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The Transmission Planning Process

By Ric Austria

(This Blog presents the salient points of a presentation made to the North Carolina Utilities Commission in 2022 on the subject. A redacted version of the presentation can be found at this link. The author is Executive Principal at Pterra Consulting, and has conducted courses on Transmission Planning and related topics for over 40 years. He pioneered the concept of planning for Robustness and Flexibility, which are discussed further in this Blog.)

 

Transmission planning is changing. That is to say, it has always been changing, evolving to adapt to the changing electric supply and delivery landscape. From the early days of PURPA to deregulation to the development of energy markets to the first wind farms and on to zero emissions target portfolios, inverter-based resources, storage, offshore wind, high-voltage direct current (HVDC) transmission, distributed generation, data centers, and more, the building blocks for transmission plans have been constantly changing. In parallel, the perceptions on the role of electric energy in global commerce and livelihood, the desire for a greener energy mix, the acceptable costs for maintaining reliability and the aim for sustainability and resilience have likewise been factors for change. Furthermore, the end-game calls for electric transmission and the “ugly” structures that enable the transfer of potent energy have grown louder: that the future is in microgrids or beamed transmission, or portable energy sources, and other non-wires alternatives, and hence, that we need those towers and poles less and less, and eventually not at all. Perhaps, but not just yet, not by far. For the moment, whether that be a brief one or a longer timeframe, we still need to plan for transmission. To do so, we need to have a proper process for transmission planning, one that is appropriate for the present time to address the needs and objectives that we value today.

Recently, the prime drivers for change in the USA are federal and state mandates for improved planning, use and management of transmission systems. FERC’s initiative for an improved planning process to state mandates for various targets on solar, storage, offshore, mini-nuclear, and the like, are now necessary and important considerations in planning. (The FERC NOPR and examples from New York, New Jersey and California are discussed in more detail in the linked slide deck.)  Significant elements of these mandates, to name a few, are: “right-sizing” replacement transmission lines, consideration of advanced technologies, coordinated planning across states and regions, impact of distributed generation, unified planning models, and public policy transmission needs. These considerations introduce significant, even game-changing and paradigm-shifting, factors in developing transmission plans. However, the desired attributes and features for such plans can still be generalized into the following three key characteristics:

  1. Long-term viewpoint. Transmission lines have 40-plus years of effective lifetimes and plans need to account for at least a significant portion of that period.
  2. Plans need to provide for a future transmission grid that maximizes the desired attributes, or, if stated from the orthogonal perspective, that poses the least regret.
  3. Because the future is uncertain, the plan needs to have a built-in roadmap that provides for alternate tracks for when less expected events take place.

And yet, there is more. While not yet widely accepted, there is a growing and insistent demand to design transmission systems, not based on a capacity model but on an energy model. The capacity model for the transmission system is embodied in the so-called Umbrella Principle, which states that “if an electric grid is able to reliably withstand extreme conditions such as high peak demand, and uncustomary climate and/or market conditions, then it can reliably weather any other operating condition.” The thin membrane represented by the fabric of the umbrella defines the capacity boundary within which the grid operates reliably. The capacity model leads to transmission plans that are defined by extreme conditions of use. Energy planning, in contrast, relies on the application of advanced technology and non-wires alternatives, such as dynamic line rating, programmable storage, power flow controllers and advanced distribution management systems, among others, to mitigate extreme grid operating conditions. The least-cost objective of energy planning is thus modern technologies and programs in combination with transmission infrastructure plans. Energy-based transmission planning is starting to appear in the industry such as in the energy headroom measurements posted by New York utilities and the Energy Storage NOPR released by FERC.

Needless to say, there is much in flux in transmission planning processes. Some of the best practices that we can note are:

  • Coordinated planning involving more stakeholders, including state and local agencies, generation developers, customer groups, banks, regulatory agencies, research and development institutes, taxation authorities, etc. While not all parties can participate in the detailed simulation and modeling aspect of transmission planning, their input and oversight enable a broader perspective than the traditional centralized planning process.
  • Involvement, if not actual integration, of distribution planning. A significant portion of new and planned energy resources are smaller scale, interconnecting at distribution voltages. The issues of net metering, backfeed and upramp/downramp capacities have a significant impact on transmission systems.
  • Broader study sets. As noted earlier in this Blog, system use is changing. Even when still applying the Umbrella Principle, the number of unique conditions for grid stress has increased, necessitating more models and more simulations of future conditions.
  • Directed renewable development. Two efforts to attract the development of renewables where existing and planned transmission capacity is or will be available are: (1) renewable energy zones, or REZ, where bulk transmission capacity is planned ahead of supply availability to attract developers, and (2) hosting capacity and energy headroom which identify where transmission headroom is limited and where utilities may garner regulatory support/approval to expand the transmission to attract future developers. Directed development reduces the uncertainty of planning for the future.
  • Formalized procedures to accept advanced technologies and programs as planning components. Several are ongoing, such as FERC’s efforts to standardize dynamic line rating and utility efforts to use advanced distribution management to interconnect energy-only resources.

