Path 66
| Company type | Transmission corridor |
|---|---|
| Industry | Electric power transmission |
| Founded | 1960s (two lines), 1993 (third line) |
Area served | Oregon, California |
Key people | Transmission Agency of Northern California (TANC), Western Area Power Administration (WAPA), Pacific Gas and Electric (PG&E), PacifiCorp |
| Products | Electric power transmission |
California Oregon Intertie (COI), designated as Path 66 by the Western Electricity Coordinating Council (WECC), consists of three parallel 500 kV alternating current transmission lines that connect the electrical networks of Oregon and California. Together, these lines offer a total transfer capability of 4800 MW.
Two of these lines extend from the Malin Substation, located southeast of Klamath Falls, Oregon, to the Round Mountain Substation northeast of Redding, California. One line is owned by the Western Area Power Administration, while the other is jointly owned by Pacific Gas and Electric and PacifiCorp. These two lines, forming part of the Pacific AC Intertie, were constructed during the 1960s. The third line, completed in 1993 as part of the California-Oregon Transmission Project overseen by the Transmission Agency of Northern California (TANC)—a public utilities consortium—runs from Captain Jack Substation near Malin to Olinda Substation south of Redding.
Route
Path 66 incorporates sections of 500 kV lines operated by TANC, PG&E, and PacifiCorp. The TANC line originates at Captain Jack Substation, situated north of Malin and approximately northwest of Malin Substation, where the PacifiCorp and PG&E lines also begin. These substations provide interconnections to both the PacifiCorp and Bonneville Power Administration (BPA) systems in the Pacific Northwest.
- Path 66 - Captain Jack to Olinda
The northernmost section of TANC’s 500 kV line extends from Captain Jack to Tracy Substation within California’s Central Valley. It travels southeast as a single-circuit line running parallel to two other 500 kV circuits across the Modoc Plateau, then turns westward ascending near Grizzly Peak at approximately . The route continues southward over Stonecoal Valley and crosses the Pit River before veering southwest near Round Mountain, where it intersects with two 230-kV lines. From there, it proceeds into the Sacramento Valley, passing Cottonwood, crossing Interstate 5, and turning southward near Olinda Substation to connect with lines transmitting power from Shasta and Keswick Dams.
- Connecting wires to Path 15 - Olinda to Tracy
Beyond Olinda Substation, TANC’s 500 kV line continues as a single-circuit line mounted on two-level towers, running south along the western boundary of the Sacramento Valley roughly parallel to Interstate 5 and several 230-kV lines operated by PG&E and WAPA. A series capacitor station located near Maxwell enhances transmission capacity along this stretch. The line crosses PG&E’s separate 500 kV circuits near Woodland and Rio Vista before paralleling them close to Antioch. All three circuits traverse the Sacramento and San Joaquin Rivers on large pylons before TANC’s line diverges toward Tracy Substation.
- Connecting wires to Path 15 - Tracy to PG&E intersection
At Tracy Substation, this line transitions into a double-circuit 500 kV configuration supported by three-level towers within the San Joaquin Valley. It terminates at an intersection with one of two PG&E 500 kV lines extending south from Tesla Substation toward Los Banos Substation. This setup links Tracy with Tesla Substation and continues toward Los Banos through recently installed towers that have replaced older infrastructure.
- Path 66 - Malin to Round Mountain
The remaining two 500 kV circuits commence at Malin Substation southeast of Captain Jack. A tall BPA dual-circuit line connects Captain Jack with Malin Substation. The PG&E and PacifiCorp lines proceed southward together across the Modoc Plateau alongside WAPA’s line, climbing to an elevation near 5,400 feet (1,645 m) before descending toward Round Mountain Substation, which serves as this segment’s endpoint on Path 66.
Substations
- Path 66
TANC transmission corridor (northbound to southbound)
- Captain Jack
- Olinda
PG&E and PacifiCorp facilities
- Malin
- Round Mountain
- Interconnecting power lines
- Series capacitor station located in Colusa County
- Tracy
Issues
- Transmission capacity
Path 66 is capable of carrying a maximum of 4,800 MW of electricity flowing from north to south, whereas its capacity decreases to 3,675 MW when transmitting from south to north.
- Environmental considerations
The northern transmission route, which includes Path 15, is observable from orbit due to the cleared corridors through dense coniferous forests. These areas undergo logging or clear-cutting to minimize wildfire risks caused by electrical arcing between vegetation and power lines.
Tower design and variations
The TANC 500 kV line utilizes triple-bundled conductors—three wires per phase—differing from PG&E’s double-bundled conductor configuration. Its tower structures contrast markedly with PG&E’s lighter and broader towers and also vary along the WAPA 500 kV route.
At the Olinda substation, the TANC line transitions from delta-style towers near Interstate 5 to two-level tower designs, reflecting enhancements over a pre-existing double-circuit 230 kV line. Southward of the Sacramento River crossing, delta towers that resemble but are distinct from those on the Captain Jack-Olinda stretch are implemented. This segment required establishing a new alignment east of PG&E’s 500 kV lines to comply with separation regulations, visible from Highway 4 and the western Sacramento River Delta region. A portion of the original 230 kV infrastructure remains operational as a 69 kV system serving Contra Costa Canal pumping facilities.
PG&E’s Round Mountain-Malin 500 kV corridor employs towers identical to those found on its Table Mountain-Round Mountain segment. PacifiCorp’s adjacent 500 kV line uses pylons similar in design to WAPA’s Olinda-Captain Jack structures.
- Visual reference
Problems
The Captain Jack-Olinda 500 kV segment of TANC ascends close to near Grizzly Peak, where winter snowfall can accumulate up to at the summit. The substantial build-up of snow and ice on insulators and conductors occasionally results in outages caused by wire breakage under severe weather conditions. This high-altitude portion presents ongoing operational difficulties.