A utility company spokesman says a power substation that failed and caused a blackout in San Francisco had been set to be part of a $100 million upgrade.

Pacific Gas & Electric also said Friday that power had been restored to all but 3,000 of the almost 90,000 customers hit by the outage.

Spokesman Barry Anderson said the outage was a "case where the equipment failed before we could get to it."

He said something went wrong with a circuit breaker that made it explode but the utility isn't sure yet what happened.

The outage left people in the dark in the Financial District and other parts of the city.  Officials said no injuries were associated with the incident.