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Transmission planning for a reliable, economic and open grid

Transmission planning at the ISO actively engages stakeholder and public input and uses the best engineering analysis possible to determine short- and long-term infrastructure needs.

Transmission plan

The annual transmission plan serves as the formal and Board-approved roadmap for infrastructure requirements for the ISO balancing authority.

Current plan

Plans under development

Process and requirements

  • Transmission planning standards
    The Planning Standards assure consistent reliability standards across the ISO controlled grid, above those established by NERC and WECC, that will maintain or improve transmission system reliability to a level appropriate for the California system and will ensure secure and reliable operation of the ISO controlled grid.
  • ISO CEC and CPUC Memorandum of Understanding
  • ISO, CEC and CPUC planning and procurement process alignment
    Alignment of the transmission planning process with CEC Integrated Energy Policy Report (IEPR) demand forecast and CPUC Long Term Procurement Plan (LTPP) proceeding.
  • Transmission planning documents
    • Request Window Submission Form and Attachment A
      Form used in Phase 2 during the two-month Request Window to submit potential mitigation solutions, either transmission or non-transmission alternatives, to address reliability constraints identified in the current planning cycle.
    • FAC-002-4-R6 Qualified Change Technical Bulletin
      Definition of qualified change in compliance with FAC-002-4 R6 Facility Interconnection Studies.
    • Project sponsor documents
      These are documents used for project sponsors submitting proposals for the Phase 3 competitive solicitation process.
    • Approved project sponsor document
      This document is applicable to Approved Project Sponsors selected in the Phase 3 competitive solicitation process.
    • Planning coordinator services
    • Submittal requirements - data for power system modeling and analysis - MOD-032-1
      Documentation regarding base case development and data submittal requirements for transmission and generation owners in accordance with NERC Reliability Standard MOD-032-1
    • Submittal requirements - data for power system modeling and analysis - Transmission Planning Process (TPP) BPM
      Data templates, resource list, and documentation regarding base case development and data submittal requirements for participating generator owners in accordance with ISO’s transmission planning process BPM

Transmission planning and studies

ISO and participating transmission owner studies demonstrate how the ISO is planning for infrastructure needs while meeting North American Electric Reliability Corporation and ISO planning standards.

  • Previous transmission planning processes
    • 2022-2023 transmission plan
    • 2021-2022 transmission plan
    • 2020-2021 transmission planning process
    • 2019-2020 transmission planning process
    • 2018-2019 transmission planning process
    • 2017-2018 transmission planning process
    • 2016-2017 transmission planning process
    • 2015-2016 transmission planning process
    • 2014-2015 transmission planning process
    • 2013-2014 transmission planning process
    • 2012-2013 transmission planning process
  • Transmission access charge forecast model
    This model is used to project TAC impact of the capital program in each year’s transmission plan.
    • 2022-2023 transmission access charge forecast model
    • 2021-2022 transmission access charge forecast model
    • 2020-2021 transmission access charge forecast model
    • Archive - transmission access charge forecast model

  • Transmission capability information provided to the CPUC
    • Transmission capability estimate inputs for CPUC integrated resource plan - Jul 05, 2023
    • Transmission capability estimate inputs for CPUC integrated resource plan - Jul 27, 2021
    • Transmission capability estimate inputs for CPUC integrated resource plan - May 28, 2019

Accessing transmission data

Transmission planning base case data

The ISO provides access to its regional transmission planning base case data and dynamic data files to members of the Western Electricity Coordinating Council (WECC) and non-WECC members who have an approved WECC Base Case Data Request Package prior to requesting access to this data. Requesting entities must submit a Regional Transmission Non-Disclosure Agreement (NDA). Please review the Submission Instructions before submitting any forms for thorough instructions and links to the necessary forms.

Instructions to access positive sequence load flow data and dynamic models descriptions

General Electric International, Inc. (GEII) is the only party authorized to distribute GE Positive Sequence Load Flow (PSLF) reference manuals to other parties. A non-PSLF licensed user wanting copies of the load flow data and dynamic models export/import documents needs to contact GEII. Please direct all questions and access requests for a PSLF license to GEII at


Previous reports and studies

  • Once through cooling and assembly bill 1318 studies
    The California ISO annual transmission planning process will be the main vehicle for the ISO to evaluate potential reliability impacts arising from implementation of California’s once-through cooling policy and air emission constraints in Southern California. Transmission planning studies will establish the potential reliability impacts of the State Water Resources Control Board policy that restricts the use of coastal and estuarine waters for power plant cooling. Planning studies will also address any system reliability issues associated with the lack of air permits available for new plant construction in the South Coast Air Quality Management District.