Planning Criteria, Assessment Practices and Tools

New June 7, 2021 – Updated Planning Criteria (21.1): ATC’s updated Planning Criteria document (21.1) can be found here. Changes include clarifying ATC’s generator power factor requirements.

New May 5, 2021  – Updated Planning Criteria (version 21):  ATC’s updated Planning Criteria document (21) can be found here. Removed old footnote 1 related to emergency ratings. Specified generators for which stability criteria applies. Replaced SPS with RAS. Effective date April 20, 2021.

New May 5, 2021 – Updated Planning Assessment Practices (version 21):  ATC’s updated Planning Assessment Practices document (21) can be found here. Removed old Planning Criteria footnote 1 implications related to emergency thermal ratings. Identified to which generators stability criteria applies. Effective date April 20, 2021.

New November 13, 2020  – Updated Planning Criteria (20.2):  ATC’s updated Planning Criteria document (20.2) can be found here. Changes include updates revising the voltage stability margin and clarifying margins for expected clearing time.

New November 5, 2020 – Updated Planning Assessment Practices (20.1):  ATC’s updated Planning Assessment Practices document (20.1) can be found here. Changes include updating section 12.9 to clarify the voltage stability margin definition.

The planning criteria ATC used in this 2020 10-Year Assessment is documented in: Planning Criteria, version 20 and Planning Assessment Practices, version 20. 

Planning Criteria

We employ various system planning criteria to plan, design, build and operate our transmission system in a safe, reliable and economic manner to meet the needs of our customers while maintaining compliance with North American Electric Reliability Corporation (NERC) standards. We apply these criteria to the transmission system operated by American Transmission Co., at 69,000-volts and above.

At ATC’s discretion these criteria may be revised at any time. Factors driving revisions might include new system conditions, new technologies, new operating procedures, extraordinary events, safety issues, operation issues, maintenance issues, customer requests, changes in industry standards, changes in regulatory requirements or changes in regional entity or NERC requirements.

Planning Assessment Practices

ATC generally subscribes to the zone approach to transmission planning assessments using a multi-level planning concept. Diagrams of the planning zones for which plans have been developed by ATC are a part of our annual 10-Year Assessment.

The concept behind the zone approach to transmission planning is to develop plans that consider all of the needs, limitations and developments within each zone and develop an overall plan for the zone (that is, a plan that emphasizes projects that serve multiple purposes or solves multiple limitations within the zone).

In addition, ATC’s transmission planning philosophies incorporate the concept of multi-level transmission planning. When carrying out a comprehensive transmission planning process, consideration must be given not only to individual transmission facility limits, zone limitations and ATC-wide limitations, but also to plans of other transmission owners. Solutions for limitations identified via planning activities within each level are vetted against those in adjacent levels until the most effective overall comprehensive plan is developed. ATC’s planning process will continue to develop the first three levels (individual, zone, ATC-wide). When assessing regional needs, ATC is participating with other Transmission Owners, such as ComEd, Dairyland Power Cooperative, Xcel Energy and ITC Holdings Corp., who are within or may be affected by MISO territory.

ATC employs the long-standing practice of using power flow (steady-state) analyses to identify system limitations and to evaluate alternative mitigation measures. ATC identifies limitations by simulating non-simultaneous and select concurrent facility outages that include line, transformer, bus section, reactive power and generator facilities. ATC may implement operating guides, such as opening lines and bus sections, to mitigate limitations (e.g., overloads and low voltages) during extreme flow conditions.

ATC also conducts dynamic stability analyses within each of its zones to assess the ability of its system to withstand the dynamics of power system disturbances. Many of these analyses are conducted in conjunction with proposed generation interconnections. In addition to generation connection studies, other analyses are conducted to assess dynamic or voltage stability performance.

ATC develops transmission projects to address appropriate congestion issues in its footprint and beyond. ATC uses the PROMOD software to analyze congestion across the ATC footprint and surrounding systems and develops projects that will relieve the congestion.

