UniSource Energy Services says a power outage that affected nearly 20,000 customers in Santa Cruz County on Feb. 1 lasted much of that day for many customers because a failed power line that caused the blackout was difficult to reach.
Sabotage has been ruled out.
The outage began around 4 a.m., affecting those in Amado all the way to Nogales and causing local schools, government offices and many businesses to shut down for most of the day, as some customers didn’t have power restored until around 5:30 p.m.
UniSource spokesman Joe Barrios said the outage was caused by the failure of a conductor, or wire, on the main 138-kilovolt transmission line that serves Santa Cruz County, and its remote location made it difficult to repair quickly.
“Everyone in Santa Cruz County is served primarily by that 138 (kilovolt) line, which runs through some pretty remote and rugged terrain,” Barrios said. “It took some time to inspect the line, find the problem, access the site and get employees and materials there to begin repairs.”
UniSource Energy Services, a sister company to Tucson Electric Power Co., provides power to more than 19,000 customers in Santa Cruz County, as well as more than 80,000 customers in Mohave County.
Barrios said the utility was able to get some customers back online by mid-afternoon by using a 46-kilovolt line to energize the utility’s Valencia substation on Nogales’ north side, where the company also started up gas-fired generators at the adjacent, 63-megawatt Valencia Generating Station.
Those measures took some time though, Barrios said, noting that the 46kv line was out of service for an upgrade at the time.
UES had restored service to about 6,000 customers by 1 p.m. and by 2 p.m., 7,000 remained without power, Barrios said.
The line was repaired by about 3:20 p.m. and brought online in stages to avoid complications, with power to all but about 2,100 restored by 4 p.m. and the rest online by about 5:30 p.m., he said.
The cause of the conductor failure is still under investigation, but UNS has ruled out sabotage, Barrios said.
In 2014, a saboteur broke into the Valencia Generating Station and planted a makeshift bomb that exploded next to a valve assembly on a 50,000-gallon diesel fuel tank but the tank did not detonate. The FBI investigated but no arrests were reported.
Because of the outage’s magnitude, UES will be required to file a report on the incident with the Arizona Corporation Commission, Barrios said.
UES has improved its system reliability rankings in recent years and for the past four years has been in the top quartile for reliability among power companies across the nation, Barrios said.
The systemwide average time UES customers were offline during power outages in 2021 was about 48 minutes, up from 43 minutes in 2020, and down from a three-year average of 50 minutes from 2019 through 2021.
In November, UES filed a rate case with the Arizona Corporation seeking a 14% bill increase, seeking to recover some $78 million in system improvement costs since 2019.
Last year, UES installed a mobile substation next to its Sonoita Substation in Rio Rico to quickly add capacity and meet summer demand peaks.
Here are a few ways to keep your food safe to eat in the fridge and freezer during a power outage.
