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Question about AC frequency

  1. Apr 5, 2008 #1
    Why is household AC 60hz? Is 60hz more efficient than higher frequencies, if so, why? I've searched on the internet but I can't find a good answer. Thanks in advance.
  2. jcsd
  3. Apr 5, 2008 #2
    60 Hz was introduced at the Westinghouse East Pittsburgh works here in Pittsburgh in the late 1800s. Best evidence is that Tesla (who actually invented most of George Westinghouse's inventions) wanted 60 Hz for some unknown reason and Westinghouse saw no reason to go against his "golden goose". Other frequencies would have worked OK.
  4. Apr 5, 2008 #3


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    Higher frequencies do lead to slightly higher losses, but there is no realn reason why you couldn't use 35 Hz or 127 Hz instead of 60 Hz. Note that most of the world uses 50 Hz.

    However, think about how electricity is generated; most types of power plants use a turbine driving a generator at some stage
    I am guessing that the 50-60 Hz is a rather convenient frequency range for a generator in a power plant, it means that you can generate electricity (at least in principle, modern plants are presumably more complicated) by having a turbine driving a shaft (via a gearbox) rotating at a 3000-3600 rpm which is similar to the kind of RPM you get in an engine.
  5. Apr 5, 2008 #4


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    Higher frequencies more losses on long distance transmission but have smaller and more efficent transformers - aircraft system typicaly run at 400hz.

    The 60Hz system was used in America first by Telsa, originally at 220V then reduced to 110V for safety.Power wasn't transmitted long distances in those days, in fact the first power line form Niagra falls ran at 25Hz and was converted to 60Hz when it reached the city.

    Europe chose 50Hz and then increased the voltage to 220V to make up for the poorer efficency.
    The UK originally used the most efficent combination 240V at 60Hz but then switched to 50Hz to be in line with the rest of Europe.
    Last edited: Apr 5, 2008
  6. Apr 5, 2008 #5


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    From a safety standpoint 60Hz is a terrible frequency to use in people's houses. Nerves are very easy to stimulate at 60Hz.
  7. Apr 5, 2008 #6
    60 cycles per second
    60 seconds in a minute
    60 minuets in an hour

    I guess whoever standardized it just thought it sounded good.
  8. Apr 5, 2008 #7
    Real possibility. Tesla was nutty as a fruitcake.
  9. Apr 5, 2008 #8
    the most brilliant fruitcake EVER
  10. Apr 5, 2008 #9
    It is extremely interesting to me that

    60hz is an octave of the lowest "theoretical" schumann frequency (7.5hz) which I theorize is actually related to a property of Iron, and core of the earth (i.e. electromagnetic hysteresis)

    This would explain the 'performance' benefit of 60hz as well, since most transformers are made of iron.

    What do you guys think? Just a coincidence?
    Last edited: Apr 6, 2008
  11. Apr 5, 2008 #10
    There is no performance benefit specifically for 60 Hz in transformers. There is a general range, perhaps 40-100 Hz that works well with the cores normally used, but you need to remember that the silicon steel followed the electrical industry not the other way. If you look at the original Westinghouse arguments, it is clear that they could have used 50 Hz, 56.67 Hz, or 66.67 Hz; the motor speed was the critical factor. Now why 60 out of those numbers? Probably Greek mysticism.
  12. Apr 5, 2008 #11
    There is a benefit with transformers at higher frequencies...the transformer is not required to be as large. Indeed military power supplies (at least british ones) use high frequency so that the transformers etc are smaller, lighter and more easily transported.
  13. Apr 5, 2008 #12
  14. Apr 6, 2008 #13


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    60 is useful for some electric clocks that use synchronous motors.
    I visited an electric power plant once, and they had one engineer whose job was to keep the frequency as close to 60 as possible. This is not easy as the load varies. They said it was important for use in synchronous equipment.
  15. Apr 6, 2008 #14
    Similar thread: https://www.physicsforums.com/archive/index.php/t-53692.html

    Here is a somewhat related article from Wiki about television refresh rates..

    From Wiki: http://en.wikipedia.org/wiki/Refresh_rate

    "When the cathode ray tube was developed in the 1920s, technology limitations of the time made it difficult to run monitors at anything other than a multiple of the AC line frequency used to power the set. Thus producers had little choice but to run sets at 60 Hz in America, and 50 Hz in Europe. These rates formed the basis for the NTSC (60 Hz) and PAL & SECAM (50 Hz) sets used today. It was widely perceived that this accident of chance gave European sets an advantage, because the slower 50 Hz refresh rate gave the CRT time to scan more detail. However this rate also introduced more flicker, and exacerbated the negative effects of interlace, so sets that use digital technology to double the refresh rate to 100 Hz are now popular.

    Another problem with 50 Hz standards is that motion pictures cannot be easily presented in the typical 24 fps rate used for 35 mm film. These must be accelerated by 4% - with an accompanying slight shift in the pitch of the audio. NTSC sets can display both 24 fps and 25 fps material without speed shift by using a technique called 3:2 pulldown, but at the expense of introducing Telecine Judder.

    Unlike computer monitors, HDTV and some DVDs, analog television systems use interlace, which increases flicker compared to a progressive scan image at the same refresh rate. The amount of extra flicker is largely dependent on the content of the image, and the brightness of the screen. Many newer televisions are flicker-free."

    Last edited: Apr 6, 2008
  16. Apr 6, 2008 #15


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    Electric clocks followed AC electricity by quite a long time.
    Westinghouse famously worked out that if they did regulate the load carefully ( they used to actually speed up/slow down the rate at the end of the day to make sure they sent extactly 24*60*60*60 cycles) the amount of extra electricity used by people buying electric clocks would offset the costs.

    Whether Tesla was thinking this far ahead, or wanted to use existing clock mechanisms in his experiments or just thought that 60hz was a nice fit to mins/secs - I don't know.
  17. Apr 6, 2008 #16
    How about the speeds of a phonograph turntable? Was 60 Hz relied upon for the speeds to be accurate?
  18. Apr 6, 2008 #17
    60 Hz was the standard long, long before there were electric turntables. But, yes, when they were developed, they did depend on the frequency.
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