A ColumbiaGrid study group has identified an issue that it expects to become more pronounced as more renewable energy is integrated in the Pacific Northwest.
The organization’s West of Cascades North (WOCN) draft study shows the transmission system west of the Cascade mountains will be increasingly stressed, even to the point of exceeding voltage stability limits, as an increasing amount of the region’s thermal generation is periodically replaced by wind or hydro power generated in other areas.
“As we displace generation north of Portland [Ore.], the lines become overloaded, even for a single-line outage contingency,” ColumbiaGrid senior planning engineer Gordon Comegys told TransmissionHub at the group’s March 15 planning meeting in Portland, Ore.
Because the area’s wind and hydro generation is located farther from the load centers than the region’s thermal generation – in some cases, hundreds of miles away – importing those types of power occasionally places extreme stress on the WOCN interface.
While the WOCN interface comprises a group of 500-kV lines in the area west of the Cascades from the Canadian border to south of Seattle, the broader area adversely affected includes Washington’s Puget Sound region and Oregon’s Willamette Valley.
The stresses created depend on where the increased power originates and which transmission lines and facilities experience increased loads as a result, Comegys said. “The wind energy comes from the south, such as Walla Walla or from along the Columbia River, and stresses the system less than hydropower that comes from the north” because wind generation is more spread out, he said. Hydro sources are in a more concentrated area and therefore have a more pronounced effect on the WOCN interface, Comegys said.
The study, which is currently in draft form, identifies 10 project options which, in varying degrees, would help alleviate system constraints that arise when thermal generation is ramped down to accommodate renewable generation.
The project identified as having the greatest benefit is a recommendation to build a new 120-mi, 500-kV transmission line from the Army Corps of Engineers’ Chief Joseph dam in Bridgeport, Wash., to the town of Monroe in western Washington. Comegys said that specific option showed more benefit than other study options that added a new cross-mountain transmission line.
The study also identified projects with shorter implementation times than building a new line, though the benefits were less robust. Those included reconductoring existing lines, voltage upgrades, and adding series capacitors to existing lines to help alleviate overloading of the WOCN interface.
The study will be presented for approval at the March 27 meeting of ColumbiaGrid’s Cross Cascades Study Team.