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Home > Planning > Transmission planning

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 plans

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 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.

2019-2020 Transmission planning process
2018-2019 Transmission planning process
2017-2018 Transmission planning process


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.



  • Draft pro forma approved project sponsor agreement process
    Draft form will apply to project sponsors selected in phase 3 of the transmission planning process, and used to acknowledge acceptance of the sponsor selected; establish the obligations, roles and responsibilities of the sponsor including project milestones; and reflect any binding cost control measures, including binding cost caps that the sponsor agreed to in their application.
  • Previous planning standards
  • Previous transmission economic assessment methodology documentation