Power was restored to more than 10,000 customers in Antioch and surrounding areas of eastern Contra Costa County after a problem at a substation caused homes and businesses to go dark Monday morning.

The power failure, centered most heavily in the southeast area of Antioch near Hillcrest Avenue south of Highway 4, lasted a little more than a half-hour, according to PG&E spokeswoman Nicole Liebelt.

Crews were still determining what caused the equipment to shut down. PG&E crews were dispatched to investigate after the electricity went out just before 9:30 a.m., Liebelt said. Power was restored at 10:06 a.m., she said.

The blackout was caused when the flow of power through the substation became uneven, Liebelt said. PG&E pumps power through the substations, and the amount of voltage departing the substation is supposed to be the same as the voltage that enters it, Liebelt said.

In this instance, the amount of power entering and leaving the substation became uneven, causing the substation to shut down, Liebelt said.

Workers were still investigating to determine what caused the flow of power to become uneven.

PG&E's power outage site map listed 10,492 people without power in Antioch, but Liebelt said that number included customers in Brentwood and Oakley and that all of the outages were not connected to each other.

Contact Rick Hurd at 925-945-4789 and follow him at Twitter.com/3rdERH.