Nikola Tesla’s alternating current may have “won” the War of Currents at the end of the 19th Century, but the defeated incumbent—direct-current distribution, aggressively championed by Thomas Edison—endured. As historian of technology Thomas P. Hughes observed in his influential essay on the evolution of large technological systems, the War of Currents ended “not with victor and vanquished, but with the invention of devices making possible the interconnection of the two systems.” Remnants of DC power distribution kept performing their assigned tasks for decades as the AC grid thickened around them.
In fact, a few live on to this day. One of the best examples is in San Francisco, where 250-volt DC power still flows through underground and overhead cables across the city. These DC lines peacefully coexist with their AC counterparts; you can see this mix of currents straddling utility poles in the city’s South of Market district. DC’s perseverance in that neighborhood seems fitting, for it was just a few blocks away that the tiny California Electric Light Co.—a forebear to California’s dominant Pacific Gas and Electric (PG&E)—became the first power company in the United States, and possibly the world, to supply electricity to multiple customers from a central generating station. It was in September 1879—a full three years before Edison turned on his famous Pearl Street generating station in New York City—that California Electric began burning coal, raising steam, and driving dynamos in a wooden shack at the corner of Fourth and Market streets to feed current to its customers’ electric lights.
DC-driven winding-drum elevators—the leading design until the 1930s—use a DC motor in the basement that winds and unwinds the elevator’s steel cable on a steel drum, thus lifting and lowering the car from pulleys atop the elevator shaft. DC drive was the only way to go at the time for a speedy elevator, because only DC could deliver variable-speed operation for smooth starts and stops. The DC motors were also energy efficient, capable of something that has only recently become possible with modern elevator designs: regenerating power when the elevator descends.
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