Frequency swings caused island-wide power outage – The Garden Island

LIHU‘E — All 35,091 members of Kaua‘i Island Utility Cooperative were affected by a power outage late last month, with the first power restorations beginning 18 minutes after the outage occurred.

The outage was due to frequency swings on the power grid, according to KIUC Chief of Operations Brad Rockwell.

Frequency refers to the amount of electricity running through a power grid. Most U.S. grids run on a frequency of 60 cycles per second (60 hertz). Deviations in that pattern can cause problems for electrical equipment assigned to the power grid.

Rockwell explained the April outage happened when the KIUC grid was operating at 100% renewable energy. When that happens, it is slightly more susceptible to problems. The work that KIUC has done over the past few years to enable 100% renewable operation helps KIUC to overcome these problems without any customer impact most of the time.

“For this particular outage, the system began experiencing severe frequency swings, possibly due to renewable generators being out of sync,” Rockwell said.

“Attempts to stabilize were unsuccessful, and the grid eventually went black. Although we are still diagnosing the incident, we’ve already made adjustments that will better alert us should similar conditions occur so we can stabilize and avoid loss of power.”

According to Rockwell, frequency is a unit of measurement that electric utilities use to monitor the stability of systems. Utilities maintain the frequency of their electric system within narrow ranges, and make adjustments to ensure that frequency doesn’t reach a level which can damage equipment. “Frequency swings” refers to movement of frequency within the operating range.

“If system frequency moves to the outer ranges of the acceptable band, our system will disconnect customers and our generators will shut down,” he said.

Rockwell said the protection devices began to operate at 1:38 p.m., and all customers were without power at 1:45 p.m.

“Approximately 50% of customers were restored within 45 minutes, and all members were restored within one hour and nine minutes of the outage occurring,” Rockwell said.

Rockwell noted that the outage was very different from the one in 2019, which was caused by an electrical fault at one of KIUC’s conventional (oil-powered) generators.

“This outage had nothing to do with our conventional generators and, in fact, this equipment was instrumental in restoring power quickly,” Rockwell said.

“Fortunately, KIUC has a robust data infrastructure and access to highly-detailed information about what was occurring on the grid when the outage occurred. This allows us to diagnose what happens and make necessary adjustments so that we can prevent a similar occurrence in the future.”

Rockwell said KIUC’s grid is unlike any other grid in the world because it runs for multiple hours a day at 100% renewable generation. KIUC has operated the grid at 100% renewable for thousands of hours over the past 18 months. The shift to using 100% renewable energy has has resulted in tens of millions of gallons of fuel that are no longer shipped to the island every year. Additionally, that fuel is no longer burned, and the emissions no longer go into the air.

And reliability, according to the statistics, is usually pretty good.

Kaua‘i had the best electric reliability in the state for three of the last five years, with 2020 being the best ever since the entity became a co-op in 2002.

“That being said, there will be issues to be addressed and lessons to be learned along the way,” Rockwell said.

“The fact that our power-generation team was able to bring the grid from completely black to full output in just over an hour is an incredible accomplishment, and a testament to their technical skill, resourcefulness and commitment to our members. While there are inevitable growing pains with shifting to 100% renewable energy, we must recognize the significant benefits it provides for Kaua‘i.”

Some of those growing pains include the fact that the electrical grid has become dominated by inverter-based resources like solar and batteries as opposed to conventional generators, which operate with rotating equipment such as turbines, or KIUC’s generators at Port Allen currently running on diesel.

“Inverter-based resources respond differently to frequency changes than conventional units, and our grid operations are continually adjusting to reflect the different equipment mix supplying the island,” he said.


Stephanie Shinno, education and business reporter, can be reached at 245-0424 or


May 16, 2021 susan ward