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High Voltage Direct Current (HVDC)

Page 9:  Pacific DC Intertie (PDCI)

Bipolar OHL

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:

Figure 1: PDCI map.

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.


California

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):

Figure 2: High Voltage transmission lines near Bishop, California: 3,100 MW PDCI (left), and 300 MW HVAC (right). The PDCI (HVDC system on the left in this photograph) carries much more electricity much further, all the way from Northern Oregon to Southern California.

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

Figure 3: PDCI tangent tower near Bishop, California.

Figure 4: Looking up at the tangent tower. Insulators are pointing down (line direction is not changing).

Figure 5: Base of the tangent tower.

Nevada

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.

Figure 6: PDCI crossing Twelvemile Creek. Upper portion of photograph shows the last tower in Oregon. Shadow of the tower indicates it has a wide base (a self supporting tower). Right-of-way (ROW) clearing is not required under the PDCI conductors.

Figure 7: Another section of the PDCI, in Nevada, just south of Twelvemile Creek. A curving dirt road provides access to the towers. Right-of-way (ROW) clearing is not required under the PDCI conductors.

Figure 8: The same section of the PDCI in Nevada, with right-of-way (ROW) of new natural gas pipeline (left) now adjacent to this section of the PDCI. Environmental impact of the pipeline is much greater than environmental impact of the PDCI.

Twelvemile Creek
Figure 9: Topographic (topo) map showing the southern end of the Oregon portion of the PDCI (right side of image), with the last tower in Oregon above Twelvemile Creek. Elevations are in feet (each contour line represents elevation change of 20 feet).

Figure 10: Georeferenced remote sensing image showing the PDCI crossing Twelvemile Creek in 2005. The last tower in Oregon is in the upper portion of image; the first tower in Nevada is lower-right. Right-of-way (ROW) clearing is not required under the PDCI conductors.

Figure 11: Recent topo image showing right-of-way (ROW) of new buried natural gas pipeline. The pipeline (Ruby Pipeline) has much higher environmental impact than the PDCI, requiring all trees and large plants to be permanently removed from its ROW.

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Introduction
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