WINDSOR — Central Maine Power is nearing completion of a $1.4 billion power grid upgrade.

Workers on Monday are going to set a 101-foot tall transmission structure, which represents the last major piece of the Maine Power Reliability Project.

Construction began in 2010 on the five-year project – the first major update of Maine’s power grid in more than 40 years.

The project has doubled the capacity of the grid’s backbone in Maine with a new 345,000-volt transmission line from Orrington to Eliot, near the New Hampshire border. Also included are five 345,000-volt substations. All told, there are 440 miles of new transmission lines.

Iberdrola paid for the improvements – about half with cash and half through borrowing. The money will be recouped from New England electric ratepayers.