The most densely populated parts of the city, generally in Manhattan and Brooklyn, are served by underground transmission wires. These offer protection from wind and falling tree limbs that plague overhead wires and make the suburbs far more vulnerable to outages.
Underground wires, though, can flood and be more difficult to repair, especially in low-lying areas. It can be harder for workers to get to the wires because manholes flood. When water recedes, it can be harder to find problems, pull out wires and equipment, dry them, fix them, and slide them back into place.
The damage assessment could take days to complete.
To engineers like Joannes Westerink, a University of Notre Dame researcher who is working on a computer model for future New York City storm surges, this was all predictable.
"You build infrastructure too low, and you run into trouble," he said. "It's a recipe for disaster."
He said it's well known that New York City had spread to ever-lower zones in modern history. He cited Battery Park at the tip of Manhattan as a dramatic example.
Con Ed could likely have preemptively shut more networks served by the substation that exploded, but that would have meant cutting power to tens of thousands of people and critical facilities like hospitals. Even though hospitals have backup power generators, they too can fail. Generators at New York University Langone Medical Center went down Monday night, and patients were evacuated.
"You have to make the decision to shut off power to a substation very, very carefully, especially if it serves critical facilities," Mansoor said. The decision can turn into a lose-lose situation.
Despite the latest damage, Mansoor called the New York City system the most reliable in the world because it's normally well protected from weather and set up with backup equipment. That protects the city from minor disruptions and helps keep major disruptions from cascading through the city.
No system, he said, can be designed to withstand every storm, no matter how severe.
Carol J. Friedland, a Louisiana State University engineer who has studied the impact of flooding on electrical systems, said more measures should be taken to protect equipment in low-lying places. For example, sea walls can be raised, and equipment can sometimes be relocated.
"My personal opinion ... is that there should be more resilience built into these types of infrastructure, because when the power goes out, it disrupts the entire community," she said.
Massoud Amin, a University of Minnesota electrical engineering professor who has studied power outages, said the storm underscores the need to improve the nation's electric grid by stringing more high-voltage wire and using modern sensor technology to spot problems sooner, isolate damage, and speed recovery from outages.
"Our electrical infrastructure system is a marvel of engineering for the last century," Amin said. "The grid operators and the power companies are doing the best they can."
It is too soon to say if anything more could have been done to keep the New York City grid working. Under state regulations, Con Ed will be required to file a report on the outage to the New York State Department of Public Service within 60 days of power restoration. That agency's staff will evaluate how problems were handled and if improvements can be made for the future, according to agency spokeswoman Pamela Carter.
Donn reported from Plymouth, Mass., and Carpenter from Chicago. AP Airlines Writers Scott Mayerowitz and David Koenig contributed to this report.
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