Calpine/Mitsui Ontario Greenfield natgas units shut

NEW YORK, Nov 12 (Reuters) - Calpine Corp (CPN.N)/Mitsui & Co Ltd's (8031.T) 517-megawatt Unit 4 and 212 MW Unit 3 at the Greenfield natural gas-fired power plant in Ontario shut early Thursday, the Independent Electricity System Operator said in a report.

The 1,153 MW Greenfield, owned 50-50 by Calpine and Mitsui, is a combined-cycle facility located in Courtright near Sarnia, Ontario about 60 miles (95 km) northeast of Detroit, Michigan. The plant has three 212 MW combustion turbine Units 1-3 and and one 517 MW steam turbine Unit 4.

All of the other units remained available for service.

Combined-cycle technology uses natural gas to turn a combustion turbine to generate electricity and then uses the hot gas leaving the combustion turbine to heat water to produce steam to turn a steam turbine and generate more power.

One MW powers about 1,000 homes in Ontario.

Calpine started building Greenfield in 2005. It operates under a 20-year power supply agreement with the Ontario Power Authority.

In April 2007, the companies hired Emera Inc's (EMA.TO) Emera Energy Inc to buy the natural gas the plant burns and sell the power it produces.

Calpine, of Houston and San Jose, California, owns and operates about 24,000 MW of generating capacity in operation and under construction and markets energy commodities in North America.

Mitsui is a Japanese trading house that owns and manages about 3,800 MW of generation in 16 countries, among other things. (Reporting by Scott DiSavino; Editing by John Picinich)