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Return of electrical technology previously pioneered by Thomas Edison

The growth in renewable energy away from urban or industrial centers is encouraging a return to direct current

Long high voltage direct current (HVDC) kV in Canada. Source: Tonyglen14.
Long high voltage direct current (HVDC) kV in Canada. source: Tonyglen14.

By Annie Sneed, the article is published with the approval of Scientific American Israel and the Ort Israel network 20.08.2017

More than 100 years ago, Nietzsche Debate Between scientists and heads of industry on the electric grid that will be built in the USA: should it be based on alternating current (AC) or direct current (DC)? Both methods are used to transfer energy, the direct current constantly flows in the same direction, while the alternating current changes its direction cyclically. Thomas Edison advocated direct current and even publicly electrocuted stray animals with alternating current to convince the public of the danger involved. But in the early 20s, the balance was tipped in favor of the exchange rate due to technical and economic reasons.

Now the direct current is back in the arena. In the coming years, several direct current transmission lines scattered here and there across the United States will be joined by at least nine long high-voltage direct current (HVDC) lines that several companies plan to retire.

This is mainly due to two trends: the Midwest and other regions of the US today produce a large amount of renewable energy - about 2.8 trillion kilowatt hours as of 2015 - and the electricity companies need the means to transfer it to urban centers and distant industrial centers. "There are remote resources, and there is simply not enough infrastructure to transport the energy to the market," says Wayne Galli, VP of Engineering at Clean Line Energy Partner, which plans to build four high-voltage direct current lines. The company, headquartered in Houston, has already sent teams to the field to prepare for the retirement of one of the lines - it will carry wind energy over 1,160 kilometers from Oklahoma and North Texas to Tennessee and Arkansas, and from there to other nearby states.

The technology for transmitting voltage was perfected in the 70s, which allows the return of direct current to the arena as a viable option - and on lines that exceed 500 to 800 kilometers in length, direct current is better than alternating current. Since from a certain length, AC systems become more expensive to set up than DC systems due to problems such as greater resistance. "The use of direct current lines is a much better solution for transferring energy from distant wind or solar farms," ​​says Gregory Reed, head of the University of Pittsburgh's "Energy Center" and "Electric Grid Institute". "Our sources of resources are changing at a rapid pace."

And since the renewable energy will not disappear in the near future, the direct current will not disappear either. And as Gali says: "The direct current has never completely disappeared".

12 תגובות

  1. Alternating current needs fewer transmission lines for the same power since the current returning to the power company (the neutral line) is zero (the twinning of the phase currents takes care of that). In direct current, the returning line should also carry a lot of current...
    Therefore alternating current is much cheaper to conduct.

  2. Isn't it worth going back to direct current at home today?
    That is, many houses can install solar panel systems that produce direct current.
    Today, the current is converted to alternating current using a very expensive converter so that it can be sold to the electricity company.
    Even using current at the home level requires, in my humble opinion, a conversion to alternating current, because that is the current that household appliances are designed to receive.
    Isn't it better, in some cases, to leave the current as a direct current and use it in the houses - as a direct current?
    I know this means that many appliance manufacturers will have to change their appliances, but I don't think it's a complicated problem.

  3. It is not resistance that is the problem, but the capacitance and inductance in long lines. Both of these components are "transparent" to direct current but cause repeated waves and energy loss in alternating current. In any case, change the voltage to large values ​​to reduce ohmic losses.

  4. A. Ben Ner
    In principle, the energy losses in ohmic resistance are the same for direct current and alternating current, for the same resistance.
    P = I^2 * R. But, and here you are right, Ohm's law is only an approximation, because for various reasons, the resistance to the current depends on the frequency (alternating current moves in the sheath of the conductor, so the effective cross-sectional area is smaller, and there are other phenomena of induction and capacitance).

    Alternating current has a difficult problem of coordinating lines with different current, which requires complex control systems. On the other hand, alternating current is easier to switch. In direct current, you can make do with fewer lines for the same power, which is a huge advantage.

    Today, direct current conversion systems (as well as rectification and inversion systems) are extremely efficient, and did not exist in the time of Edison and Tesla. Edison planned to build local power plants and thus save on the transportation of electricity - and in the end what decided in favor of Tesla and Westinghouse (even then they didn't want smoking power plants inside cities).

  5. The energy losses due to ohmic resistance, along the conductive lines are smaller in alternating current than in direct current.
    What is claimed in the article, but unfortunately not explained, is that, in long transmission lines, over 500 to 800 km, it is necessary to establish complex systems that cost more with alternating voltage than with direct voltage.
    To me it sounds very strange and unbelievable.
    The energy losses in direct current are huge, what's more, the voltage is originally created as an alternating voltage and must be rectified before it is transmitted and distributed in the lines.
    In short - not clear.

  6. Alternating current and direct current both travel through the best conductor. In the case of the body it is its surface.

    The problem with direct current is that it causes the water in the body to break down into atomic oxygen and hydrogen. The result is fatal.

    An electrical current passes through the heart only if the heart is on the shortest conductive path to earth.

  7. Nikola Tesla is being wronged again?!?
    The man died knowing that history would not remember him as the one who signed the current exchange system - and it's a shame!
    We all owe it to him that at least his name will be mentioned in articles like this!
    Disappointed engineer

  8. I will expand because it was not explained in the article.
    Alternating current by itself has no advantage. Its advantage is the ease of raising the voltage by transformers, which is necessary for transferring over long distances, and the ease of lowering the voltage back for use.
    The technology of voltage conversion by electrical components has improved a lot, who remembers the old and heavy power supplies we used to have?

  9. 123
    You're right. Alternating current flows in the material envelope, so the current through the heart is smaller.

    Edison claimed otherwise because he wanted to sell something…

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