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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.

Current transmission plan (2013-2014 planning cycle)
The annual transmission plan serves as the formal and Board-approved roadmap for infrastructure requirements for the ISO balancing authority.


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.

2015-2016 Transmission planning process
2014-2015 Transmission planning process
2013-2014 Transmission planning process
2012-2013 Transmission planning process
2012-2013 Transmission planning process - additional study assessments

Western planning region coordination

The ISO and regional entities throughout the western interconnection collaborate during their transmission planning processes to ensure regional transmission stability and efficiency.

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 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 General Electric and sign a non-disclosure agreement. Please direct all questions and access requests for a PSLF license to GEII at http://www.gepower.com/prod_serv/products/utility_software/en/ge_pslf/index.htm.


Previous reports, studies and planning standards

  • 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.

 Previous planning standards


  • 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.