Virginia State Corporation Commission staff, in an April 27 report filed with the commission, concluded that Virginia Electric and Power d/b/a Dominion Energy Virginia has reasonably demonstrated the need for the proposed underground Idylwood-Tysons 230-kV single-circuit transmission line.
As staff noted, the company last November filed an application with the commission requesting a certificate of public convenience and necessity (CPCN) for the proposed line. Staff said that it does not oppose the issuance of the requested CPCN.
The company proposes to:
- Build the new single-circuit, 230-kV underground transmission line, designated 230-kV Idylwood-Tysons Line #2175, to run about 4.3 miles from the company’s existing Idylwood substation to the company’s existing Tysons substation
- Rebuild the Tysons substation using gas insulated substation (GIS) equipment to accommodate a six-breaker 230-kV ring bus within the existing property boundaries
- Install new gas insulated line (GIL) terminal equipment at the Idylwood substation for the new Line #2175 installation
- Perform relay work at the Reston substation
Staff added that the project, which is located entirely in Fairfax County, Va., and has an expected in-service date of June 2022, is estimated to cost $121.8m, including:
- About $89.4m for the new 230-kV cross-linked polyethylene (XLPE) underground transmission line
- About $31.5m for conversion of the existing Tysons substation to GIS
- About $790,000 for station work at the existing Idylwood substation
- About $118,000 for relay work at the existing Reston substation
According to the company, the proposed project is necessary to ensure that Dominion Energy Virginia can maintain and improve reliable electric service to its customers within the growing Tysons and McLean area of Fairfax County.
Staff added that according to the company, the project is also needed to address potential NERC violations projected to occur under certain contingency conditions along a section of the company’s transmission system described as the Tysons Loop, which is about 20.8 miles long and consists of four substations – Tysons, Swinks Mill, CIA, and Reddfield – connected by these four 230-kV, single-circuit transmission lines:
- Line #2010 from the Reston substation to the Tysons substation
- Line #2108 from the Tysons substation to the Swinks Mill substation
- Line #2029 from the Swinks Mill substation to the CIA substation
- Line #2035 from the CIA substation to the Idylwood substation
According to the company, staff said, in the contingency event of an N-1-1 loss of Line #2010 between the Reston substation and the Tysons substation, and Line #2035 between the Idylwood substation and the Reddfield substation, there would be a loss of the load associated with the four substations within the Tysons Loop.
Staff added that according to the company, by 2023, the projected loading on the Tysons Loop is expected to reach about 343.4 MW, triggering a NERC violation if that load is lost under the N-1-1 contingency.
The proposed project would split the load on the Tysons Loop such that the Swinks Mill, CIA, and Reddfield substations would be sourced from the loop that starts at the Tysons substation and ends at the Idylwood substation – the Swinks Mill Loop – and the future Spring Hill substation would be sourced from the loop that begins at the Reston substation and ends at the Tysons substation – the Spring Hill Loop. As a result, staff added, under the aforementioned N-1-1 event, the total load lost within the Tysons Loop would be reduced below the 300 MW threshold, avoiding a NERC violation. The proposed project would also network the Tysons substation with three transmission lines, thus yielding a more robust substation, staff said.
The company states that the 4.3-mile proposed route would be built within the company’s existing transmission right of way (ROW) or within road ROW belonging to the Virginia Department of Transportation (VDOT) or Fairfax County. Staff added that the company also said that the project would be built using open trenching and horizontal directional drilling (HDD) technology. The line would be built in new 30-foot-wide ROW permanent easements, transportation ROWs of varying width obtained through permit, and on the company’s existing ROW.
At 0.2 mile, the proposed route and “Underground Alternative 04” would cross the least amount of private land, staff added. Also, the proposed route and “Underground Alternative 06” would not require the clearing of any forested land outside of the existing ROW, staff noted. In addition, while still disruptive during construction, the use of underground construction would minimize the visual impact on the existing multi-family and single-family residences in the area, staff said.
Among other things, staff said that it agrees with the company that the proposed route – which is the least expensive route compared to all of the other routes –provides the most optimal route for the proposed project.