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Suggested Citation:"4 Models for Transmission Planning." National Academies of Sciences, Engineering, and Medicine. 2020. Models to Inform Planning for the Future of Electric Power in the United States: Proceedings of a Workshop. Washington, DC: The National Academies Press. doi: 10.17226/25880.
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4

Models for Transmission Planning

Anjan Bose, Washington State University, introduced the second session with an overview of some significant recent shifts seen in transmission planning.

First, he said that the United States and Canada have slowed their pace of innovation in transmission technologies, while many other countries, such as Brazil, China, and India, are continuing to innovate in this space in order to keep up with their growing demands. In addition, it is now clear that the increasing interaction between transmission and distribution must be incorporated into modeling. “It used to be almost completely separate,” Bose said. “Transmission planners never had to actually talk to distribution planners, and distribution planners never had to talk to transmission planners, and we did just fine. And now, of course, everything is changing.” Last, Bose stressed the importance of modeling the increasing use of system control and protection across transmission and distribution in both design and planning.

The speakers were Joseph Eto, Lawrence Berkeley National Laboratory (LBNL); Tom Overbye, Texas A&M University and PowerWorld Corporation; Douglas Welsh, General Electric (GE); Branden Sudduth, Western Electricity Coordinating Council (WECC); and Amos Ang, Southern California Edison (SCE). Speakers and participants discussed challenges that the industry faces in translating academic research and models to inform decision making; the vast range of scenarios and time scales that are accounted for in transmission system planning; and priorities for improving models.

Suggested Citation:"4 Models for Transmission Planning." National Academies of Sciences, Engineering, and Medicine. 2020. Models to Inform Planning for the Future of Electric Power in the United States: Proceedings of a Workshop. Washington, DC: The National Academies Press. doi: 10.17226/25880.
×

JOSEPH ETO, LAWRENCE BERKELEY NATIONAL LABORATORY

Eto, a staff scientist at LBNL, set the stage for understanding how the electric power industry uses modeling in transmission system planning.

As the ultimate “just-in-time” delivery product, electricity supply and demand must be carefully managed throughout North America’s highly interconnected, interdependent grid. “This real-time balancing of supply and demand really drives everything that’s going on in this industry,” Eto said. “Things happen in the blink of an eye.” A lack of adequate preparation, he added, can lead to blackouts.

The industry is continuously balancing economically efficient dispatch of generation to minimize the costs of production against the extra cost of maintaining reserves required to respond to problems that arise in real time. Advance planning on multiple time scales, Eto said, is central to establishing this balance.

Managing the reliability of the electric transmission system involves managing resources economically over multiple time scales, from microseconds to decades (Figure 4.1). While the most dire problems can emerge in the blink of an eye, the suite of solutions required to address them while at the same time minimizing the total costs of electricity requires analyses appropriate to each time scale. For example, steady-state and dynamic power flow modeling tools are needed to study and plan for

Image
FIGURE 4.1 Distinct classes of planning tools are used to support operations over different time scales. SOURCE: Courtesy of Alexandra von Meier and Joseph Eto, Lawrence Berkeley National Laboratory.
Suggested Citation:"4 Models for Transmission Planning." National Academies of Sciences, Engineering, and Medicine. 2020. Models to Inform Planning for the Future of Electric Power in the United States: Proceedings of a Workshop. Washington, DC: The National Academies Press. doi: 10.17226/25880.
×

system stability over shorter time frames; when problems occur, real-time contingency analysis and short-term forecasting are used to anticipate upcoming challenges and the requirements of the solutions required to address them. For longer time frames, day-ahead scheduling and production cost simulation are used in order to optimize investments and minimize transmission loss.

The most significant challenges for transmission planning, according to Eto, are the changing resource mix, the challenges associated with incorporating new inverter-based generation technologies, modeling for resource variability, changing market structure and behavior, and understanding long-term impacts of new public policies and technologies. Transmission planning increasingly also requires careful investigation of the interplay between electric power and other sectors, and must also incorporate new factors, such as integrated transmission-distribution planning and cybersecurity, Eto said.

TOM OVERBYE, TEXAS A&M UNIVERSITY AND POWERWORLD CORPORATION

As a professor at Texas A&M University and a software engineer at PowerWorld, Overbye spoke to the need to bridge academia and industry to address key challenges in electric power system planning. This involves systemic changes to align incentives and rewards, as well as practical steps to find the right approaches to address the right questions. “How do we effectively leverage the broad community of researchers and practitioners? There is great research coming out from lots of different fields that we can use in the power system industry. But … a lot of times in the academic research community, they’re focused on solving the wrong problems,” Overbye said. “They fit the system to what they can easily solve.”

