California's electric grid operator is examining how to boost carrying capacities on major transmission lines to bring more electricity from the Pacific Northwest to displace gas-fired generation tied to the Aliso Canyon natural gas storage facility in Los Angeles County.

The California ISO relies heavily on gas-fired generation to maintain reliable electric service in the region, and those generators require fuel from Aliso Canyon. However, Gov. Jerry Brown asked the California Energy Commission to plan for permanent closure of Aliso Canyon after he declared a state of emergency when Sempra Energy subsidiary Southern California Gas Co.'s facility developed a major leak that created a fuel supply shortage.

Early this year Energy Commission Chair Robert Weisenmiller and California Public Utilities Commission President Michael Picker urged the ISO to help by studying ways to increase transmission capacity to bring more hydroelectric power from the Pacific Northwest to Southern California.

The objective of the study is to determine the existing transfer limits on major long-distance transmission lines, known as interties, and develop alternatives to increase their capacity.

On Nov. 26 the ISO presented to stakeholders a report outlining progress on a study of options to increase the power carrying capabilities of the California-Oregon Intertie and Pacific Direct Current Intertie, which both connect Oregon and California. The goal is to produce a final draft transmission plan by Jan. 31, 2019, but future studies will be required.

The California-Oregon Intertie, also known as Path 66, is a combination of three jointly owned 500-kV alternating-current lines connecting California and Oregon with a combined southbound rated capacity of 4,800 MW and 3,675 MW northbound. The Pacific Direct Current Intertie, with a capacity of 3,100 MW northbound and 3,220 MW southbound, is an 846-mile north-south transmission link from the Celilo Converter Station near the Dalles Dam on the Columbia River to the Sylmar Converter Station near Los Angeles.

The aim of assessing whether capacities can be increased on these interties requires a complex evaluation of many variables and alternatives for coordinating operations between the Northwest and California. For example, fluctuations in hydropower production have an impact on the availability of transmission capacity.

Load forecast assumptions, variable renewable generation, transmission scheduling and market needs must be factored into the studies. Remedial action schemes to automatically trip generators to relieve transmission problems and many other operational issues are under review.

Cooperation with multiple transmission owners and other parties, such as the Bonneville Power Administration and the Northwest Power and Conservation Council, is required. The California Oregon Intertie, for example, has multiple owners and parties with scheduling rights in California and Oregon.

The ISO is not talking about a quick fix, but is addressing issues in terms of a "near-term" assessment for 2023 and a longer-term assessment for 2028.

In addition to transmission improvements, increased battery storage, energy efficiency and demand response are being examined for the eventual replacement of Aliso Canyon.

"Clearly, increasing the transfer of low-carbon supplies to and from the Northwest can be one of the multiple puzzle pieces that we must examine to build a cumulative phase out strategy," Weisenmiller wrote in the letter to the ISO, which Picker co-signed.