Further, ATC works with neighboring transmission owners, stakeholders and MISO to develop transmission projects that provide multiple benefits including reliability, economic and public policy benefits. These projects are often more strategic and regional in nature to help provide benefits to multiple areas as well as maintain reliability in the ATC footprint well into the future. These projects are evaluated using traditional reliability planning tools, PROMOD for economic benefits and a combination of traditional first contingency incremental transfer capability (FCITC) analysis and economic analysis to quantify their public policy benefits.

As part of MISO, ATC participates in the MISO Transmission Expansion Plan (MTEP) process. ATC participates actively in all portions of MISO’s planning efforts such as regional and economic study efforts and development of the MTEP, including numerous committees and task forces.

ATC solicits public and other stakeholder input to identify ultimate solutions through its iterative planning process. Potential solutions listed in this assessment may be modified and further developed to address the specific needs identified by all stakeholders. The solutions selected to address the needs and limitations identified will reflect the input of transmission planning process stakeholders, including customers, state and local officials and the public and will be coordinated with other planning processes, to the extent possible.

Specific opportunities for public and stakeholder participation in the planning process are provided in accordance with ATC’s portion of the MISO tariff, Attachment FF – ATCLLC. In particular, the MISO tariff, approved by FERC, addresses portions of FERC Orders 890 and 1000 calling for open, inclusive and transparent planning processes. Attachment FF – ATCLLC coverage includes planning processes and functions as well as opportunities for stakeholders to participate. The planning processes and functions include:

  1. Network adequacy planning
  2. Economic project planning
  3. Generation-transmission interconnections
  4. Transmission-distribution interconnections
  5. Transmission-transmission interconnections
  6. Transmission service requests
  7. Public policy requirements

Tariff provisions include opportunities for stakeholders to provide input to the planning processes, such as suggesting assumptions and projects, reviewing interim results, and examining final results.

ATC participates in regional transmission assessments conducted by the Reliability First (RF) Transmission Performance Subcommittee (TPS), the NERC ERAG Reliability Assessments and MISO Reliability Assessments.

In addition to those listed in its planning criteria, ATC considers other factors in its transmission planning process.

Planning tools

Our planning engineers frequently use the following computer applications to simulate the impact of potential future events on the transmission system. The same applications are used to determine how proposed solutions would address any identified adverse impacts. 

Hitachi ABB Power Grids' PROMODpredicts the cost of producing energy to serve customers.
Power Analytics Software, Inc.'s PROMOD Analysis Tool (PAT)post-processing analytics of PROMOD results
PowerGem's TARAcalculates linear (DC) and non-linear (AC) power flow, performs N-1/N-1-1 reliability analysis, calculates transfer limits, determines preventive and corrective dispatch
Siemens' (PTI) PSS/Ecalculates static and dynamic power flows
PowerTech's VSAT/TSAT/PSAT/SSATVSAT calculates the capability of the system to transfer power from one area to another while respecting voltage limitations. TSAT assesses the dynamic behavior of the system under specified condition. PSAT calculates static power flows.
PowerWorld Corporation's PowerWorld Simulatorcalculates static power flows with a visual interface
V&R Energy Systems Research's POM/OPMused for the steady-state contingency analysis and suggesting mitigation measures
Manitoba Hydro International Ltd.'s PSCAD™PSCAD™ is a three phase electromagnetic transient (EMT) simulation program able to analyze power flows in systems that include "electronic power" devices. Electronic power devices, such as those that wind and solar renewable generatioin employ, have extremely fast internal switching transients that traditional power flow programs (e.g. PSS/E) fail to detect.
Electranix Corporation’s E-TRAN / E-TRAN Plus E-TRAN directly translates PSS/E files (.raw, .dyr and .seq) into PSCAD files. E-TRAN Plus for PSCAD allows breaking up and running a large PSCAD case using parallel processing on multiple cores or computers.