Lighting up the Desert Nation

Ancient World, High-Tech

The Tohono O’odham Nation spans 4,460 square miles west of Tucson and south across the border into northern Mexico. 

In the heart of their ancient homeland and off a winding dirt road is a TOUA metering station protected by a chainlink fence. Inside is a metal cabinet that houses the SEL-T400L. The site represents a cultural juxtaposition: hidden amid an environment steeped in history is a leading-edge technology to help ensure the Tohono O’odham future.

Monsoons peak in summer, when dramatic thunderstorms called microbursts erupt over the desert landscape—most often at night—bringing rain to the parched landscape but also strong winds.

“We get some bad storms here, including a lot of lightning, which can make it challenging to provide reliable electricity to our customers,” said Darrold Hobbs, operations manager of TOUA’s electric department. “To prevent outages and blackouts, we knew we had to modernize aging equipment. I heard about Schweitzer Engineering’s new relay—that it was both fast and simple—and we decided to upgrade with it.”

That decision made TOUA the second utility in the world to use SEL’s time-domain technology for tripping line breakers. TOUA serves 3,000 customers, buys power from several outside companies, and has just 16 employees on its electric crew.

Installation of the SEL-T400L allows TOUA’s employees to spend their time and effort where it’s needed most.

“They work hard and they’re skilled, but we’re a small utility with limited resources trying to cover a lot of territory,” said Hobbs.

A disturbance on a line can mean crew members have to drive an hour and a half to isolate a fault, sometimes on washed-out roads during a monsoon storm, he added.

Part of the SEL-T400L design includes traveling-wave fault locating, a technology that can save utilities hours when searching for faults. The technology pinpoints a fault’s location to within one tower span.

The First Real-World Test

Not long after the SEL-T400L went online, an intense windstorm rolled across Tohono O’odham territory, giving the relay its first real-world test. In just over half an hour, there were seven faults, and each time the SEL-T400L tripped in under 2 ms. These events made TOUA the first sub-transmission utility to experience this relay’s unprecedented tripping speed.

“If not for this new technology, the power would have gone out and our crews would have been driving around and trying to restore it in bad weather,” said Hobbs. “Instead, it did the job so well that we didn’t even know about the disturbance until later.”

With this event, TOUA made electric transmission protection history.