In the hours before the nation's worst blackout (search), several transmission lines in Ohio were carrying massive amounts of power "well above" emergency summer standards, a company that owns the lines said Friday.

American Electric Power owns or co-owns the power lines with FirstEnergy Corp., (search) which is at the center of a U.S.-Canada blackout investigation. The company released the information with a timeline but didn't offer any conclusions about the cause of the outage.

AEP said it avoided potential widespread outages in its area -- only 14,000 of its customers lost power -- because automatic control systems detected "abnormal operating conditions" and tripped -- or disconnected -- from linked FirstEnergy lines.

"It is likely that the automated controls tripped some transmission lines moments before they would have burned down because of extremely high power flows out of our system," said Henry Rayne, AEP's executive vice president.

The power outage darkened homes and businesses in eight states and parts of Canada, affecting 50 million people. It shut down more than 100 power plants and knocked Cleveland's water supply off line.

Investigators have pointed to three transmission lines owned by FirstEnergy in northern Ohio that shut down Aug. 14 as the possible cause.

The heavy load of power on the lines occurred after FirstEnergy's Eastlake power plant tripped off line at 1:35 p.m., about two hours before the cascading blackout began, says AEP's timeline and one released by the North American Electric Reliability Council.

It remains unclear if FirstEnergy did something to cut back on demand after losing electricity generated by the Eastlake plant. If not, FirstEnergy would have had to use power generated from other utilities to serve its customers and keep exporting power -- which could have caused surges and overload lines, according to utility experts.

"Simply losing a generator is enough to overload lines, if there weren't steps taken to interrupt demand," said Robert Burns, senior research specialist at Ohio State University's National Regulatory Research Institute (search). "The other companies may not at the time have known what was causing this," Burns added.

American Electric Power said in fact that power was being siphoned out of its territory, apparently boosting the amount of electricity carried over its lines.

"A number of the lines were carrying power flows well above the summer emergency rating for the lines because of the massive amounts of power being drawn north from AEP's system," the company said in a news release Friday.

AEP said its first failure came at 3:45 p.m. in a line it co-owns with FirstEnergy that comes from a Canton substation. AEP said the line was "abnormal" for 58 seconds. That was more than two hours after the problem at the Eastlake plant.

A Canton Center-Cloverdale line, for example, had a summer emergency rating of 197 megavolt-amperes, but was carrying 332 megavolt-amperes when it tripped, the company said. The East-Lima-Fostoria line tripped at 2,000 megavolt-amperes, much higher than its summer emergency rating of 1,383, AEP said.

The blackout peaked across the Midwest and Northeast at 4:11 p.m.

The company said it was providing the data to the North American Electric Reliability Council (NERC), which is helping in the investigation led by the U.S. and Canadian governments, which took over the probe last week.

Meanwhile, a preliminary report compiled in May by the Public Utilities Commission of Ohio said AEP had skimped on its capital improvement budget and reduced tree-trimming in the past decade in its rural service areas.

The report focuses only on the distribution lines to homes and businesses, not the high-voltage transmission lines that are the focus of the blackout investigation, commission spokeswoman Shana Gerber said Friday.

Customer complaints highlighted in the report were in north central and southeast Ohio. The blackout investigation centers on northeast Ohio.

The Columbus-based company generates the most electricity and owns the most transmission lines in the nation.

AEP had not yet responded to the report's recommendations, which included expansion of tree-trimming, Gerber said.

The company said Friday that it had increased maintenance spending and had not yet verified the PUCO report.

"There have been no claims by regulators or government officials about the performance of AEP's transmission system or actions by the automated protective transmission control systems related to the Aug. 14 blackouts," AEP said.

Even before last week's blackout, federal regulators were keeping close tabs on the way power is managed in the Midwest.

The Federal Energy Regulatory Commission has been on site monitoring the Midwest Independent Transmission System Operator since May. The Midwest ISO began operating less than two years ago, overseeing the Ohio utilities that failed.

Industry watchdogs also have targeted the electrical transmission system in the Midwest for scrutiny, saying regulators needed to improve communications to prevent problems when unusually large power swings run through the lines.

Yearly reviews by NERC routinely warned that area managers needed to closely supervise the lines carrying power between generators and eventually onto customers.