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How Little Goose Dam was Brought Back Online After Equipment Failure by Sean Wolfe Hydropower Review, October 15, 2024

After a discontinued motor-operated disconnect switch (MOD) failed,
a multiple agency effort ensued to bring the dam back online.

Multiple federal agencies have cooperated to restore Little Goose Dam in southeast Washington to operation following the failure of a crucial piece of equipment.

On the morning of June 14, operators at the U.S. Army Corps of Engineers, Walla Walla District (USACE) discovered that electrical arcing had severely damaged the motor-operated disconnect switch that connects electricity produced by the dam to the grid.

Arcing occurs when a loose electrical connection between conductors forces the current through air gaps, melting the conductors as a result. On high-voltage lines, the arc can reach temperatures as high as 35,000 degrees Fahrenheit.

The motor-operated disconnect switch (MOD) operates as a 14-foot-long motorized light switch that connects two electrical systems. It allows or prevents the flow of electricity, according to Bill Dull, the Walla Walla District reliability program manager.

"The operational significance of the MOD cannot be overstated," said Dull. "This device connects Little Goose's electric power to the 500-kilovolt transmission line; its failure forced four of the six generating units offline."

Little Goose, which lies on the lower Snake River, has a total generating capacity of 930 megawatts (MW), with each generating unit rated at 155 MW. When a unit goes offline, water that would normally flow through a turbine to produce electricity is released over the dam spillway instead. Bonneville Power Administration (BPA) noted that this was "particularly unfortunate" timing, as the Columbia River Basin is experiencing a below-average water year due to lower snowmelt in the Cascades.

Recognizing the impact of a damaged MOD, USACE maintenance crews responded to assess the extent of the damage and find a workable solution.

Dull contacted Rod Morris, who works in BPA's Customer Service Engineering Department, to request technical assistance and see if BPA had a spare MOD unit in reserve.

"I wasn't sure if we would be successful locating the unit, as it is no longer in production," Morris said.

After confirming that BPA did not have a spare, Morris began reaching out to different power utilities and federal partners to locate the discontinued MOD switch. He discovered that the Western Area Power Administration's Sierra Nevada Region will be replacing three of the same model MODs on their system later this year. After a discussion between the three parties, WAPA agreed to transfer ownership of the units to the USACE. The equipment delivery is expected in November.

In the meantime, BPA sent a repair crew to Little Goose to assist USACE in implementing an interim solution while the MOD replacement search was underway. The joint team worked to install a spare jumper that bypassed the damaged disconnect switch, allowing power to flow from the generating units back onto the transmission system. On June 18 at 9:38 p.m., Little Goose was fully back online.

When temperatures rise in the spring and summer months, the electric output of the federal hydropower system becomes increasingly important to the region. The USACE estimates that during the three-day outage, approximately 7,000 megawatt-hours of power was lost due to the units not producing energy.

During prolonged generation outages, sometimes BPA must purchase power from the energy market to meet its demand. More power purchases can increase power rates for BPA's core customer base, so minimizing the outage duration was a priority for both agencies, BPA said.

"It truly was a pleasure working with Rod and the rest of the BPA crew," said Dull. "The collaboration between USACE, BPA, and WAPA-SNR reflects effective multi-agency cooperation with the goal of solving difficult problems in a time of need."

Related Pages:
Drawbridge at Little Goose Dam Fails, Temporarily Closed to Vehicle Crossings by Sean Wolfe, Lewiston Tribune, 12/16/22
Little Goose Dam Extends Public Dam Crossing Closure to April 22 due to Electrical Maintenanceby USACE, Big Country News, 4/18/22
Little Goose Dam to Close Public Dam Crossing from April 4 - 8 to Perform Maintenance by USACE, Big Country News, 3/21/22
Little Goose Dam Closes Public Dam Crossing due to Inclement Weather by by USACE, Big Country News, 1/4/22
Temporary Closure of Little Goose Dam Scheduled for Maintenance Work by USACE, Big Country News, 7/28/21
U.S. Seeks Transformer for 810-MW Little Goose Hydro Project by Sean Wolfe, Hydroworld, 4/2/15
Little Goose Dam Closed to Water Traffic by Greg Craber, Daily Fly, 9/5/18
Little Goose Dam to Have Intermittent Crossing Closures by Sean Wolfe, Walla Walla Union-Bulletin, 6/4/18
Little Goose Lock Reopening Delayed Until April 11 by Matthew Weaver, Capital Press, 3/30/17