One reason academic research is not always relevant to real-world problems, he said, is that academics are forced to use small-scale or simplified grids, because actual grid details are protected information. While it is true that all models are an approximation of reality, overly simplified models cannot produce useful results.

To overcome that problem, Overbye develops synthetic grids,1 which are fictional, yet highly realistic, large-scale representations of transmission and distribution grids, designed to be used for industry-applicable academic research (Figure 4.2). In addition to their benefits for research and development, synthetic grids also offer the next generation of power

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1 Available at Texas A&M University Engineering, “Electric Grid Test Case Repository,” https://electricgrids.engr.tamu.edu/.

Suggested Citation:"4 Models for Transmission Planning." National Academies of Sciences, Engineering, and Medicine. 2020. Models to Inform Planning for the Future of Electric Power in the United States: Proceedings of a Workshop. Washington, DC: The National Academies Press. doi: 10.17226/25880.
×
Image
FIGURE 4.2 Large-scale synthetic grid models are publicly available for research, development, and training purposes. SOURCE: Courtesy of Tom Overbye, Texas A&M University.

engineering operators an opportunity to practice on real power management unit modeling data. While available transmission and distribution synthetic grids are separated, Overbye said that future synthetic systems will be more integrated and include renewable energy variations and other innovations.

Another way to unite researchers with practitioners is to change publishing incentives, Overbye noted. He argued that papers that address the grid’s real problems are rarely published because researchers, not engineers, run journals. More widespread support for publications focused on solving real engineering problems would better facilitate meaningful exchange between the two communities and enhance future solutions.

DOUGLAS WELSH, GENERAL ELECTRIC

Welsh, managing director of software at GE Energy Consulting, oversees multiple modeling products, including GE MAPS for production simulation, GE MARS for resource adequacy evaluation, and Positive Sequence Load Flow (PSLF) software to analyze system behavior, steady-state power flow, short circuit, and dynamic stability. He described several challenges to transmission planning and also suggested solutions.

The increased use of inverter-based resources, such as wind and solar storage equipment, creates multiple challenges for transmission planning. First, Welsh said, it can weaken the grid and create instability, especially

Suggested Citation:"4 Models for Transmission Planning." National Academies of Sciences, Engineering, and Medicine. 2020. Models to Inform Planning for the Future of Electric Power in the United States: Proceedings of a Workshop. Washington, DC: The National Academies Press. doi: 10.17226/25880.
×

in more isolated areas. In addition, those components need to be modeled in microseconds, but today’s transient stability models can reach only millisecond resolution. Also, inverter-based, variable-speed drives are not standard, and that makes it difficult to create generic equipment models, leading to potential inaccurate modeling results. There are also issues in modeling composite versions of the distribution system at the transmission level, because of the wide range of inverters used for distributed generation, and inadequate information about the location of these within the distribution system.

Another challenge is that if the United States, like China and Europe, installs high-voltage direct current grids, it will be difficult to integrate them with existing alternating current grids and models. Last, Welsh noted that the increase in distribution-side generation has made it significantly more difficult to predict and simulate power flow, stability, and reliability to ensure adequate resources, and that this trend implies the need for more probabilistic modeling in the future.

One potential solution, Welsh suggested, is to expand detailed electromagnetic transient (EMT) modeling, used in weaker parts of the grid, to include those stronger portions. There may also be a “middle ground” for incorporating EMT-like models directly into traditional transient stability simulations. Another solution being tried in some cases could be a co-simulation of transmission and distribution models, for example, to support unbalanced fault analysis.

BRANDEN SUDDUTH, WESTERN ELECTRICITY COORDINATING COUNCIL

Sudduth is vice president of reliability planning and performance analysis at WECC, the regional entity responsible for bulk power system reliability in the Western Interconnection. WECC uses models to perform reliability and economic analyses, with a focus on reliability impacts at an interconnection-wide perspective. WECC shares its transmission planning and production cost models with industry for planning studies, works with stakeholders to model and address industry’s reliability needs, and works closely with vendors to develop model structures for new technologies.

