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Studies and Reports > 2009 MN Biennial Report > SE Planning Zone > Needs: 6.7.3 City of Mankato

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Transmission Projects Report 2009
Section 6.7: Southeast Zone
p. 256

6.7.3 City of Mankato

Tracking Number. 2003-SE-N3

Utility. Xcel Energy

Inadequacy. The City of Mankato is supplied by the Wilmarth 345/115/69 kV substation on the north side of the city and a 69 kV transmission line loop around the city. This matter was first reported in the 2005 Report as a two-pronged problem. This year a third concern has been identified. The three separate transmission issues that have been identified are: (1) outage of the Wilmarth-Eastwood-Pohl Road tap results in an overload of the Rutland-Truman 69 kV line and low voltages in the area between Madelia and Decoria, (2) the loss of any of the three 115/69 transformers at the Wilmarth substation results in the overloading of the remaining two and (3) less than desirable reliability due to the large number of common-breaker circuit miles on the existing 69 kV system.

A map of the area is shown following the discussion.

Alternatives. There are two alternatives in the Mankato area to address all the low voltage and thermal overload issues that exist.

Alternative 1: This alternative calls for a new high voltage loop around the City of Mankato by upgrading the existing 69 kV lines to 115 kV. This 115 kV loop can be achieved by implementing the following projects:

  • New 161/115/69 kV substation at South Bend township.
  • Operate existing 161 kV line from South Bend – Wilmarth at 115 kV.
  • Re-terminate the existing 69 kV line from Century – Ballard Corner into South Bend.
  • Build a new 115/69 kV substation at Hungry Hollow
  • Convert the existing 69 kV line from South Bend – Ballard Corner to 115 kV.
  • 115 and 69 kV double circuit from Ballard Corner to Hungry Hollow.
  • Convert the existing 69 kV line from Hungry Hollow – Pohl tap to 115 kV.
  • Convert Pohl substation to 115 kV.
  • Operate the existing 69 kV line, constructed at 161 kV, from Pohl – Eastwood at 115 kV.

The operating voltage of the line between Wilmarth and South Bend has to be lowered from 161 to 115 kV, and the line between Pohl and Eastwood is built to 161 kV specifications and needs to be operated at 115 kV. This option also allows addition of new load on the 115 kV loop without replacement of the Wilmarth 115/69 kV transformers.

Alternative 2: This alternative comprises a new 115/69 kV substation at Hungry Hollow and a new 115 kV line from Eastwood to Hungry Hollow. This alternative will also involve upgrading all three Wilmarth 115/69 kV transformers to higher capacity.

Analysis. Alternative 1 is the recommended plan, as it provides adequate transmission for the current and future needs of City of Mankato. Xcel Energy and Great River Energy jointly applied to the Public Utilities Commission for a route permit for an eight mile long 115 kV line between South Bend and Stoney Creek in August 2008.

Schedule. On April 21, 2009, the Public Utilities Commission issued a route permit for the 115 kV line between South Bend and Stoney Creek. The project is expected to be completed by March 2010.

PUC Docket Number. TR-08-734 (Route Permit)


Transmission Projects Report 2009
Section 6.7: Southeast Zone
p. 258

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