Granby Pumping Plant-Windy Gap Transmission Line Rebuild Project

Project Description

Western Area Power Administration owns and operates a 12-mile, 69,000 (69-kV) electric transmission line in Grand County, Colorado, that originates at Windy Gap Substation, located immediately northwest of the intersection of Highway 40 and Highway 125. The single circuit, wood pole, H-frame transmission line generally runs northeast along State Highway 34 and terminates at the Granby Pumping Plant Switchyard at the end of County Road 64.

The proposed project involves rebuilding this single circuit line as a double circuit transmission line and adding a second power transformer. One circuit will replace the existing 69-kV line; the other circuit will be a new 138-kV line. The Granby Pumping Plant Switchyard will be expanded to accommodate the second line and power transformer. Windy Gap Substation will be modified to accommodate the second line. This will be a joint participation project between Western, Tri-State Generation and Transmission (Tri-State), Mountain Parks Electric (MPEI) and the Northern Colorado Water Conservancy District (NCWCD).

Western owns the existing 69-kV transmission line and serves NCWCD loads at Granby Substation, Granby Pumping Plant Switchyard and Willow Creek Pumping Plant. Western also serves MPEI loads at Granby Substation. Tri-State owns the Windy Gap Substation and serves MPEI. MPEI provides the electrical power for Grand County. NCWCD operates the Farr and Willow Creek Pumping Plants.

Purpose

The purpose of this project is to:

• Provide a second source of power to the area between Grand Lake and Granby before failure of the 69-kV cable located in Alva B. Adams water tunnel (also known as the Adams Tunnel Cable)
• Continue to provide reliable, looped transmission supply to MPEI customers in advance of an Adams Tunnel Cable failure
• Ensure the electric system in the area will continue to operate within acceptable voltage criteria while accommodating future load growth in the area and the operation of the Farr and Willow Creek Pumping Plants
• Allow Tri-State to serve its local member (MPEI) with reliable power
• Allow Western to serve its customers in the area in a reliable manner
• Replace a 60-year old overhead transmission line and add shield wires for improved lightning protection

Need

The Alva B. Adams Tunnel is a water diversion tunnel that stretches under the Continental Divide between Estes Park and the Town of Grand Lake. It also contains a 69-kV transmission line in the form of an electric cable owned by Bureau of Reclamation and operated by Western. This cable currently provides a second source of electrical power to the area from Grand Lake to Granby by allowing looped transmission service between Estes Park and Windy Gap Substations. The Adams Tunnel cable has exceeded its predicted useful life and, upon failure, will not be replaced. The Granby Pumping Plant-Windy Gap Transmission Line Rebuild Project is being proposed to address the electrical deficiencies created when the cable fails.

The failure of the cable system will suddenly leave large parts of the MPEI system with only a one-way or radial transmission supply. The part of the MPEI system affected by this transmission system includes members in the area extending from the west side of Rocky Mountain National Park on the north, to the YMCA Snow Mountain Ranch on the south, and from Byers Canyon on the west to the Arapaho National Recreation Area/Continental Divide on the east. Included in this area are the Towns of Hot Sulphur Springs, Granby and Grand Lake, as well as hundreds of customers in the rural parts of that area, particularly along the Highway 34 corridor. Without completion of this project, these customers of MPEI would risk extended power outages especially during adverse winter weather due to the lack of an alternate transmission circuit to supply the area.

The project will insure the electric system in the area will continue to operate within established electrical criteria during motor starting operations at Farr Pumping Plant and Willow Creek Pumping Plant. Engineering studies indicate that once the Adams Tunnel Cable is out of service, the voltage drop when starting motors at Willow Creek Pumping Plant will exceed acceptable limits by the year 2010, if load growth in the area continues at the current rate. This impact would affect both NCWCD and MPEI customers being served by these facilities.