Off Goes the Power Current Started by Thomas Edison

Friday, November 16th, 2007

I had no idea that DC power was still being delivered by the electric company in NYC. Finally, Off Goes the Power Current Started by Thomas Edison:

Today, Con Edison will end 125 years of direct current electricity service that began when Thomas Edison opened his Pearl Street power station on Sept. 4, 1882. Con Ed will now only provide alternating current, in a final, vestigial triumph by Nikola Tesla and George Westinghouse, Mr. Edison’s rivals who were the main proponents of alternating current in the AC/DC debates of the turn of the 20th century.

The last snip of Con Ed’s direct current system will take place at 10 East 40th Street, near the Mid-Manhattan Library. That building, like the thousands of other direct current users that have been transitioned over the last several years, now has a converter installed on the premises that can take alternating electricity from the Con Ed power grid and adapt it on premises. Until now, Con Edison had been converting alternating to direct current for the customers who needed it — old buildings on the Upper East Side and Upper West Side that used direct current for their elevators for example. The subway, which has its own converters, also provides direct current through its third rail, in large part because direct current electricity was the dominant system in New York City when the subway first developed out of the early trolley cars.

Despite the clear advantage of alternating current — it can be transmitted long distances far more economically than direct current — direct current has taken decades to phase out of Manhattan because the early backbone of New York’s electricity grid was built by Mr. Edison’s company, which had a running head start in the first decade before Mr. Tesla and Mr. Westinghouse demonstrated the potential of alternating current with the Niagara Falls power project. (Among the customers of Thomas Edison’s Pearl Street power plant on that first day was The New York Times, which observed that to turn on its lights in the building, “no matches were needed.”)

But direct current clearly became uneconomical, as the short distances that it could be transmitted would have required a power station every mile or less, according to Joe Cunningham, an engineering historian. Thus alternating current in New York began in the outskirts — Queens, Bronx, Upper Manhattan and the suburbs.

The direct current conversion in Lower Manhattan started in 1928, and an engineer then predicted that it would take 45 years, according to Mr. Cunningham. “An optimistic prediction since we still have it now,” he said.

As some of the comments pointed out, it isn’t quite true that AC is better for long-distance transmission:

Tesla’s AC eventually won the “war of currents” over Edison’s DC because the efficiency advantages of high-voltage transmission could only be achieved at the time using the AC transformer to step up the voltage from the generator to the grid, and then step it down again from the grid to the users.

However, technological developments in the last century have enabled high-voltage DC power transmission, which can actually achieve greater efficiency and lower equipment costs in some cases, mainly long-distance runs which don’t require intermediate taps, and undersea cables.

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