Entergy's transmission system has sustained extremely severe damage from Hurricane Gustav, damage that could make power restoration a difficult and slow process, especially in southeastern Louisiana.

In terms of power outages, Hurricane Gustav was the second worst in Entergy's 95-year history, peaking at about 850,000 early Tuesday -- the overwhelming majority of them in Louisiana. That easily bypassed the 800,000 outages in Hurricane Rita in 2005. As of 4 p.m. CDT, more than 795,000 Entergy customers were still without power. Nearly 55,000 customers whose electrical service was disrupted by Hurricane Gustav have been restored. The only larger number of Entergy outages was 1.1 million in 2005 during Hurricane Katrina, which has been described as one of the worst natural disasters in American history.

Thirteen of the 14 transmission lines serving the New Orleans metropolitan area are out of service due to the storm. This creates a situation where the New Orleans metropolitan area and a corridor along the Mississippi River between New Orleans and Baton Rouge have become essentially an island, no longer electrically connected to the rest of the Entergy system and the electricity grid for the eastern United States. This "island" is south of Lake Pontchartrain and includes Orleans, Jefferson, St. Bernard, St. James, St. John the Baptist, St. Charles and upper Plaquemines parishes, which are sometimes referred to as the "river" parishes. Entergy's Waterford 1, Nine Mile Point and Little Gypsy plants are now supplying all power to this zone because all transmission lines leading to and from there are out of service.

"Entergy's preparations made in advance of the storm to protect its systems contributed directly to the power that is still on in New Orleans," said Gary Taylor, Entergy's group president, utility operations. "Without the planning to isolate some generators, this transmission damage would have interrupted power everywhere in the New Orleans area."

Part of the difficulty is that there are no transmission lines to the south of New Orleans area because of the Gulf of Mexico. Transmission lines to the north, east and west are out of service. Transmission lines in the Baton Rouge area that are needed to tie the "island" back to the system are out of service due to severe storm damage there. Continued bad weather is preventing damage assessment by helicopter at this time, which is delaying returning the system to service.

Service restoration to emergency facilities in the affected area continues. Other restoration continues, but energizing of completed repairs will be delayed until the area can be tied back to the rest of the system. This is being done to maintain the level of electric demand and prevent it from exceeding the available generation in that area. If load grows too high, the generation could trip offline, causing the entire area to lose power until generation within the island could be restored.

"Restoration organizers are assessing how to best tie and synchronize the area back into the Entergy system. This will be a very delicate operation requiring close coordination among generation, transmission, distribution and other Entergy functions," Taylor said. "The greatest risk at this time is that generation in the islanded area could trip offline before Entergy is able to tie back to the Entergy system. If the islanded generation goes offline, all power in the 'island' zone could be lost."

There is a slight possibility that connecting the islanded area to the rest of the system could cause the islanded area to trip offline. If so, it could be several more hours before power could be restored to the area and it is tied to the rest of the system.

Entergy has experienced extensive distribution system damage, as well. This damage will be repaired in parallel with the transmission repairs so distribution will be ready as soon as possible when the transmission system repairs are made.

It is not yet possible to estimate when electricity will be restored to specific locations. In some areas where the damage is the most extensive or where access is the most difficult, restoration could take several weeks.