Pacific DC Intertie

Pacific DC Intertie. The Pacific DC Intertie is a high-voltage direct current (HVDC) electric power transmission line that extends from the Pacific Northwest to Southern California. It is one of the world's longest and highest-capacity HVDC lines, playing a critical role in the Western Interconnection grid. The system facilitates the efficient bulk transfer of electrical energy, primarily from hydroelectric resources in the north to major load centers in the south.

Overview

The intertie is a bipole system operating at ±500 kilovolts, connecting the Celilo Converter Station near The Dalles, Oregon, to the Sylmar Converter Station in Los Angeles. It is owned and operated jointly by the federal Bonneville Power Administration and the municipal Los Angeles Department of Water and Power. This infrastructure enables the exchange of up to 3,100 megawatts of electricity, which is essential for grid stability, economic power purchases, and integrating diverse generation resources across state lines. The line traverses diverse terrain, including areas managed by the United States Forest Service and the Bureau of Land Management.

History

Planning for the intertie began in the early 1960s, driven by the need to transmit surplus hydroelectric power from projects like the Grand Coulee Dam to growing markets in California. The project was a landmark achievement for the General Electric company, which supplied the pioneering mercury-arc valve converter technology. Construction commenced in 1965, and the line was officially energized in 1970, marking a major milestone in HVDC technology in North America. Its success demonstrated the viability of long-distance direct current transmission and influenced subsequent projects like the Interstate Power and Light network and the Quebec – New England Transmission.

Technical specifications

The system utilizes a bipolar configuration with a nominal voltage of ±500 kV DC and a transmission capacity of 3,100 MW. The original mercury-arc valve converters at both Celilo Converter Station and Sylmar Converter Station were replaced with solid-state thyristor technology in the 1980s and early 2000s, greatly improving reliability and control. The overhead line consists of bundled conductors supported by lattice steel towers designed to withstand the environmental conditions of the Cascade Range and Mojave Desert. Key components include smoothing reactors, DC filters, and extensive SCADA systems for real-time monitoring and management by entities like the Western Area Power Administration.

Operations and significance

Operations are coordinated through the North American Electric Reliability Corporation and California Independent System Operator markets. The intertie allows Southern California Edison and Pacific Gas and Electric Company to import cost-effective power, often from Columbia River hydro systems, to meet peak demand, especially during summer months. It provides crucial voltage support and grid inertia, enhancing reliability for millions of customers from Portland to San Diego. The line's ability to reverse power flow is also strategically important, allowing for emergency power transfers during events like the California electricity crisis or regional shortages.

Upgrades and future developments

Major upgrades include the complete thyristor valve replacement at Sylmar Converter Station following damage in the 1994 Northridge earthquake and ongoing advancements in converter control systems. Studies by the United States Department of Energy and partners like the Electric Power Research Institute explore expanding capacity or adding new parallel circuits to accommodate increasing renewable generation from wind farms in Wyoming and solar power in the Southwest. Potential future developments may involve interconnection with other HVDC projects, such as the proposed TransWest Express transmission line, to further integrate the Western Interconnection and support clean energy goals.

Category:Electric power infrastructure in the United States Category:High-voltage direct current transmission lines Category:Buildings and structures in Oregon Category:Buildings and structures in Los Angeles