The Public Service Commission of Wisconsin, in a recently issued final decision, granted, subject to conditions, the application of the city of Plymouth for authority to replace the existing 69/12.47-kV, 15/20/25 megavolt ampere (MVA) transformer at its Substation No. 2, which is located within the city, near the intersection of County Trunk Highway PP and Short Cut Road.
As noted in the decision, Plymouth – a municipally owned electric public utility – proposed to replace the existing transformer that is currently connected to American Transmission Company’s (ATC) 69-kV system with a new 138/12.47-kV, 20/33 MVA transformer connected to ATC’s existing 138-kV system. Plymouth further proposed to add a second 138/12.47-kV, 15/25 MVA transformer at its Substation No. 4, located near the intersection of County Road M and County Road JM, in the town of Sheboygan Falls, Sheboygan County.
The decision added that the estimated total cost of the proposed project is about $4.8m, based on an in-service date of 2019, with ATC’s portion of the project estimated at $2.1m; commission authorization is not required for ATC’s portion of the project.
According to the decision, the need for the proposed project is driven by system upgrades and the need for increased reliability of the system, which means it is unlikely that renewable resources or other forms of generation would be a cost-effective alternative. The decision also said that:
- No significant environmental consequences are associated with the project
- While alternatives to the proposed project have been considered, no other reasonable alternatives to the project exist that could provide adequate service in a more reliable, timely, cost-effective, and environmentally responsible manner
- Energy conservation, renewable resources, or certain energy priorities, or their combinations, are not cost-effective, technically feasible, or environmentally sound alternatives to the proposed project
- The general public interest and public convenience and necessity require completion of the proposed project
The decision noted that Plymouth purchases all of its energy requirements from WPPI Energy through ATC-owned 69-kV and 138-kV transmission facilities at Plymouth’s four substations, including Substation No. 2, which has a peak load of 23.44 MVA and is served by a radial 69-kV line from the North Mullet River substation, and Substation No. 4, which has a peak load of 12.34 MVA and is served by a 138-kV line from the Mullet River substation.
Further describing the project, the decision noted that a single 22-year-old transformer is installed in Substation No. 2 and operates at 94% of its extended rating of 25 MVA. Diagnostic testing and inspection indicates that internal arcing/gassing will become a major problem in the near future, according to the decision. Plymouth proposes to decrease the loading on the substation and replace the existing transformer prior to failure, the decision said, adding that the existing transformer in Substation No. 2 will be moved and stored as a spare for emergency use in Substation No. 3, which has a peak load of 11.38 MVA and is served by a radial tap off 69-kV line that is referred to as the Y50 line.
The decision noted that Plymouth proposes to retire the existing 69-kV line and establish a new 138-kV interconnection with ATC; the proposed 138-kV interconnection and associated 500 feet of 138-kV transmission line will be built by ATC.
Discussing the Substation No. 4 component of the project, the decision said that the commission in September 2006 authorized the city to build and place in service that new substation, at the estimated total cost of about $1.5m. That substation, with a single transformer, has been in service since late 2007; has a peak load of 12.34 MVA; and is also served by the 138-kV line from the Mullet River substation.
In design and construction of Substation No. 4, accommodation for a second transformer was taken into consideration, the decision added, noting that transmission level switching will be achieved by adding 138-kV breakers in that substation. The addition of a second transformer and associated 138-kV breakers will address the need for backup transformer capacity, the decision said.
Among other things, the decision said that if Plymouth does not begin on-site physical construction within one year of the effective date of the final decision, the certificate authorizing the approved project is to become void unless Plymouth files a written request for an extension of time with the commission before the date on which the certificate becomes void, and is granted an extension by the commission.