Nearly 3,000 PECO customers were without electricity on Saturday afternoon after a large power outage occurred at the PECO substation near 13th and Lombard Streets in Center City, a spokesman for the electric company said.

The outage occurred shortly before 1 p.m. at the substation at Juniper and Waverly Streets.

Initial police reports said a transformer exploded at the substation, triggering a release of fire-suppression foam into the streets outside the facility. Police Chief Inspector Joseph Sullivan said police, including bomb technicians on the scene, found nothing suspicious in what occurred.

PECO spokesman Greg Smore said later Saturday that the cause of the noise and outage has not yet been determined. He said it was not certain if a transformer exploded or if anything exploded. The noise could have been a circuit breaker that popped, he said.

The foam from the fire-suppression system is not hazardous, Smore said. In total, 2,700 PECO customers lost power in the area near the substation, he said. Smore said that all power was restored by about 4 pm.

Bill Gregor, who lives on the 11th floor of a high-rise building on the south side of the 1300 block of Lombard Street, said he was working on his computer Saturday afternoon when he heard what he described as being a "large explosion," then saw a bright light.

"I was sitting here peaceful at my computer, then you hear a 'Kaboom!,'" Gregor said, adding that he quickly unplugged his TV and computers. He said he was at first nervous about what happened.

Firefighters who responded to the scene washed away the foam from Juniper Street.

- Julie Shaw and Rebecca Heilweil