The link includes a sample outline for a capacity-based transmission planning process. While this is perhaps still best practice for today, it is easy to envision drastic changes to the process as the broader considerations discussed in this Blog have noted.

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Pterra at PSCAD UGM 2023

Introducing Our Principal Engineers’ Talk at PSCAD UGM 2023, Boston!

 

Join us at PSCAD UGM 2023 in Boston, where our Principal Engineers will unveil a compelling case study. A load break switch’s unexpected failure during a vital task led to an extended arcing event, triggering a single line-to-ground fault. Using PSCAD/EMTDC simulation, we examined the interrupter’s transient recovery voltage (TRV). In a restrike scenario, the transient current surged to 1000 A, and the peak line-to-ground voltage spiked to 2.20 p.u. Notably, the computed TRV reached 536 kV post-restrike, surpassing the interrupter’s 480 kV TRV capability rating.

This study highlights two key recommendations:

  1. Enhanced Operational Protocols: For interrupters without capacitive switching ratings, review and refine switching procedures.
  2. Empowering Line Charging Interruption: Explore interrupters with capacitive current interruption capabilities to handle unloaded transmission lines.

For the full slide set and deeper insights, contact us at info@pterra.us. Don’t miss this illuminating presentation shaping the future of power engineering!

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Pterra Conducts Interconnection Assessment for New York Great Lakes Wind Energy Feasibility Study

In December 2022, the New York State Energy Research and Development Authority (NYSERDA) published a report on the Great Lakes Wind (GLW) energy feasibility based on a study conducted by the National Renewable Energy Laboratory (NREL), Advisian Worley Group, Brattle Group and Pterra Consulting.  This study (link to the full report) was intended to complement the options for renewable resources such as land-based wind, solar, hydro and offshore wind that would help meet New York’s renewable energy portfolio and decarbonization goals under the New York State Climate Act.

New York State is bounded by two of the Great Lakes, Lake Erie to the west and Lake Ontario to the north. The potential for developing fixed and floating wind turbines on the lakes using both existing and emerging technologies was the focus of the feasibility study. The study examined myriad issues, including environmental, maritime, economic, and social implications of wind energy areas in these bodies of freshwater and the potential contributions of offshore GLW projects.

Pterra’s role in the study (link to interconnection report) was to conduct a feasibility assessment for potential interconnections of GLW generation with the New York Bulk Power System (NYBPS). To perform the assessment, Pterra developed power flow models to represent the NYBPS in 2030 with an assumed renewable generation buildout.

To provide a measure of interconnection capacity, the capacity headroom definition and calculation method described in recent New York State Public Service Commission orders were selected. Potential points of interconnection (POIs) on the existing NYBPS substations located within 20 miles of either the Lake Erie or Lake Ontario shoreline were initially selected for analysis. These were filtered down to a few representative POIs for more detailed analysis. (Headroom represents the potential capability for GLW to interconnect; however, it also represents the capacity that is available to any other generation resource that may want to interconnect at the same POI. The nature of the NYISO market for any new generation is competitive and GLW is expected to compete with other resource development modeling analyses to utilize the available headroom.)

Lake Erie abuts the New York counties of Erie in the north and Chautauqua in the south. For Lake Erie GLW, the available POIs showed combined capacity headroom of 270 megawatts (MW) without transmission upgrades. Applying a set of simple transmission upgrades costing some $68.8 million can increase the Lake Erie total headroom capacity by 60 MW to 330 MW.

New York State has a longer shoreline along Lake Ontario compared to Lake Erie. Several New York State counties border the lake, including Niagara, Orleans, Monroe, Wayne, Cayuga, Oswego and Jefferson. For Lake Ontario GLW, several POIs in Monroe and Oswego counties showed solo headroom capacity in the range of 850 to 1100 MW without the need for transmission upgrades. At most, there is a total headroom capacity of up to 1140 MW for the Lake Ontario POIs. The total headroom capacity may be increased by 140 MW by implementing simple upgrades costing some $236.6m. In Jefferson County, the studied POIs showed no solo headroom capacity. Simple transmission upgrades costing at least $164.5 million may open about 50 MW of headroom capacity.

Pterra’s interconnection assessment found that there is some headroom capacity on the NYBPS for which GLW can compete for the delivery of energy to the grid. In order to access the POIs with headroom, other reliability issues relating to transient voltage, stability, short circuit, deliverability, transfer capability and higher-level contingencies would also need to be considered.

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Benchmarking Phasor and EMT Models for Inverter-Based Energy Resources

By Francis Luces, Ric Austria

Power projects planning to participate in the wholesale market are required to undergo impact studies as part of the interconnection application process. The studies, as a minimum, evaluate the performance of the projects under instantaneous, steady-state and transient conditions. The timescales of phenomena and equipment studied are as illustrated in Figure 1.

