Among the few points of agreement in a partisan Congress and the transition to cleaner energy resources is that the transmission grid needs to be enhanced. For reliability reasons, efficiency gains, the move away from fossil fuels, infrastructure investment and economic growth perspectives, many parties are advocating for increased capacity to move power in different parts of the country.
How to make the improvements is where the parties diverge. Republicans support infrastructure investments and refer to permitting delays for new power lines, the North American Electric Reliability Corp. has said more transmission is going to be needed as decarbonization steps are made, wind and solar power advocates refer to regional planning and cost allocation woes that hinder clean energy development, while others point to new technologies and regulatory hurdles.
In that latter group are a collection of entities in support of dynamic line ratings (DLR) that filed comments on a notice of proposed rulemaking (NOPR) from FERC about possible transmission line rating changes. Companies supporting increased use of DLR point to reliability improvements, lower costs to consumers from transmission congestion, resilience tied to weather events – since DLR factors in line conditions constantly rather than static assessments generally in use today — and more accurate assessments of where transmission enhancements may be needed in the future.
Transmission investment in new lines is needed, but hard to gain approval and takes years to complete, with multiple agencies involved. Current technologies can improve the capacity and use of existing facilities, which is why DLR and small steps are just as important as expanding the grid through new transmission, said Rob Gramlich, executive director of the WATT Coalition and president of Grid Strategies LLC.
The bulk power system is undergoing such changes from generation resources that “we’re going to need all of these things,” Gramlich said in a March 24 interview.
Grid Strategies supports decarbonization plans and increased use of clean energy resources, while the WATT Coalition is a group of companies including LineVision Inc. and SmartWires advocating for technologies to improve transmission reliability and efficiency.
Cost allocation for new transmission lines is a huge factor and a near-constant sticking point because many people benefit from them but nobody wants to pay for them. Assigning costs to various market participants is difficult because while everyone supports a grid expansion “they want their neighbor to pay for it,” Gramlich said.
Which is where increased use of DLR, high voltage direct current (HVDC) lines, changes in cost assignment factors for state regulators and other steps to wring more efficiency out of the transmission grid come into play, Gramlich and others have said. During a March 16 online event sponsored by Americans for a Clean Energy Grid, Liza Reed of the Niskanen Center and Michael Pesin of the Department of Energy (DOE) noted how the transformation of the power grid needs to be reflected in regulatory changes that enable, rather than hinder, new technologies.
Transmission capacity improvements means more than building new power lines, said Pesin, deputy secretary for the advanced grid in the research and development arm of DOE’s Office of Electricity. Since increased use of distributed energy resources results in a different paradigm than contemplated in current regulatory structures, changes are needed to reach the grid of the future, Pesin said.
HVDC lines are not cheap, but converting existing alternating current lines to HVDC lines can gain 3.5 times the transfer capacity on the same land footprint, added Reed, research manager for low carbon technology policy at the Niskanen Center. HVDC lines have less power loss over long distances and it is an existing technology that can be enmeshed in current grid corridors “to push a lot more current through” transmission lines, Reed said.
Because cost/benefit analyses do not always capture long-term benefits from such changes, “we need to start quantifying things like wildfires and resilience” in the regulatory reviews for changes to the grid, Reed said. Certain technologies may have higher up-front costs, but a stronger, more stable grid will pay off in broader economic benefits. Carrying that message to state regulators and Congress can help them understand the changes needed, she said.
In its comments on the line ratings NOPR at FERC, the WATT Coalition pointed out that DOE did a study on DLR in 2014 and FERC has a separate docket (RM20-10) on investment incentives for grid-enhancing technologies. Asserting that FERC “proposed a set of unworkable incentives,” the WATT Coalition agreed with industrial customers that the Commission should explore ways to increase transmission owners’ incentive to use DLRs, since those owners may have no financial reason to improve operational efficiency.
Competitive generation owners are generally in favor of DLR and improved line ratings to increase power flows on existing lines, but transmission owners are hesitant to make changes because they have no incentive to do so, Gramlich said during the interview.
That is clear in other comments filed at FERC, where the recent deadline resulted in more than 50 companies and groups submitting their views. Transmission owners in the Midcontinent Independent System Operator (MISO) support certain aspects of using ambient-adjusted ratings (AAR) where benefits outweigh the costs, and raised concerns about broad use of DLR or widespread use of AAR. Directing transmission owners to use AAR in day-ahead and long-term analyses “is overly broad and will not yield benefits in MISO that are sufficient to justify the added cost, effort, complexity and operational challenges associated with the proposal,” the MISO transmission owners said.
