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NorthWestern Energy Announces Outage of Generating Station

One of the 50-megawatt units was taken off-line in mid-January due to a vibration alarm. One of the turbines has been removed and sent back to the manufacturer, Pratt & Whitney, for repair. Inspections of the other two units, each of which is fitted with two gas turbines, indicated similar concerns. Although functional at the time, NorthWestern took the remaining units out of service this week to prevent further damage. The turbines, which are under warranty, will be removed and repaired. The plant had a full year of successfully keeping the Montana electric network in balance and operating reliably, as loads on the system and resources available to meet those loads continually move up and down.

"We're concerned about this situation and focused on it. However, we are pleased that the problem was identified promptly and is being addressed. We are working closely with the manufacturer and NAES, the plant's operator, to get the plant back up and running at full capacity as soon as it's safe to do so and to do all of the necessary analysis to prevent this situation from reoccurring in the future," said Bob Rowe, President and CEO.

NorthWestern plans to resume production on each unit as the turbines are inspected, reinstalled, and tested with the first unit back in production perhaps within 45 days. The plant is anticipated to resume full production within 90 - 180 days, barring any unforeseen circumstances.

In the meantime, NorthWestern has entered into contracts with third parties for replacement regulation service and the appropriate filings have been made with the Federal Energy Regulatory Commission (FERC) for these agreements. These agreements will enable the company to provide the necessary services to maintain reliability of its transmission system. The incremental costs associated with the shutdown will be addressed through the normal course of business.

The Dave Gates Generating Station at Mill Creek is located east of Anaconda, Mont., and provides regulating reserve service to maintain transmission reliability within NorthWestern Energy's control area. It was placed into commercial operation on January 1, 2011, and consists of three 50-megawatt natural gas fired units--two of which act as primary units and the third serves as an operational spare.

About NorthWestern Energy
NorthWestern Energy provides electricity and natural gas in the Upper Midwest and Northwest, serving approximately 665,000 customers in Montana, South Dakota and Nebraska. More information on NorthWestern Energy is available on the Company's Web site at www.northwesternenergy.com.

SOURCE NorthWestern Corporation