WECC faces multiple modeling challenges. First, the rapid pace of change has transformed the slow, careful practice of modeling a new transmission line or resource into a race to quickly model the impacts of a broad array of new equipment on the interconnected system. In the past, Sudduth noted, it was feasible to take an existing system model, plug a new line or resource into it, and run multiple simulations until the incremental impacts of adding a new facility could be understood. “Today, we

Suggested Citation:"4 Models for Transmission Planning." National Academies of Sciences, Engineering, and Medicine. 2020. Models to Inform Planning for the Future of Electric Power in the United States: Proceedings of a Workshop. Washington, DC: The National Academies Press. doi: 10.17226/25880.
×

really don’t have that luxury because the system is changing so quickly,” he said. Another challenge, he said, is that the changing resource mix creates the potential for stress conditions to occur at any time of day, not just during periods of extremely high or extremely low loads, as was assumed in the past.

Dealing with the interplay between different interdependent industries (e.g., gas, electric, water) and models is an overarching challenge. To overcome this problem, WECC recently studied the interdependence between the natural gas and electric subsectors. Sudduth also stressed the need to better link transmission, distribution, and operations models. “We would encourage, especially the program vendors out there, to continue to identify ways to link these models together,” Sudduth said.

Learning the deficiencies of new technologies before they cause system disturbances is another challenge. The 2016 Blue Cut fire in California created unexpected periods of momentary cessation for certain inverter-based resources, which were previously unknown and so not incorporated into the models at the time.

A final challenge, Sudduth said, is ensuring that the data used in bulk electric system modeling—typically collected from a variety of sources including transmission planners, planning coordinators, and nontraditional entities such as load serving entities that have information on rooftop solar panels—are as accurate as possible. “These models are really only as good as the data that we put into them,” he noted. “It becomes critical, as we develop these really robust transmission system models, that we’re getting accurate data, especially for existing system facilities.”

AMOS ANG, SOUTHERN CALIFORNIA EDISON

Ang, power system planner at SCE, described how SCE uses models to identify, test, and solve transmission issues and to understand impacts from larger system changes. “The two key issues that we are tasked [with], from the transmission planning perspective, is to be able to identify the issues before they happen, and [to] create solutions and fixes in place before these issues arise,” Ang said.

SCE relies on modeling to ensure safe, reliable, clean, and affordable power to its customers, he said. Models are also necessary to justify new projects to the California Public Utilities Commission (CPUC). Each model requires different data and assumptions to generate results that inform changes such as upgrading or adding a new line, increasing generation, or installing voltage support.

Key challenges that SCE faces include modeling for inverter-based resources such as wind, solar, and batteries; poor data quality; the inability to deal with a large volume of data; and lack of regulatory acceptance

Suggested Citation:"4 Models for Transmission Planning." National Academies of Sciences, Engineering, and Medicine. 2020. Models to Inform Planning for the Future of Electric Power in the United States: Proceedings of a Workshop. Washington, DC: The National Academies Press. doi: 10.17226/25880.
×

of model results. Further compounding these challenges, Ang acknowledged the perennial challenge of responding to constant technological and political change.

Ang offered several suggestions to improve modeling. First, he said it is important to have better means to translate resource plan capabilities into the models, while still ensuring accuracy. He also stressed the need for hybrid models to identify the interactions between the different modeling types, as well as better tools to analyze and verify modeling outputs.

DISCUSSION

Following the speakers’ remarks, Bose moderated a discussion session that covered the importance of incorporating high-performance computing (HPC) and other technologies; safety, reliability, and resiliency concerns; and improving models through accessibility and validation.

HPC and Other Technologies

The speakers were asked whether utilities were pursuing real-time digital simulators, cloud computing, data analytics, and other HPC technology to enhance electricity infrastructure modeling. “How do we take advantage of amazing developments, in terms of the really low cost to computing and big data analytics?” one participant asked. Welsh replied that GE, as a large company, had the resources to incorporate HPC into several of its models, and has also linked models to improve external optimization via programming languages and scripts. GE also encourages licensees to adopt HPC technologies, although he recognized that there are challenges to overcome, such as algorithm or contingency parallelization and the need to ensure that results are searchable, able to be manipulated, and linkable to other models.

Overbye expressed his belief that modeling will move to the cloud, partly to reduce costs. Modeling the increasing number of individual devices, providing continual updates and support, and testing models is very expensive, he noted. Roger Dugan, EPRI, pointed out that certain models discussed by the speakers, such as PSLF, do not reveal certain technological limitations for energizing the transmission grid from distributed energy resources (DERs) for most American substations because the models are balanced positive sequence.