In the specific case of transient studies, the impact of a proposed project on the voltage and frequency control capability of the overall grid is evaluated. Traditionally, it was sufficient to consider a timeframe of 0.5 to 10 Hz (10-100 msec) for a type of study known as transient stability. The computer models (and software, such as PSS/E and PSLF) used to conduct these studies are known as phasor-based models. These models capture phenomena limited to the target timeframe.

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Network Equivalents for the Power System Engineer

By R. Austria, M. Gutierrez, F. Luces

Very popular pre-2000, when computer processing bandwidth was at a premium and engineers had more time to put together study information on the desktop (the wooden one, not the one filled with integrated circuits), equivalencing appears to have gone the way of the calculator, the clock and the calendar. Ok, so not quite, as the smartphone does not yet have an “equivalent” function. This will have to wait until analytical programs for power system analysis are made portable. But nonetheless, today’s power engineers will more readily go for the brute force approach of “model everything” rather than take the extra time and effort of creating a simplified model.

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Technical Aspects of Battery Energy Storage Systems for Integration in Distribution Circuits in New York State

Pterra was engaged by the New York State (NYS) Department of Public Service (DPS) to provide some insight into technical issues associated with battery energy storage systems (BESS) interconnecting into distribution feeders. This work was part of ongoing support Pterra is providing to the NYSDPS on NYS Standard Interconnection Requirements (SIR) procedures.

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System Impact Study for a Proposed Transmission Interconnection Project in New York

By R. Tapia, M. Gutierrez and M. Infantado

Introduction

Independent System Operators (ISO) constantly face the challenge of assessing the impact of facility additions to the power grid. They normally require a system impact study for any proposed interconnection of a large generating plant or transmission project. The purpose of this analytical study is to determine the potential adverse impacts of the interconnection of transmission facilities to a power system and whether it would cause any of the following:

  • Post-contingency thermal overloading on transmission lines and transformers,
  • Voltage criteria violations on substations,
  • Negative impact on the dynamic response of power system facilities,
  • Degradation on the transfer limit of transmission interfaces,
  • Increase in substation short circuit current that could possibly exceed the fault duty of existing circuit breakers.

The system impact study determines the impact of the proposed project by comparing simulation results of the case with the project in service against the case without the project. If adverse impacts were to be found, appropriate solutions to mitigate the violations would be required, except for the extreme contingency assessment which is performed for information purposes on issues such as avoidance of widespread load interruptions, uncontrolled cascading, and system blackouts among others.

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A Second Retrospective

By R. Austria, R. Tapia, K. Dartawan, M. Gutierrez, M. Infantado

For a company to have made it through its 14th year is not much to crow about. After all, businesses do this all the time. For a boutique consulting company such as Pterra, we would not crow about this either, not about the fact that the company celebrated its 14th year of incorporation on June 29th, 2018.  But we would be remiss if we said we had nothing to be thankful about, for the weight of these past 14 years is carried in terms of good memories, tough challenges and the enlightening fellowship of colleagues, friends and families all of which were intrinsic to the Pterra mosaic.

We did write a review of our first 7 years (see An Anniversary) and promised to do another in 7 more years. And we are already here, almost in the blink of an eye.

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Utilizing PSCAD in Designing Detection Logic for Ground Fault Overvoltage

By Ketut Dartawan

(This topic was presented at the PSCAD Users group Meeting held in Atlanta, GA on Sept. 20-21, 2018. For the full presentation, please see this link.)

Many interconnection challenges exist when connecting photovoltaic (PV) resources to the electrical distribution grid. Various challenges on the distribution feeders are covered in some technical papers; however, one of the urgent topics – as recently mentioned by utilities and recognized by inverter manufacturers as well as the developers – is the potential for ground fault overvoltage (GFO) on sub-transmission systems feeding distribution feeders via a delta-wye transformer (see Figure 1).

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Applying IEEE Std. 519-2014 for Harmonic Distortion Analysis of a 180 MW Solar PV Installation

by  Ketut Dartawan,  Amin M. Najafabadi

Pterra is presenting a paper on the above subject at the IEEE General Meeting 2017- Chicago 16~20 July.  Abstract of the paper follows:

IEEE updated its recommended practice and requirement for harmonic control in electric power system after more than two decades. The most updated version of the standard (IEEE Std. 519-2014) revised the 1992 version and its static harmonic voltage and current limits. Unlike the 1992 and the older versions of the standard, the 2014 version introduces a newer approach which considers the stochastic nature of harmonic distortions.  Furthermore, it recommends limits based on the number of times distortions may occur. For example, for the harmonic current distortion, it recommends three limits: daily 99th percentile, weekly 99th percentile, and weekly 95th percentile values. Applying the IEEE Std. 519-2014 for planning studies and for harmonic assessment of proposed projects can be very challenging because presently there is no known commercial tool which fully considers the stochastic simulations and limits required in the standard. This paper demonstrates the approach used by the authors in applying IEEE Std. 519-2014 to a harmonic study recently performed for a 180 MW solar farm.

Index Terms- harmonic analysis, harmonic filters, solar power generation, statistical analysis, time series analysis

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