Feb 25 Electric power company Dynegy Inc said it will form a joint venture with Energy Capital Partners to buy French utility Engie's U.S. gas-fired thermal plants worth $3.3 billion. A deal with Engie, which is expected to generate about $90 million in annual synergies for the joint venture, will help establish Dynegy's presence in the Texas ERCOT market and increase its natural gas and combined cycle fleet.