LEWISTON — Central Maine Power Co’s $1.4 billion transmission system upgrade reached a milestone Thursday with the energization of a substation on Larrabee Road.

The $57 million substation is the first major component of the upgrade program to come online and is among the utility’s largest facilities. Its role is to take power from the New England regional grid and move it for use in Androscoggin, Franklin, Kennebec, Oxford and Sagadahoc counties.

“With this substation coming online, we’ve turned a corner, and we truly have the first piece of a stronger, smarter grid for Maine’s future,” Sara Burns, president and CEO of the utility, a subsidiary of Iberdrola USA, said in a statement.

The substation equipment includes a 345,000-volt autotransformer, the first of four for the system upgrade. The five-year project also involves the building or upgrading of 440 miles of transmission lines from Orrington to Eliot.