ColumbiaGrid’s 2013 system assessment, which studied the portions of the transmission system operated by participant utilities as well as adjacent transmission operated by other major transmission owners, identified 12 areas of concern that will require attention within the next planning cycle, showed that five areas of concern identified in the 2012 assessment have been resolved and identified no new concerns.
For the 92-page system assessment released July 1, study teams examined five-year and ten-year base cases for winter peak load, summer peak load and light load conditions, taking into account load, generation, external path flows and planned transmission additions that utilities have made a firm commitment to build within the 10-year planning horizon covered by the organization’s biennial transmission expansion plan. Each case was analyzed under pre-outage and outage conditions, any deficient areas that were identified were noted, and corrections or updates were made as appropriate.
The twelve problem areas identified in the assessment included several 230-kV bus outages in the area of Olympia and Shelton, Wash. When the 230-kV bus outages were modeled during the winter cases, no solutions emerged, and load shedding was identified as a possible mitigation measure.
Another problem area identified was in the Orofino area in northern Idaho. In five-year and ten-year summer cases, an outage of the Dworshak-Hatwai 500-kV line or the Hatwai 500/230-kV transformer overloaded the Ahsahka-Orofino 115-kV line and the Dworshak 115/13.8-kV transformer. However, Avista and the Bonneville Power Administration (BPA) have operating procedures and remedial action schemes (RAS) in place to sectionalize the system and redispatch generation for those outages.
In the area of McNary, Ore., a simultaneous outage of the McNary #2 and #3 230-kV buses overloaded the Badger-Nine Canyon Wind-H2F-Berrian 115-kV lines, while an outage of McNary 230-kV bus section #3 overloaded the Cold Springs 230/69-kV transformer. Redispatch of generation at McNary could relieve those problems.
In the Okanogan area of Washington state, a breaker failure at the Wells 230-kV bus would overload the Okanogan-Ophir Tap 115-kV line in the five-year and ten-year winter cases. Douglas County PUD and Okanogan own those facilities. Since there is only one ColumbiaGrid member involved, those issues will be the responsibility of affected parties and no study team was proposed.
In the Pearl-Sherwood areas of Portland, Ore., during the summer case, the N-2 outage of the double circuit Carlton-Sherwood 230-kV and Newberg-Sherwood 115-kV lines overloaded the Sherwood-Springbrook 115-kV line for both the five-year and ten-year cases. The same outage overloaded the Forest Grove-McMinnville 115-kV line in the summer and winter five-year and ten-year cases. BPA and Portland General Electric (NYSE:POR) are working on a solution to this issue.
In the area of Bend, Ore., in the ten-year winter case, bus outages at Pilot Butte 230-kV overloaded the Pilot Butte 230/69-kV transformers. In the ten-year summer case, breaker failures at Redmond West 230-kV bus overloaded the Cove 230/69-kV transformers. Breaker failures at Pilot Butte 230-kV and Redmond 230-kV buses did not solve what may be a symptom of voltage instability. PacifiCorp and BPA own those facilities and those problems were identified in previous system assessments. The unsolved outages could cause voltage stability issues in the Bend-Redmond area.
In the Yakima-Wanapum, Wash., area in the summer, breaker failures and bus outages at Wanapum 230-kV caused overloads on the Outlook-Punkin Center, Moxee-Hopland, Union Gap-Voelker and Ringold-Mesa 115-kV lines, as well as the Outlook 230/115-kV transformer. An outage of the Midway-Wine Country 230-kV line overloaded the Outlook 230/115-kV transformer and the Outlook-Sunnyside 115-kV line.
In the winter, a Wanapum 230-kV bus outage overloaded the Outlook-Punkin Center 115-kV line. While those issues were identified in previous system assessments, overloads on U.S. Department of Energy (DOE) and Avista lines that were previously identified have been resolved. BPA and PacifiCorp own the remaining overloaded facilities, with outage ownership by Grant County. PacifiCorp has identified a project to build a Vantage-Pomona 230-kV line to mitigate this problem but the company has not made a firm commitment to this project, according to the system assessment.
In the area of Troutdale, Ore., in the summer ten-year case, a breaker failure outage of the Troutdale west 230-kV bus overloaded the Troutdale-Linneman 230-kV line, Lacamas-Sifton 115-kV and the St John-Bloss 115-kV line. Loss of the N-2 Ross-Rivergate and Ross-St John lines overloaded the Fruit Valley-Hayden-St John 115-kV line.
In the ten-year winter case, a Ross 230-kV bus section breaker outage overloaded the Troutdale 230/115-kV transformer. Those system issues involve BPA, PacifiCorp and Clark County, Ore., facilities. Since there is only one ColumbiaGrid member, those issues will be the responsibility of the affected parties and no study team was proposed.
Near Centralia, Wash., the N-1 Paul-Satsop 500-kV line outage, the N-2 Paul-Olympia 500kV/ Paul-Satsop 500-kV, and Satsop breaker failures did not resolve in the ten-year winter case, indicating a possible voltage stability issue. Failed solutions only occurred for the N-2 outage involving the Paul-Satsop and Olympia-Satsop 500-kV line outage in last year’s system assessment, but the failed solution for the N-1 outage is new this year, which may indicate that the problem has gotten worse. Load shedding may be a possible solution for this problem.
In the Salem-Eugene, Ore., area, a breaker failure outage at the Albany 115-kV bus overloaded the Fry-Oromet 115-kV line in the five-year and ten-year summer cases. The same outage also overloaded the Bethel-Parish Gap line in the ten-year summer case. In the winter, there were failed solutions for an N-2 outage of the Marion-Alvey and Marion-Lane 500-kV lines. Those problems were identified in previous system assessments, although the issues are less numerous and less severe than in previous years.
Near Sand Point, Idaho, a Libby 115-kV bus outage caused minor overloads on the Bronx-Sand Point line in the five-year and ten-year spring cases. BPA and Avista own those facilities. Similar issues were identified in previous system assessments for the summer season. Reconductoring the Bronx-Sand Point 115-kV line has eliminated those overloads for the summer, but is not sufficient to correct for the loading levels seen in the spring cases. Generation redispatch at Cabinet Gorge would resolve this remaining overload.
The system assessment also identified issues with the Northern Intertie in Washington state. In the five-year and ten-year summer cases, the N-2 loss of the Custer-Monroe 500-kV #1 and #2 lines overloaded the Sedro-Murray, Sedro-Bellingham and Sedro-Horse Ranch 230-kV lines. Those overloads are likely due to RAS arming levels, according to the assessment. Additional generation tripping would eliminate this issue. In both summer cases, a breaker failure outage at the Bothell 230-kV bus overloaded the Snohomish-Bothell 230-kV #1 line. This latter problem was noted in the 2012 system assessment.
The system assessment is the foundation for the organization’s biennial transmission expansion plan and evaluates whether the planned transmission grid can meet established reliability standards.