In the 1880s, the first electrical distribution systems were designed and patented by Thomas Edison, and were based on direct current (DC), not alternating current (AC), as they are today. Edison preferred DC because it worked well with his incandescent lamps, motors, and storage batteries. In an Edison DC network, generating plants fed a mere 110 volts into heavy gauge conductors, with customer loads (lighting and motors) tapped off it.
By the time it reached the customer, the voltage would have dropped via resistance to about 100 volts, which matched the 100 volt lamps and motors at the customer’s location. Because of the voltage didn’t have far to drop because of resistance in the wires, generating plants had to be constructed within mile or so of the load. Higher voltages would have allowed the power to travel farther, but there was no efficient low-cost technology that could reduce a high transmission voltage to a low utilization voltage. In other words, there was no inexpensive “DC step-down transformer.” Lower voltages were felt to be safer anyway.
Working with rotary magnetic fields, Nikola Tesla devised an entire electrical distribution system (generation, transmission, and use) based on AC power. Tesla’s work interested George Westinghouse, who put up the money to commercialize the system.
Unlike DC, AC systems used a high voltage, long-distance distribution system (today’s lines operate at about 750,000 volts) and transformers to lower the voltage near the customer locations.
In the ensuing “War of Currents” era (sometimes called the “War of the Currents” or the “Battle of Currents”) of the late 1880s, Westinghouse and Edison battled for supremacy for their respective current distribution systems. During this time, Edison muddied his reputation by carrying out a major publicity effort to disparage alternative current.
Aside from lobbying against AC use in various state legislatures, he spread information on fatal AC accidents, and publicly killed animals with electricity, such as stray cats and dogs, unwanted cattle and horses, and finally the filmed electrocution of Topsy, an unruly Coney Island circus elephant (the elephant’s handler refused to be part of the proceeding).
Edison also attempted to popularize the term for being electrocuted as being “Westinghoused.” His preposterous shenanigans turned serious when, although opposed to capital punishment, he secretly paid Harold P. Brown to construct the first electric chair for the state of New York using AC, and to publicize that fact.
Ultimately, AC distribution won out. The turning point probably occurred when, defeating a General Electric/Edison proposal, the Westinghouse/Tesla AC system won the international Niagara Falls Commission contract to harness the power of Niagara Falls. In 1893, work began on the generation project and soon, large amounts of electric power were being generated and transmitted as AC to Buffalo, New York.
But, the downtown areas of many cities retained their old DC networks in case of emergencies, or because certain DC equipment was important enough to remain in use. (A mercury arc valve rectifier could be used to convert AC into DC.) Helsinki, Finland maintained a DC network until the late 1940s, and Stockholm, Sweden didn’t completely eliminate its DC network until the 1960s. In New York, DC was used mostly for certain elevators. In January 1998, “Con Edison” began to terminate DC service to its existing 4,600 DC customers. By 2006, there were only 60 customers using DC service, and on November 14, 2007, the last direct-current link was turned off. However, DC continued to live on in “third-rail” electric railways (500-750 volts).
In the new “Green” Age, DC has slowly been making a comeback. Computers based on DC power supplies can be pushed to yield 10 to 30 percent more performance than AC-based machines before they overheat. In 2006, researchers at the Department of Energy’s Lawrence Berkeley National Laboratory (“Berkeley Lab”) teamed with about 20 companies, include Cisco (News
), Intel, and Sun Microsystems, to demonstrate technologies in a Sun test facility in Newark, California that could save billions of dollars a year in data center energy-related costs. Instead of converting back and forth from AC to DC to power the equipment, they demonstrated that using DC entirely throughout a data center would save 10 to 20 percent in power costs and supposedly improve reliability.
Also, Validus DC Systems
, in late 2007, announced it had raised $10 million to develop data center power supplies, based on DC, to lower power consumption. Validus estimates that data centers can slash energy consumption by up to 40 percent.
Thinking on a larger scale, about 10 percent of all power sent through high voltage AC transmission lines is lost as corona discharge off of the wires. (Some is also lost because of the so-called “skin effect”.) Direct current would solve this problem to a considerable degree.
High Voltage Direct Current (HVDC) systems first made their appearance in Scandinavian countries, such as Norway, where they are used to send power through long cables across the bottoms of fjords. Modern large-scale solid-state devices enable HVDC systems to change voltages with the ease of AC systems. Of course, given that the whole world is currently powered by AC, the new HVDC networks simply connect existing AC systems. However, their voltages are easier to control than those of AC networks.
Ironically, in a recently article in Vanity Fair, Robert F. Kennedy, Jr. describes what the next President of the United States should do: “First, our regional power grids are overstressed and misaligned. The biggest renewable-energy opportunities — for instance, Southwest solar and Midwest wind — are outside the grids’ reach. Furthermore, traveling via alternating current (AC) lines, too much of that wind farmer’s energy would dissipate before it crossed the country. The nation urgently needs more investment in its backbone transmission grid, including new direct current (DC) power lines for efficient long-haul transmission. Even more importantly, we need to build in ‘smart’ features, including storage points and computerized management overlays, allowing the new grid to intelligently deploy the energy along the way. Construction of this new grid will create a marketplace where utilities, established businesses, and entrepreneurs can sell energy and efficiency.”
Perhaps Edison’s ghost may have the last laugh after all.
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