ADVANCE FOR USE MONDAY, SEPT. 9 AND THEREAFTER - In this Sept. 6, 2013 photo, one of Commonwealth Edison's new "smart" electricity meters in seen in North Riverside, Ill. The new meter is a wireless devices that relays information on electricity consumption directly to the utility. The new units will eliminate the need for meter readers, estimated bills, and give customers the opportunity to save money because they'll be able to track daily electric consumption online and make simple changes _ like unplugging appliances or running dishwashers at certain hours. (AP Photo/M. Spencer Green)
ADVANCE FOR USE MONDAY, SEPT. 9 AND THEREAFTER - In this Sept. 6, 2013 photo, one of Commonwealth Edison's new "smart" electricity meters in seen in North Riverside, Ill. The new meter is a wireless devices that relays information on electricity consumption directly to the utility. The new units will eliminate the need for meter readers, estimated bills, and give customers the opportunity to save money because they'll be able to track daily electric consumption online and make simple changes _ like unplugging appliances or running dishwashers at certain hours. (AP Photo/M. Spencer Green) Credit: M. Spencer Green

A tree that fell on power lines near a Unitil substation on South Curtisville Road knocked out power to some 1,600 customers in Concord and some surrounding towns for two hours Thursday.

Power was restored by about 2 p.m., according to Unitil.

A substation is a power facility that changes the voltage of electricity as it moves between high-voltage transmission lines that run long distances and lower-voltage distribution lines that bring electricity to streets and buildings.