The Colorado Public Utilities Commission, in a July 11 decision, granted Tri-State Generation and Transmission’s May application for a certificate of public convenience and necessity (CPCN) for the construction of the estimated $16.2m Gateway Transmission Project, which consists of a new 230/115/12.47-kV substation.
The commission said that the application is unopposed. The commission noted that it “finds that the proposed project is needed to serve load growth and for reliability purposes.”
As noted in the decision, Tri-State had requested that the commission:
- Grant the CPCN
- Find that the 115-kV transmission facilities to be built in conjunction with the project are in the ordinary course of business and do not require a CPCN or, in the alternative, grant a CPCN for such facilities
- Make specific findings that the expected maximum level of magnetic fields that could be experienced under design conditions at the end of the project’s property boundaries and transmission line rights of way (ROWs), at a location one meter above the ground, are 150 mG or less and are, therefore, reasonable and need not be mitigated to a lower level
- Make specific findings that the projected level of audible noise radiating beyond the project’s property lines and transmission line ROWs at a distance of 25 feet are less than 50 dB(A) and are, therefore, reasonable and need not be mitigated to a lower level
The commission noted that Poudre Valley Rural Electric Association (PVREA), one of Tri-State’s member systems, is experiencing native load growth on its system in northern Weld County, and that in order to serve that growth, Tri-State and PVREA are planning to build the project. The project is needed to facilitate service by Tri-State’s member system to the identified and forecast distribution loads in PVREA’s service territory. The commission added that the project is also expected to increase system reliability for PVREA and Public Service Company of Colorado, as well as for Tri-State’s existing loads.
The substation – which consists of 230-kV and 115-kV circuit breakers configured in such a way to be expandable, as well as a 150 MVA transformer – will be located adjacent to the existing Platte River Power Authority (PRPA) Boyd-Longs Peak 230-kV transmission line, which will run through the Gateway substation, the commission noted.
PRPA will be responsible for sectionalizing its line to serve the Gateway substation and will also build the 230-kV transmission spans that are necessary to connect the substation to the line, the commission said. The planned PRPA 230-kV facilities – which will be designed, built, and owned by PRPA – are not part of Tri-State’s CPCN request, the commission noted.
As part of its project, Tri-State plans to build a short 115-kV transmission line to interconnect with Tri-State’s existing Boyd-Lone Tree 115-kV transmission line. The commission added that while Tri-State considers the 115-kV facilities to be in the ordinary course of business under commission rules, it requests an affirmative ordinary course of business determination by the commission for those facilities.
The project requires no new transmission lines to be built, and the 230-kV to 115-kV interconnection, as well as the Gateway 12.47-kV distribution substation, will be built on a single portion of property and within the same fence line, the commission said.
The magnetic fields from the energized conductors in the substation were modeled using a three-dimensional magnetic field model prepared by Southern California Edison, the commission said, adding that the magnetic fields from the 115-kV transmission tie lines were modeled using the Bonneville Power Administration (BPA) Corona 3 program.
The results of the modeling indicated that the level of magnetic fields at the edge of the ROW from the substation transformers and 115-kV transmission lines will be well below the 150 mG deemed reasonable by commission rules, the commission said.
The audible noise from the substation transformers were predicted using the “Cadna/A” noise model, the commission said, adding that the audible noise from the 115-kV transmission tie lines was predicted using the Corona 3 model from the BPA. The results of the models show that the level of noise 25 feet from the property line and ROW boundary for all operating conditions will be less than 45 dB(A), less than the commission residential limit of 50 dB(A), the commission said.
Among other things, the commission said that the magnetic field values and audible noise values for the project meet the conditions of the commission rules regulating electric utilities, are deemed reasonable, and therefore need not be mitigated to a lower level.