About 1,300 Alliant Energy customers in Portage were without power Monday night when the company's energy distribution system sensed a problem and shut down temporarily.

Alliant Energy spokesman Steve Schultz said the power outage was reported around 8:50 p.m. Monday and lasted until 9:35 p.m., mostly on the city's east side.

Schultz said crews have yet to determine the cause, and the company is still investigating. There were no storms in the county Monday night.

According to Alliant Energy's Web site, when an object or weather causes a power line to short circuit, a self-resetting breaker called an automatic reclosure is activated, which is what happened Monday. The reclosure stops the flow of electricity momentarily to allow the object to clear itself of the line. If the object does not clear itself from the line, the reclosure will activate again - up to three times.

After that, if a fault is still present on the line, the reclosure will lock out and cut off the power until the problem is manually corrected by Alliant Energy personnel.

The most frequent causes of power blips are lightning strikes and trees interfering with the lines.