The power went out around 2:51 a.m. Monday and was restored at 4:59 a.m., said Mark Stutz, an Xcel spokesman.

Boundaries of the outage ran from Sixth Avenue to Alameda and Santa Fe to Peoria, the same area that lost service last month.

"This is the same general area affected by the Harrison substation fire," said Stutz.

But he said the outage is not because of a failure at the substation.

"There has been no significant event at the substation at this time. This appears to be some of type of a transmission-related event that is feeding power to that substation" said Stutz.

However, given the expected heat on Monday, Xcel Energy is again asking residents and businesses in that area to conserve energy. The affected area is bounded by Havana Street, Alameda Avenue, Interstate 70 and Santa Fe Drive in Denver.

On June 7, a transformer bank at the Harrison Substation, located at 14th Avenue and Jackson Street, exploded. Power was knocked out to at least 31,000 customers in east Denver.

The Harrison Substation is back to about 85 percent of its original capacity but equipment at the substation is temporary and will be so until two, permanent replacement transformers can be put into service, later this year or in early 2011, Stutz said.

"Given that there is a temporary transformer and portable substation at Harrison, we do not anticipate the need for controlled outages, but conservation efforts will help ensure this," Stutz said.

During Monday's outage, police officers were posted at a number of intersections because the street and traffic lights were out.

Meanwhile, the traffic lights at the intersection of Colorado Boulevard and Cherry Creek Drive South are all out, in all four directions, and causing a huge traffic backup. Stutz said the problem is due to an underground cable which affects just that signal. Because crews have to dig up the cable to fix it, it could take up to four hours to fix, he said. The light may not be fixed until noon.