Black Hills Power d/b/a Black Hills Energy on Feb. 5 filed with the South Dakota Public Utilities Commission an application seeking authority to build a new 230-kV/69-kV substation at the location of the former Ben French power plant, along with a new 230-kV transmission line.
The substation portion of the project would be contained within Black Hills’ property formerly containing the Ben French power plant, located on the northwest side of Rapid City, S.D. Black Hills added that new line would be built from the substation southeast about 0.2 miles and then east about 0.5 miles. The line would be built completely within an existing Black Hills easement.
Discussing the purpose of the facility, Black Hills said that its customers in the Rapid City, S.D., area are served by two parallel 230-kV/69-kV transformers at the Lange substation and a single 230-kV/69-kV transformer at the South Rapid City substation. Those transformers feed the Rapid City 69-kV sub-transmission network, the company said, noting that there is 130 MW of nameplate generation capacity installed on the Rapid City 69-kV network.
Evaluating the simultaneous loss of two of the three transformers in Rapid City is considered a Category P6 outage as defined in the TPL-001-4 NERC Reliability Standard. For the loss of the two larger 150 MVA transformers under peak load conditions, overloads on the remaining 100 MVA transformer may be encountered, which is due to insufficient generation capacity and sub-transmission energy import capability, the company added.
Transformer overloads can lead to equipment damage, reduced transformer lifecycle and potential catastrophic failure, Black Hills said, adding that a corrective action plan is needed to address the overload and maintain compliance with the reliability standard. The importance of the upgrade is emphasized since a large transformer may be considered a “long lead time” piece of equipment and temporary operating measures are often not a viable solution for longer periods of time, the company said.
The estimated cost for the project is estimated to be about $9.7m – that is, $8.1m for the substation and $1.6m for the 230-kV transmission line, Black Hills said.
Among other things, Black Hills said that the proposed project would follow existing roads and quarter lines, and should have no adverse long-term impact on the vegetation and wildlife composition within the project area.