* Riverstone buys Babcock's North American wind business

* Pays an undisclosed sum, to commit $400 mln to the unit

By Michael Erman

NEW YORK, June 25 (Reuters) - Energy and power-focused private equity firm Riverstone Holdings on Thursday said it acquired Babcock & Brown's North American wind energy group and its development pipeline for an undisclosed amount.

The group, which has renamed itself Pattern Energy Group LP, has more than 80 employees as well as a pipeline of over 4,000 megawatts of wind developments and power transmission projects.

Riverstone has committed $400 million to expand and support Pattern's renewable energy business, the companies said.

Hunter Armistead, Pattern Energy's executive director, said the team is "free of Babcock, which is a great thing right now."

Australian infrastructure investor Babcock & Brown, once one of the country's largest firms, has been under administration since March, after its market value plunged as the global credit-crunch hurt its debt-funded expansion model.

"It was clear we needed to find another party that was interested in investing in renewables and valued our team," Armistead said in an interview. "We found the perfect partner in Riverstone -- we have a new backer."