Entergy Corp. said Wednesday it has completed the previously announced purchase of the Rhode Island State Energy Center, a 583-megawatt power plant in Johnston, R.I., for approximately $346 million.

The natural gas-fired power plant has been operating since 2002 and a recent upgrade increased the plant’s capacity to 583 megawatts from 550 megawatts. The plant supplies enough electricity to power about 500,000 homes in the New England market.