Exelon’s (NYSE:EXC) Potomac Electric Power Company (Pepco) on May 10 filed with the Public Service Commission (PSC) of the District of Columbia the formal notice of construction of the Capital Grid Project.
The project is a positive investment in the capital area that would include building new underground transmission lines, upgrading existing Pepco substations, and eventually building a new substation, the company said. Together, that construction would make the entire capital area power system more flexible, reliable, resilient, efficient, as well as more effective in responding to unforeseen events, according to the company.
Before construction can begin, Pepco must receive approval from the PSC. Pepco added that it is submitting the project to the PSC as two notice of construction (NOC) filings. The May 10 filing is the first NOC filing (representing the first phase of the Capital Grid Project), which includes construction of transmission lines from the Takoma substation to the Champlain substation, as well as upgrades to aging infrastructure.
Specifically, Pepco added, the first NOC filing consists of:
- Construction of two 230-kV underground circuits from the Takoma substation to the rebuilt Harvard substation (the preferred route is 3.81 miles), and from the rebuilt Harvard substation to the rebuilt Champlain substation (the preferred route is 1.27 miles)
- Demolition, site preparation, and substation construction for the rebuilt Harvard substation
- Demolition, site preparation, and substation construction for the rebuilt Champlain substation
The proposed date for construction to begin is:
- March 2018 for the underground transmission portion
- June 2019 – Harvard: demolition, site preparation, and construction
- December 2022 – Champlain: demolition, site preparation, and construction
Pepco said that the second NOC filing – which will likely be filed in early 2018 – will include the work from the rebuilt Champlain substation to the Waterfront substation and will primarily address load-driven needs in Mt. Vernon Triangle, as well as its surrounding neighborhoods. The company said that the second NOC filing will consist of:
- Construction of two 230-kV underground circuits from the Champlain substation to a new Mt. Vernon substation (the preferred route is 2.4 miles), and from the new Mt. Vernon substation to the Waterfront substation (the preferred route is 2.9 miles)
- Site preparation and substation construction for the new Mt. Vernon substation
Pepco said that it will file the second NOC separately so that it can continue to assess the impact of distributed energy resources (DERs) on the timing of the construction of the new Mt. Vernon substation.
Further discussing the need for the Capital Grid Project, Pepco said that 1,300 MW of generation that used to provide a “backup” supply, or redundancy, within the Capital area, and specifically in the District, no longer exists. Even with the contribution of customer generation in the District, almost all of the electricity that serves the District is sourced from outside of its borders and must be supplied through four transmission corridors that terminate in the areas that they serve, creating a radial system, Pepco said.
While the radial lines are adequate in their current configuration to provide service to the area under normal circumstances, should any of the transmission corridors suffer an outage, the radial configuration and the lack of backup supply creates the risk of extended outages to large portions of the District, Pepco said.
The first phase of the Capital Grid Project provides relief to aging substations and begins to develop a networked supply to District of Columbia substations that would increase the resiliency and redundancy of supplies into the city and offset the loss of generation capacity at the retired Benning, Buzzard Point, and Potomac River power plants, Pepco said.
In addition to mitigating the risk associated with the age and condition of the existing facilities, another benefit of the proposed substation upgrades would be the ability to incorporate more DERs onto the electric system, the company said.
The Harvard substation was initially built in 1907, and has undergone several refurbishments through the mid-1960s, Pepco said, adding that the Champlain substation was initially built in the 1930s, with the last incarnation of substation put into service in the mid-1950s.
The proposed rebuilt Harvard substation – which has a proposed in-service date of 2022 – would upgrade the aged equipment in that substation with a high capacity, permanent 230-kV/13-kV substation. The rebuilt Harvard substation initially would serve customers with 140 MVA of firm capacity, Pepco added, noting that the capacity ultimately would be increased to 210 MVA.
The proposed rebuild Champlain substation – which has a proposed in-service date of 2026 – would be built after the load of the existing Champlain substation has been transferred to the rebuilt Harvard substation, Pepco said. The rebuilt Champlain substation would be a high capacity, permanent 230-kV/69-kV/34-kV substation with 572 MVA of firm capacity that would allow for the re-supply of the “L” Street substation 21 with new 34-kV feeders. The rebuilt Champlain substation would also serve as a future source to re-supply 69-kV supplies from the “F” Street and Georgetown substations, Pepco added.
The 230-kV underground transmission lines proposed under the March 10 NOC filing are necessary to provide supply to the rebuilt Harvard and Champlain substations, Pepco said, noting that the two 230-kV underground circuits would be extended a total of about five miles between the Takoma substation 27 in Maryland and the rebuilt Champlain substation.
Construction on the underground transmission portion of the project would extend from March 2018 to June 2022, Pepco said.
The Harvard and Champlain substations are proposed to be gas insulated switchgear (GIS) above-ground indoor facilities, Pepco said. The Harvard substation would be an indoor ultimate 210 MVA GIS facility operating with 230-kV supply feeders, while the Champlain substation would be an indoor 572 MVA GIS facility operating with 230-kV supply feeders. The underground transmission portion involves two 230-kV AC underground transmission lines using cross-linked polyethylene cables installed in concrete duct banks, Pepco added.
Among other things, the company said that the total cost of building the rebuilt Harvard substation is estimated to be about $179m, while the total cost of building the rebuilt Champlain substation is estimated to be about $122m. Pepco also said that the total cost of building the underground transmission is estimated to be about $113m.