Studies and Reports > 2009 MN Biennial Report > WC Planning Zone > Needs: 6.4.9 Morris 230/115 kV Transformer

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6.4.9 Morris 230/115 kV Transformer

Tracking Number. 2007-WC-N2

Utility. Western Area Power Administration

Inadequacy. Interconnection studies being performed for Big Stone II have identified an overload of the Morris 230/115 kV transformer when the proposed transmission lines are in operation (Big Stone – Johnson Jct. – Morris 230 kV with Big Stone – Canby – Granite Falls built at 345 kV and initially operated at 230 kV). This transformer is owned by Western Area Power Administration.

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Alternatives. To address the overload of the existing 230/115 kV transformer at Morris, it is possible that either a larger transformer be installed to replace the existing 100 MVA unit or a second 230/115 kV transformer be installed in parallel with the existing transformer.

Analysis. This transformer is currently rated at 100 MVA. The pre-contingent (system intact) loading on this transformer has been shown to exceed 100 MVA once Big Stone II is in service. Contingency analysis performed as part of the Big Stone II interconnection study has shown that flows across this transformer can reach up to approximately 170 MVA. Western has completed facilities studies for the Big Stone II project recommending that the existing 100 MVA, 230/115 kV transformer be replaced with a new 336 MVA, 230/115 kV transformer as part of the Big Stone II project (assuming Alternative 1 is implemented). It is not reasonable to install a second 230/115 kV transformer in parallel with the existing transformer at Morris since it would be a much more costly option. A new transformer would be needed and the existing transformer would need to be replaced given that the existing transformer wouldn’t be large enough to accommodate the expected post-contingent flow upon outage of the new transformer.

Schedule. The transformer upgrade will be necessary prior to the in-service date of the Big Stone II project. The Western Area Power Administration is responsible for replacing the transformer through coordination with the Big Stone II project (Tracking Number 2005-WCN1).

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