Peco says it continues to investigate the cause of an incident Saturday that damaged one of two transformers at a Center City substation, shutting off power for three hours and showering a side street with fire-suppressing foam.

No fire or explosion occurred at the substation near 13th and Lombard Streets, Peco spokesman Ben Armstrong said Monday. The outage, which occurred at 12:56 p.m., caused about 2,700 customers to lose power briefly. About 650 customers were without power until 4 p.m. Saturday.

Armstrong said the transformer did flash momentarily and shut down with an audible pop, which triggered emergency systems to automatically flood the site with fire-suppressing foam. That triggered a flood of commentary on social media.

"This is much like a very, very, very large circuit breaker popping," Armstrong said.

The substation reduces power from a 66,000-volt underground transmission line to 13,000 volts, which is fed into distribution lines that supply the neighborhood.

Peco was able to restore service by routing power through other substations. The damaged substation remained out of service on Monday. One of the two transformers will require repairs, Armstrong said.

The temporary loss of the substation is mitigated by the mild weather, and demand on the electricity system is about half the load needed on the hottest summer days, Armstrong said.