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Ride the surprisingly slow Electron Express

By Theresa Cook,2014-12-12 00:43
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Ride the surprisingly slow Electron Express

Ride the surprisingly slow Electron Express

    Wouldn’t it be fantastic if we could travel at the speed of an electron? Imagine a trip from The Dalles, Ore., to Los Angeles in the blink of an eye on the 846-mile Electron Express known as the Pacific DC Intertie.

    Unfortunately, you would be in for a disappointingly long ride.

    Incredible as it may sound, the electrons themselves make a rather leisurely journey. To travel on the DC line from Celilo Converter Station near The Dalles to Sylmar Converter

    Station near Los Angeles would require hundreds of years. Assuming the line operates at full power, had you hitched a ride with the first group of electrons that left Celilo in 1970, when the line was energized, your Electron “Express” would reach southern California about the year 2912 at the earliest!

    How can this be? When we flip a light switch, the bulb turns on immediately. Doesn’t electricity travel at the speed of light?

    Yes and no. When the switch is turned on, a voltage is applied to the circuit that propagates

    along the wires at nearly the speed of light. The entire chain of electrons is set in motion

    this is the current causing the bulb to shine “instantly.” But while the electrons respond immediately to the electromotive force and begin to accelerate in unison through the wire, their motion is impeded because of repeated collisions with individual atoms that make up the wire. As a result, the electrons move remarkably slowly less than a millimeter per second,

    roughly the speed of a snail.

On the DC line, when a voltage is applied Celilo Converter Station

    to the circuit at Celilo, the electrons along

     the entire wire start moving nearly

    instantaneously, including those at

    Sylmar. In this way, energy is delivered to California at light speed, although the electrons themselves are moving very slowly.

    So back to our Electron Express: those poor, pitiful electrons that left Celilo in 1970 might just now be reaching the 36-mile mark, somewhere near Maupin, Ore. Given this laborious and incredible journey, maybe that’s where BPA should have held its 40-year DC intertie

    anniversary celebration this past year!

    DC versus AC current

    What is “DC,” or direct current? It is an electric current (flow of electrons) that travels in one direction around a circuit loop.

    In a flashlight battery, electrons flow from the negative () terminal through the bulb and

    back to the positive (+) battery terminal. On the DC intertie, electrons travel southward over one of the two conductors to Sylmar, where conversion equipment extracts energy from the circuit and feeds it into the California grid. From Sylmar, the electrons continue their journey back north to Celilo on the other conductor, completing the circuit.

    With AC “alternating current” electrons reverse direction periodically. Most power systems in the world are AC. In the United States, a complete reversal of current direction occurs 60 times each second, hence the familiar terms “60 cycle” or “60 Hertz.” The electrons move first in one direction, then reverse course, making one complete back-and-forth motion every

    th1/60 of a second. So, while the electrons in a DC circuit eventually move on down the line, however slowly, the electrons in an AC circuit just jiggle back and forth and never really go anywhere, like high school kids at a school dance.

     (In Europe, 50 Hz is the standard frequency. There is no significant inherent technical advantage of using 60 Hz over 50 Hz. In the U.S., 60 Hz was chosen because it worked slightly better with early electric-arc lighting systems; in Europe, 50 Hz was thought to be

    more “metric.”)

    Which is better DC or AC? There are pluses and minuses to each type of circuit. Which delivery method makes more sense depends on the specific circumstances. To move large

volumes of power over great distances nonstop, DC is often the more economical and efficient

    method. The lower power losses of the Pacific DC Intertie compared to an equivalent AC line outweigh the disadvantage of the costly equipment needed to convert AC to DC and back to AC. But for transmission of bulk quantities of power over shorter distances within a regional

    grid or for interregional transmission with substation off-ramps to serve local loads along the

    way, AC circuits are usually the better choice.

    Either way, slow electrons transfer energy fast

    The fact that electrons travel slowly along a wire is more of an intellectual curiosity than

    anything. In practice, it’s not their motion that makes electricity so miraculous, it’s what they

    can do facilitate the transfer of energy almost instantly.

    When you “demand” energy at home or in your office, all you have to do is flip a switch. The

    power generator responds immediately, and energy it produces is transmitted over the circuit at light speed to where you need it.

    Rodney Aho received the B.S. degree in physical science and education in 1973 and M.A.T. degree in physical science in 1978 from Washington State University, Pullman, Washington. From 1974 to 1978, he was a science instructional technician in the Department of Physics at WSU. From 1978 to 1980, he worked for Columbia Basin Electric Cooperative, Heppner, Oregon. He has been with the Bonneville Power Administration since 1980 and is currently a public utilities specialist in Portland, Oregon. He has taught introductory physics at Embry-Riddle Aeronautical University’s Portland branch. At BPA he

    teaches courses in electrical fundamentals and power systems for non-technical staff.

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