Studies and Reports > 2009 MN Biennial Report > SE Planning Zone > Needs: 6.7.13 Cannon Falls Area

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6.7.13 Cannon Falls Area

Tracking Number. 2009-SE-N3

Utility. Xcel Energy

Inadequacy. There are two 115/69 kV transformers at the Cannon Falls Substation and loss of either one will overload the remaining transformer. In addition, should a circuit breaker at Colvill Substation fail to operate, the resulting switching will cause overloads.

A map of the area is shown following the discussion.

Alternatives. Several alternatives were studied to help resolve this outage situation.

Option 1 Spring Creek to Cannon Falls 69 kV line rebuild to 115 kV. This option would rebuild the existing Cannon Falls to Spring Creek 69 kV line to 115 kV, convert all of the substations along the route, and add a new substation to feed the 69 kV system. A variation of this option would have the line end at Colvill instead of Cannon Falls.

Option 2 New Miesville Tap 161/69 kV Substation. This option would create a new 161/69 kV substation designed to allow for a fault on the 161/69kV transformer to not cause the 69 kV lines to be lost. Some substation work at Colvill Substation would occur and a ring bus would be added to Cannon Falls Substation. This option effectively unloads the Cannon Falls 115/69 kV transformers by providing another source to the 69 kV system.

Option 3 New 115 kV line from West Faribault to Cannon Falls. This option would create a new 115 kV line from West Faribault to Cannon Falls. The new line would run roughly parallel with the existing 69 kV line that runs from West Faribault to Cannon Falls.

Option 4 New 115/69 kV Transformer and Breaker Change at Colvill Substation. This option involves changing the existing breaker configuration at Colvill Substation and adding a ring bus at Cannon Falls Substation. At Colvill Substation a new 115/69 kV transformer would be installed and a new 69 kV line would be built two miles to the existing Cannon Falls to Byllesby 69 kV line. The transmission lines around Colvill Substation would also be reconfigured. Some equipment upgrades at Byllesby Substation would be necessary to increase the capacity on the 69 kV system under contingency. This option unloads the Cannon Falls transformers by providing another source to the 69 kV system.

Option 5 New Transformer and Breaker Sectionalizing at Colvill Substation At Colvill Substation a new 115/69kV transformer would be installed and a breaker row would be added. A new 69kV line would be built 2 miles to the existing Cannon Falls to Byllesby 69kV line. Breaker failure sectionalizing will be added to three breakers. This option minimizes the work done at Colvill substation while still unloading the Cannon Falls transformers by providing another source to the 69 kV system.

Option 6 Distributed Generation.

Analysis. This inadequacy was uncovered during Xcel Energy’s 2008 NERC compliance assessment. A more detailed study looking at the above six options was conducted to determine the preferred alternative.

Options 2, 4, and 5 were the most attractive options. In the end, Option 5 was selected as the alternative to pursue because no work is needed at the Cannon Falls Substation as part of this alternative and because the costs, estimated at $5,500,000, are the lowest of the options. In addition, this option can be most easily implemented from a construction standpoint.

Option 1 was not considered after an initial analysis determined it would cost approximately $30,000,000. This cost is too high for the low load area it would cover and other options are as effective and cost less.

Option 3 was rejected after an initial analysis determined that the project would cost approximately $17,000,000. This cost is too high and other options are more effective and cost less.

Option 6 (distributed generation) is not believed to be a viable alternative to address these inadequacies. With the installation of the new 350 MW generator in the area, there is adequate generation to serve load in the area. The critical contingencies reduce the capacity of the system for that generation to access the transmission grid.

Schedule. The recommended alternative is expected to be in service by summer 2010.

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