Strategic Transmission Expansion Plan


IID has proposed a multiregional strategic transmission expansion alternative to the California Independent System Operator and WestConnect that, as proposed, would expand the export of renewable energy to the state and the Southwest region while ensuring that the district maintains its balancing authority, meets federal and state regulations and replaces generation lost by the retirement of the San Onofre Nuclear Generating Station.

Initial Phase
The plan proposes the construction of a 2,200 megawatt 230 kV collector system in the IID service territory. IID proposes to finance, construct and upgrade its internal transmission network, creating an internal collector system that would facilitate the export of 1,100 megawatts to the CAISO and simultaneously another 1,100 megawatts to the WestConnect.

Construction would include: 

  •  a double circuit 230 kV collector system, connecting six substations, creating a robust internal 230 kV network
  • creation of two new substations
  • development of a single 500 kV line, AC rated at 1,200 megawatts, to connect Arizona Public Service’s North Gila substation to IID’s Highline substation
  • construction of a 1,100 megawatt 500 kV DC transmission line from the Salton Sea area to the San Onofre Nuclear Generating Station substation

As the need for additional renewable energy generation occurs, IID would be able to add a 500 kV collector system to the 230 kV system, upgrade the Path 42 line from 230 kV to 500 kV and add a second circuit on the DC line towers. These future upgrades would increase export from 2,200 megawatts under STEP Phase 1 to 4,100 megawatts.

STEP Factsheet 2-20-2014 [PDF] 

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