Safety, Reliability, and Resiliency

Morgan asked about reemphasizing safety. Ang stressed that SCE was focused on both personnel and overall system safety, checking

Suggested Citation:"4 Models for Transmission Planning." National Academies of Sciences, Engineering, and Medicine. 2020. Models to Inform Planning for the Future of Electric Power in the United States: Proceedings of a Workshop. Washington, DC: The National Academies Press. doi: 10.17226/25880.
×

every change for safety and reliability concerns. Sudduth added that he recognizes the importance of public safety impacts from natural disasters and understands that sometimes it may be necessary to sacrifice reliability to preserve public safety—for example, in the case of reducing wildfire risk.

Eto expressed his belief that it is appropriate to increase focus on and support for public policies that address electricity reliability today. Currently, he argued, the electric power industry tends to increase its focus on reliability innovations only in the aftermath of a disaster. Ang added that public policy could drive investment in renewable energy if it were balanced with financial incentives.

A participant asked if current models accounted for nonwire alternatives (NWAs). Ang replied that the CPUC has concluded that until NWAs are cost-effective, there will not be sufficient use, and therefore sufficient data, for accurate modeling. Eto added that NWAs also face an institutional challenge because different sets of decision makers are involved in demand-side planning and reliability planning, and each has its own priorities.

Another participant described how recent energy disasters demonstrated the importance of situational awareness and integration between the electric power and oil and gas systems. The participant asked whether WECC had the right tools to deal with similar events. Sudduth answered that bulk electric system (BES) reliability is WECC’s primary objective, but it does not have oversight authority over smaller facilities or natural gas systems, even though their operations impact the BES. In this context, WECC focuses on identifying risks and collaborating with other entities to mitigate them.

Overbye also noted that situational awareness is crucial in order to correctly interpret the results of complex models. In his view, the “art” of interpreting models to inform engineering and design is often overlooked in favor of the science of engineering principles and equations.

Bose asked the speakers to discuss resiliency, particularly in the context of disasters such as wildfires. Ang replied that distribution systems are studied for resiliency, and California has multiple procedures in place to protect distribution systems in a disaster. Transmissions systems, which are less susceptible to fires, are already built for resiliency, although other challenges such as hurricanes or earthquakes could create problems. A new organization has been tasked with studying the system’s resiliency and will share its work soon, he added.

Another participant asked about the degree to which transmission planners’ and other decision makers’ investment decisions maximize societal benefits. Eto replied that large transmission projects require large financial investments. Public policies can directly influence the

Suggested Citation:"4 Models for Transmission Planning." National Academies of Sciences, Engineering, and Medicine. 2020. Models to Inform Planning for the Future of Electric Power in the United States: Proceedings of a Workshop. Washington, DC: The National Academies Press. doi: 10.17226/25880.
×

cost-effectiveness of these investments and hence help align them with societal benefits. He pointed out that the United States has substantially increased investment in transmission construction recently, driven largely by recent policy changes that increased the return on investment that transmission developers could earn on new construction.

Improving Models Through Accessibility and Validation

Asked if models could be made more accessible in order to widen the number and diversity of their users, Welsh agreed that was a good idea, and noted that some researchers are publishing models using standard application programming interfaces (APIs) for this reason. Sudduth added that WECC does share its modeling data sets, but does not itself use outside models unless they are cross-compatible with multiple vendor formats, such as GE PSLF and Siemens PSS/E.

Ang noted that SCE offers access to its models, and also hosts a model validation workgroup, where one data set is entered into different models to compare results. Welsh noted that GE has been more willing to open up some of its models’ inner workings—for example, in model validation working groups—and also has an internal standardization process for validation.

Bose agreed that it is helpful to use the same data in different models for validation purposes, but stressed that it is more important that models agree with what happens in the real world. Overbye also noted that most models do have extensive validation standards and requirements, but a challenge to making them open is that many models use protected grid information that cannot be made public.

While recognizing that the vendor model code may never be fully open, a participant asked if open source tools could nonetheless help to improve modeling accuracy. Overbye replied that companies like GE and PowerWorld will never go fully open source, but noted that open source tools like MATPOWER and OpenDSS are widely used. Ang added that data translation and fidelity is a challenge with open source tools, and while WECC can translate data via three separate platforms (PSLF, PSS/E, and PowerWorld), having just one would be better. Sudduth noted that in his experience vendors are often willing to translate data between different vendor formats in order to ensure that models can be shared between various entities.

