Canada’s natural gas processor and utility company AltaGas Ltd. said that it will buy three gas-let go electric power plants in California for US$642 million from a fund keep running by Oaktree Capital Group. Calgary-based AltaGas said it agreed to buy GWF Energy Holdings LLC, which claims the three utilities, from Oaktree Capital’s infrastructure venture centered Highstar Fund IV. They generate a joined 523 megawatts of power and are situated in the San Joaquin towns of Hanford, Tracy and Lemoore. AltaGas Power Holdings is buying GWF Energy Holdings LLC, the plants’ proprietor, from Highstar Capital IV LP. The deal is…