by swapping out double bundled ACSR Drake size conductor with double bundled ACCC Drake size conductor. The fact that they completed this mission while the circuits remained energized won them the EEI Edison Award that year.
Improve Grid Efficiency
Discussions about 'efficiency' have generally revolved around demand-side appliances and generation resources. In spite of our nation's low D+ grid rating (as reported by the American Society of Civil Engineers in 2012 and 2017), few transmission engineers give transmission efficiency much thought, because line losses are relatively low in the U.S. and the recognized costs of losses are simply passed on to the consumer. However, when AEP upgraded their two circuits in Texas, not only did they increase line capacity to accommodate load growth, they also reduced line losses by a surprising 30 percent. Even with a relatively low "load factor," line loss reductions were estimated to save 300,000 MWh per year. At $50.00 / MW, that's $15,000,000 per year or $450,000,000 over 30 years (a simplified view).
Based on all combined sources of generation in Texas (2016), the project also reduced CO2 emissions by 200,000 metric tons – the equivalent of removing 34,000 cars from the road. Can you get your arms around this? Use a high-performance conductor, classified by some as a high-temperature, low-sag "HTLS" conductor, and reduce line losses? True story. Has anyone recently priced out a new Tesla? If my calculator was capable, I’d run some numbers on the cost of buying 34,000 of them for grins and giggles, but I'll save the trouble because most of us know where much of our electric energy still comes from. Please don't get me wrong – I just installed a 400 amp meter on my house, because I know they are coming and strongly support renewables.
Environmental Attributes
As mentioned above, the ACCC Conductor's ability to reduce line losses can translate into reduced fuel consumption and reduced emissions, or at the very least - enable an increase in clean energy delivery. While these may seem like second or third tier benefits, consider that many states have established CO2 reduction initiatives and that policy makers, regulators and governors consider these 'high-value' topics. In California, for instance, it's not unlikely that the Air Resources Board (CARB) speaks from time to time with CAISO and CPUC. It may be no coincidence that 'cleaner' projects received approval over other projects in the queue. The Asian Development Bank has recently funded various transmission projects in developing countries where high-efficiency conductors were specified and funded under economic development and climate change mitigation initiatives. Green Bond Financing is also gaining momentum here in the U.S.
Conclusion
Our industry is risk averse by nature and for good reason. However, the challenges we face today cannot be resolved using 100+ year old technology. High-performance conductors offer performance advantages that should no longer be ignored, and policy makers, regulators and project financiers are taking note.
Endnote
In 2003, CTC Global introduced the ACCC® Conductor. CTC replaced the steel core wires in conventional ACSR overhead conductors with a hybrid carbon fiber core. The carbon fiber core is ~50 percent stronger and 70 percent lighter than steel. The lighter weight structural core allows the incorporation of 28 percent more conductive aluminum without a weight or diameter penalty (using compact trapezoidal shaped strands). The carbon fiber core also exhibits a coefficient of thermal expansion about ten times less than steel which serves to mitigate thermal sag. To date, over 50,000 miles of the ACCC Conductor have been installed at over 700 projects in 50+ countries. In the United States, the ACCC Conductor has been widely deployed by Southern California Edison, American Electric Power, NV Energy and several others. For more information, please visit www.ctcglobal.com
