Project Description
The Cascade Project will have three main physical components: a 100-mile, underwater and underground power cable bundle extending between The Dalles and Portland; and two electrical converter stations, one at each end of the cable.
The Cascade Project transmission cable consists of a bundle of two power cables – each only about 6 inches in diameter – and a fiber optic communications cable. For the most part, the cable bundle will be installed under the Columbia River over the course of a few months, taking extreme care not to disturb sensitive river habitats or existing river uses. Between the river and the interconnection points at The Dalles and Portland, there will be short stretches of line buried underground. In addition, the cable bundle will exit the river for about 7.5 miles to bypass the Bonneville Dam.
The underwater cable will be installed using established, benign jet plow technology of the type used for numerous underwater installations. As shown on the figure, the cables are fed from a ship or barge into the blade of the jet plow which is towed by the installation vessel. High-pressure water jets fluidize the river bottom sediment, creating a narrow (approximately 18 inches) trench for the cable bundle. As the plow moves forward, the cable bundle settles into the trench at the prescribed depth, where the fluidized sediment settles back over the bundle.
The Project will feature Voltage Sourced Converter-High Voltage Direct Current (VSC-HVDC) technology, characterized by controllability, compact design, and ease of interface with interconnecting systems. A converter station will be built at both ends of the line, adjacent to existing substations, and similar to these substations in overall appearance. The technology for Cascade will be comparable to that used for the Trans Bay Cable Project in San Francisco, which has been reliably operating and meeting approximately 40% of the greater San Francisco area’s power needs since 2010.
Because of its modularity and scalability, a VSC HVDC converter station can be adapted to fit the conditions of its site. The Project converter stations will require approximately 5 acres each, and their final configurations will be determined based on detailed site investigations. Final design of each converter station will be in accordance with approved site plans that take into account local zoning requirements.
