A problem at Xcel Energy’s Rifle substation caused a power outage across much of western Garfield County Monday.

Power had yet to be restored to some residents as of late Monday night.

The outage began at 6:20 p.m. and affected residents in the Silt, Rifle, Parachute and Rulison areas.

Xcel’s Rifle substation suffered a differential lockout on a power transformer, said Holy Cross Energy system operations technician Rick Arnold.

In other words, excess electrical current was flowing into the transformer, and breakers in the substation automatically tripped and shut down the flow of power to prevent a fire, he explained.

The Xcel substation supplies power to two Holy Cross lines that serve an area south of the Colorado River from Morrisania Mesa near Parachute to Garfield Creek near New Castle.

Holy Cross spokesman Bob Gardner said the company had about 1,000 customers who lost power. Most of them had power restored by 9:30 p.m., and the rest were expected to have power by 10 p.m.

“We rerouted and switched around to get power back from our Parachute substation,” he said.

However, Xcel reported that power had still not been restored for its customers as of 9:50 p.m. Another crew had been called in to help.

Xcel described the outage as being caused by a “large equipment failure.”