Why Did Hurricane Sandy Knock Out New York City's Power Grid?

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Though much of New York City has mopped up the damage left by Hurricane Sandy, many areas are still struggling to get back on the grid and return to normalcy. Residents of New York City public housing buildings affected by Hurricane Sandy are finally getting the lights back on more than two weeks after the storm struck, though many of these are still without heat and hot water.

Most of the 2.1 million people that lost power in the storm have their lights back on. But on hard-hit areas of Long Island, there are still some 28,500 people without power.

On Tuesday, New York Governor Andrew Cuomo opened up an investigation into how utility companies responded to Sandy. The commission formed by Gov. Cuomo will also examine the roles of various state regulatory agencies and quasi-governmental bodies in the state of the Empire State's utility system.

"I believe the silver lining on this storm can be that the Legislature understands we need to seriously overhaul the energy regulatory and power distribution in this state," Cuomo said at a press conference Tuesday.

Also on Tuesday, the chief operating officer of the Long Island Power Authority, which serves the storm-ravaged Rockaways, announced his resignation. Michael Hervey, who was also serving as acting chief executive officer, said he had been looking to step down for some time, according to Newsday. But his exit does coincide with LIPA's admission that it fell behind on routine tree trimming around power lines, which has prompted condemnation from Gov. Cuomo and New York City Mayor Michael Bloomberg.

To understand how a storm can cause such widespread power outages, it's probably best to first understand how electricity gets from the power plant to your wall socket.

Electrical power flows from a power plant to transmission substations, which crank the generated voltage even higher to transmit the energy over long-distances -- somewhere between 155,000 and 765,000 volts. The high-voltage transmission lines look different than the wooden poles you may be more familiar with, as they run through large steel towers.

However, the high voltage has to be brought down lower once it reaches the distribution grid -- the average home or business can't handle hundreds of thousands of volts, nor does it need that much power. So the high transmission lines run into power stations, which bring the voltage down and send the power in multiple directions.

When power gets closer to your home or business, typically it runs along a wire attached to the more familiar set of wooden poles, or else those lines are buried underground (as they are in Manhattan and in many parts of New York City's outer boroughs.) The poles have transformer drums that further reduce the voltage down to the normal 240 volts that a household uses. Your house also has safety devices like fuses designed to overheat and kill the power to a wire if something goes wrong, and circuit breakers that detect problems and shut off the flow of electricity.

So, as you can see, there are multiple points at which this system can be disrupted by a storm. Power lines can be knocked down, substations may go out, and transformers may blow, as one did at a ConEdison plant on 14th Street in Manhattan thanks to Sandy. Even if power lines and transformers and substations are repaired, floodwaters have to be pumped out of basements and all the equipment checked for damage and tested to make sure it's safe to turn the power back on.

But preventative measures also played a role in the Sandy-related blackouts in lower Manhattan. The hurricane's storm surge flooded substations in Battery Park, Chelsea and the East Village, and ConEdison shut the power off in order to limit the damage the water could to do its equipment.

New York also has one of the older power grids in the U.S., hailing from the early 20th century. Manhattan's distribution lines are buried underground, but outer boroughs like Brooklyn and Queens still have above-ground lines. Above-ground lines have the advantage of being easier to access for repairs, but are then much more vulnerable to the elements.

Another vulnerability of our power grid is its fundamental structure. America predominantly runs on alternating current, or AC, instead of DC, which transmits electrical current in one direction. The main advantage of alternating current is that its voltage can be easily changed with transformers, which makes our distribution system possible. But AC power grids are more vulnerable to failure due to 'voltage crash' – since they require an equal and opposite current running to balance the system, small individual 'leaks' can bring down whole power networks.

“Basically, we already have an AC grid system much more vulnerable to voltage crash," reporter Marni Chan wrote on the blog PolicyMic, "because there are more points of weakness, a.k.a. more opportunities for Sandy to do damage."

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