Idaho Falls Power is hanging by the proverbial thread—a single transmission line through a single substation connects thousands of homes and businesses in and around the city to the regional grid. If the Goshen substation goes down, power is out for miles around.
"That really scares me," Idaho Falls Power system engineer Ben Jenkins said.
An outage on Dec. 4, 2013, left thousands without power for hours in subzero weather. Since then, Idaho Falls Power has worked with Idaho National Laboratory to figure out if the municipal utility's small hydropower plants could be used as "black start" resources—resources that can restore electricity to a grid without relying on the external transmission network—or at least to power a microgrid if the transmission system fails. The utility owns five low-head, run-of-the-river dams with a combined capacity of about 50 MW.
In 2017, the utility and lab decoupled an 8 MW dam from the grid and tried to use it as a black start resource as if the region had gone dark. As they increased generation, the water column started oscillating.
"When we hit about 3 MW, the generator went completely unstable," Jenkins said.
The vibration, or mechanical resonance, threatened to tear apart the machinery. A similar test in the early 1980s hit the same wall. Oscillation ripped apart the first Tacoma Narrows Bridge, dubbed Galloping Gertie, in 1940, he noted.
Jenkins and Thomas Mosier at INL were sure that if the generators could push past the wall, the oscillation would disappear. In April, they tried again, this time using multiple dams in unison.
They tried to use two power plants to stabilize the third in order to push past the oscillation barrier. That approach yielded slightly more generation. Later, they turned on two 8 MW units with load divided evenly between the two.
Testing different settings for the operational controls, they traded some efficiency for stability, and the units cruised through the barrier and generation was stable. The only limit was the ultracapacitor's 8-MW limit.
The water level did not affect the test. Streamflow during the successful test was substantially lower than it was during the unsuccessful 2017 test.
The water columns feeding the turbines in the dams have different dimensions, so they oscillate at different frequencies. It appears that by working together, one is able to stabilize the other until both are past the oscillation barrier, Jenkins said.
INL is analyzing data collected during the test and from other sources. Analysis of the field test should be published by the end of June.
The goal is to enable other hydropower facilities to function as blackout backstops. Using the field test data, INL will run scenarios to determine how to replicate it at other dams. That study could be published as soon as this fall, INL's Mosier said.
"Those are plants for which this technology could be deployed today," he said, noting that there are several thousand small hydropower plants around the country.
Thousands more unpowered dams could be retrofitted, adding further resiliency to the grid. Furthermore, irrigation modernization, another of Mosier's research areas, is another source of potential capacity. In Hood River County, Ore., irrigation water is also used for hydropower generation, providing enough power to keep emergency services going during an outage, according to a KGW-TV news report.
Resources such as these can help communities that could lose power during wildfires, cyberattacks, major earthquakes or other extreme events, he said.
The field test proved the concept that small hydro can be used to create microgrids and even help bring the grid back on line, Jenkins said.
Idaho Falls Power has identified emergency response facilities to ensure they have power if the grid went down. The utility's 50 MW of hydro capacity is only a third of the city's 150 MW peak load.
"I'm slightly less scared now," Jenkins said.