NEW YORK, Sept 4 (Reuters) - More than 690,000 customers in Entergy Corp's (ETR.N) service area in Louisiana, Arkansas and Mississippi remained without power Thursday morning after Hurricane Gustav caused massive damage to the company's transmission system when it hit Louisiana Monday.
Gustav cut power to more than 1.8 million homes and businesses along the Gulf Coast, and shut more than a dozen oil refineries and numerous oil and natural gas pipelines and other energy facilities.
Entergy said it could be several weeks before it restores power in the hardest hit areas.
Hurricane Gustav caused the second largest number of outages in the company's 95-year history behind only Hurricane Katrina, which left 1.1 million out in 2005.
At the peak Tuesday morning, about 850,000 Entergy customers were without power primarily in Louisiana and Mississippi. Since then, workers have restored service to some customers while others have lost power as the storm moved inland. About 93,000 customers lost power in Arkansas on Wednesday.
Elsewhere in Louisiana, Cleco Corp (CNL.N) of Pineville said about 155,000 customers were still without power, down from over 240,000 on Sept. 2. That peak was about 90 percent of 273,000 customers Cleco serves.
Damage to Entergy's transmission system included 191 transmission lines and 210 substations out of service.
The New Orleans and Baton Rouge area is essentially an island, no longer connected to the rest of the state's power grid, Entergy said.
The 400 MW Waterford 1 natural gas/oil-fired unit, the 1,804 MW gas/oil-fired Nine Mile Point station and the 1,204 MW gas/oil-fired Little Gypsy station were supplying all of the power to New Orleans and Baton Rouge.
Entergy shut the 967 MW River Bend nuclear power station in Louisiana Monday afternoon due to the loss of demand caused by extensive outages in the region.
Before the storm hit, Entergy shut the 1,152 MW Waterford 3 nuclear power reactor in Louisiana Sunday night in anticipation of the heavy winds forecast.
Both nuclear reactors remained shut Thursday morning.
One MW powers about 500 homes in Entergy's service territory.
Entergy, of New Orleans, owns and operates about 30,000 MW of generating capacity, markets energy commodities, and transmits and distributes power to 2.7 million customers in Arkansas, Louisiana, Mississippi and Texas. (Reporting by Scott DiSavino; Editing by John Picinich)