Wrapping up, Morgan asked the speakers to share suggestions for the committee’s report. Overbye urged the committee to address whether user-defined models, where the software is first written by a user and then entered into an integrated system, should be pursued. Welsh wondered if existing models, some of which are very old, are properly understood by

Suggested Citation:"4 Models for Transmission Planning." National Academies of Sciences, Engineering, and Medicine. 2020. Models to Inform Planning for the Future of Electric Power in the United States: Proceedings of a Workshop. Washington, DC: The National Academies Press. doi: 10.17226/25880.
×

those currently using them. Last, Bose pointed out that any new simulation tool should be designed to address a real problem, as opposed to a mere reworking of existing tools that only approximate the behavior of new technologies.

Suggested Citation:"4 Models for Transmission Planning." National Academies of Sciences, Engineering, and Medicine. 2020. Models to Inform Planning for the Future of Electric Power in the United States: Proceedings of a Workshop. Washington, DC: The National Academies Press. doi: 10.17226/25880.
×
Page 31
Suggested Citation:"4 Models for Transmission Planning." National Academies of Sciences, Engineering, and Medicine. 2020. Models to Inform Planning for the Future of Electric Power in the United States: Proceedings of a Workshop. Washington, DC: The National Academies Press. doi: 10.17226/25880.
×
Page 32
Suggested Citation:"4 Models for Transmission Planning." National Academies of Sciences, Engineering, and Medicine. 2020. Models to Inform Planning for the Future of Electric Power in the United States: Proceedings of a Workshop. Washington, DC: The National Academies Press. doi: 10.17226/25880.
×
Page 33
Suggested Citation:"4 Models for Transmission Planning." National Academies of Sciences, Engineering, and Medicine. 2020. Models to Inform Planning for the Future of Electric Power in the United States: Proceedings of a Workshop. Washington, DC: The National Academies Press. doi: 10.17226/25880.
×
Page 34
Suggested Citation:"4 Models for Transmission Planning." National Academies of Sciences, Engineering, and Medicine. 2020. Models to Inform Planning for the Future of Electric Power in the United States: Proceedings of a Workshop. Washington, DC: The National Academies Press. doi: 10.17226/25880.
×
Page 35
Suggested Citation:"4 Models for Transmission Planning." National Academies of Sciences, Engineering, and Medicine. 2020. Models to Inform Planning for the Future of Electric Power in the United States: Proceedings of a Workshop. Washington, DC: The National Academies Press. doi: 10.17226/25880.
×
Page 36
Suggested Citation:"4 Models for Transmission Planning." National Academies of Sciences, Engineering, and Medicine. 2020. Models to Inform Planning for the Future of Electric Power in the United States: Proceedings of a Workshop. Washington, DC: The National Academies Press. doi: 10.17226/25880.
×
Page 37
Suggested Citation:"4 Models for Transmission Planning." National Academies of Sciences, Engineering, and Medicine. 2020. Models to Inform Planning for the Future of Electric Power in the United States: Proceedings of a Workshop. Washington, DC: The National Academies Press. doi: 10.17226/25880.
×
Page 38
Suggested Citation:"4 Models for Transmission Planning." National Academies of Sciences, Engineering, and Medicine. 2020. Models to Inform Planning for the Future of Electric Power in the United States: Proceedings of a Workshop. Washington, DC: The National Academies Press. doi: 10.17226/25880.
×
Page 39
Suggested Citation:"4 Models for Transmission Planning." National Academies of Sciences, Engineering, and Medicine. 2020. Models to Inform Planning for the Future of Electric Power in the United States: Proceedings of a Workshop. Washington, DC: The National Academies Press. doi: 10.17226/25880.
×
Page 40
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Models to Inform Planning for the Future of Electric Power in the United States: Proceedings of a Workshop Get This Book
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Providing a reliable and resilient supply of electric power to communities across the United States has always posed a complex challenge. Utilities must support daily operations to serve a diverse array of customers across a heterogeneous landscape while simultaneously investing in infrastructure to meet future needs, all while juggling an enormous array of competing priorities influenced by costs, capabilities, environmental and social impacts, regulatory requirements, and consumer preferences. A rapid pace of change in technologies, policies and priorities, and consumer needs and behaviors has further compounded this challenge in recent years.

The National Academies of Sciences, Engineering, and Medicine convened a workshop on February 3, 2020 to explore strategies for incorporating new technologies, planning and operating strategies, business models, and architectures in the U.S. electric power system. Speakers and participants from industry, government, and academia discussed available models for long-term transmission and distribution planning, as well as the broader context of how these models are used and future opportunities and needs. This publication summarizes the presentations and discussions from the workshop.

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