The Pacific Direct Current Intertie (PDCI) is a 1354 km, ±500 kV, 3.1 GW, HVDC transmission line from northern Oregon to southern California, consisting of two conductors (bipolar) hung on transmission towers (overhead lines – OHL) without any substations along the way, just two conductor bundles on towers the whole way.

Each end of the PDCI is an HVDC converter station that converts AC to/from DC. The Celilo station of the PDCI is on the Columbia River in Oregon, and the Sylmar station is near Los Angeles in California:

The PDCI is 2-pole (two conductor bundles) with earth (ground) return for single pole use (at half power) if needed (can provide extended emergency use). A ring of ground electrodes provide the northern earth return. Ocean electrodes in the Pacific Ocean provide the southern earth return.

Originally the PDCI transmitted 1.4 GW at ±400 kV. The PDCI will soon be upgraded from 3.1 GW to 3.22 GW, and may later be upgraded to 3.8 GW in the north-to-south direction. Voltage will be upgraded from ±500 kV to ±560 kV.

The PDCI uses both guyed and self supporting towers. Notice in the following photograph the first HVDC tower in the foreground is a guyed tower (referred to as a tangent tower), the second tower is also a tangent tower, and the third tower is self supporting, not guyed, with the overhead lines (OHL) changing direction at the self supporting tower (insulators leaning right indicate line direction changing to the right):

The following photographs show a PDCI tangent tower near Bishop, California:

The PDCI crosses the Oregon / Nevada border at Twelvemile Creek, with self supporting towers because the span is long between the two towers on either side of the creek.