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.
The annual transmission plan serves as the formal and Board-approved roadmap for infrastructure requirements for the ISO balancing authority.
2021-2022 transmission plan
Plans under development
Process and requirements
Transmission planning standardsThe 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.
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
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
Renewables integration reports and studies
Once through cooling and assembly bill 1318 studiesThe 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 transmission planning standards