Instead of the proposals laid out in the NOPR, FERC should move to guidelines and allow regional flexibility on the use of AAR, with alternative compliance approaches, the MISO transmission owners said.
Use of AAR or DLR can enhance transmission capabilities at certain times, but they are not a substitute for long-term transmission planning and investment, said the MISO transmission owners, which include investor-owned utilities, municipal utilities, cooperatives and independent transmission companies.
“Implementing adjustable line ratings, whether in the more limited, targeted, and net-beneficial fashion advocated in these comments or in the broad scope proposed in the NOPR, will not address the long-term needs of the transmission system brought about by a changing resource mix and evolving demands,” they said.
The NOPR was issued in November of 2020 to improve the accuracy and transparency of transmission line ratings. FERC staff and commissioners noted how transmission congestion could be lessened for the benefit of consumers.
Existing transmission line ratings are seasonal or static, with conservative assumptions about temperatures and conditions that may not accurately reflect the transfer capability of power lines, FERC explained Making line ratings more accurate is a worthy goal to ensure the power grid is used to its fullest capability, with use of AAR suggested and comments sought on DLR. AAR does not require changes on the lines themselves, while DLR is not widely used due to costs associated with placing sensors on lines to measure wind speed and temperatures.
Several utilities have tested and are testing DLR on congested lines, while the transmission owners in MISO pointed out the grid operator’s effort to use AAR where beneficial.
In its comments, NERC did not address DLR and referred to reliability standards on line ratings such as AAR. NERC’s reliability standards would not preclude the use of AAR in developing more accurate line ratings, but there may be issues around implementation of FERC’s proposed rule that require careful attention, NERC said.
Additional clarity is needed on several subjects, NERC said. Those include: whether ISOs would be required to coordinate ambient temperature methods since temperatures used on tie lines between regions could differ; what would happen if there is a disagreement among entities on ratings or methodologies; what temperature settings should be used for AAR, with high temperatures potentially limiting transmission capacity and low temperatures possible exposing the grid to reliability risks; how entities should reconcile AAR for planning and calculating available transmission capacity; and considerations for using AAR across long transmission lines that span multiple climates.
The NOPR appropriately recognizes that some transmission facilities are not affected by changes in ambient air temperature and would be exempt from AAR implementation, the Edison Electric Institute noted. While AAR is effective in optimizing transmission capacity in certain areas, FERC’s proposal to require AAR nationwide “would not provide equivalent improvements in efficiency across all facilities,” EEI told FERC. Universal application of a specific practice or operational requirement for line ratings eliminates the flexibility of transmission owners to address grid operations under unique circumstances, the investor-owned utility group said.
Though implementation of AARs has yielded efficiencies when used in real-time and day-ahead operations in some areas, the benefits of AARs are not necessarily the same” for every transmission owner and their use should not be required outside of where they exist currently, EEI said.
A similar view was provided on DLR, with EEI suggesting FERC should allow use when the costs are justified, but allowing the transmission owner to make that determination.
“Separately, the Commission should take into consideration that as the number of sensors and other interconnecting points needed along the grid to implement DLRs or other transmission line ratings increase significantly, so does the opportunity for cyber-security attacks,” EEI added. The risks of a cyber intrusion using such technologies and the associated costs of any cyber incident must be measured against any perceived benefits, EEI said.
Plenty of transmission congestion studies, including in MISO, show that more accurate line ratings bring benefits aside from using DLR, the WATT Coalition said.
The grid reliability improvements and cost savings are both compelling reasons for changes to be made, Gramlich said. The WATT Coalition is not advocating use of DLR everywhere, but recommends where grid congestion and conditions make sense, he noted.
Wind speed is the most significant factor affecting transmission line capacity, with much greater impact than temperature, according to the group’s comments. DLR takes wind speed and associated conductor cooling impacts into account to better inform operations, while AAR does not. The group said modest wind speed changes lead to nearly a 50%increase in capacity while temperature changes of more than 20 degrees Fahrenheit lead to slightly more than a 10% change in capacity.
By Tom Tiernan email@example.com