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Why 220@50hz and 120@60hz?

  1. Nov 22, 2004 #1
    Why 220v@50hz and 120v@60hz?

    Who came up with these and why are they different - especially the frequencies?

    I heard that when Tesla was around, someone wanted the frequency to be @330... why?
  2. jcsd
  3. Nov 23, 2004 #2
    After Tesla won the AC/DC fight with Edison he gained much influence and more or less dictated the 60Hz frequency in the US. I think he had an ulterior motive in that he wanted to transmit power without wires and had calculated the 60Hz frequency was best for that purpose. I have no idea why the European nations choose 50Hz, as it is less efficient to produce and transmit over wire than 60Hz. The best frequency for power transmission is probably moderately higher than 60Hz.

    Consider above opinion not fact.
  4. Nov 23, 2004 #3
    I suspect it was to do with how fast the old generators could spin before they flew apart.

    If you compare the size and mass of a 10 killowatt aircraft generator or induction motor (which run at 400 Hz) with a 10 killowatt 50 or 60 Hz unit, you'll be left wondering why we're not using higher frequencies (the equivalent aircraft units are tiny).

    I suppose the frequency can't be too high for long distance transmission of power (there would be more losses), but I suspect it could easily be a lot higher than 60Hz.
  5. Nov 23, 2004 #4
    from what i understand europe picked 50Hz because it was felt it be easier number to work with due to the metric system as for the voltage, that is what edison picked when he came up with dc
  6. Nov 28, 2004 #5

    That's a horrible reason. :D
  7. Nov 28, 2004 #6


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    I seriously doubt it.
  8. Nov 28, 2004 #7

    Ivan Seeking

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    Here is some information on the evolution of 50 Hz. It seems that a combination of the engine and generators used, the ideal engine speeds, the desired voltage, and the number of poles used in the generators drove the selection of frequency in a complex fashion. I doubt that any simple answer exists.
  9. Nov 28, 2004 #8
    There may be some places in the world that use 20 Hz. The old streetcar used 20 Hz. When they were taken out of service the power plants were sold to some cities in other countries. They were still in use about 20 years ago. I think the reason they used 20 Hz back then is that they used rotary rectifiers. The motor on the streetcar was DC.
  10. Dec 4, 2004 #9
    Up to the '40's the iron laminations of rotors and stators of electric motors and generating equipment were poor quality and hysteresis losses were a major factor. (note how large old electric motors are compared to newer ones). Higher frequencies would have worsened the losses so up 'till then 25 Hz was common in Canada and the US.
    When better steel was used for laminations, north America changed to 60 Hz about 1950, the Europeans decided 50 Hz was the cat's meow.
  11. Dec 13, 2004 #10
    I heard that the European used 50Hz becasue it apparently interefered with you heart less that 60Hz.
  12. Mar 27, 2006 #11
    Reasons for 60Hz

    I heard two different reasons for the US choosing 60Hz. One as mentioned above, the Europeans chose 50Hz because of better calculations with the Metric system. Likewise, the US chose 60Hz to better measure periodic voltage (60 minutes, 60 seconds).

    The other, more 'Urban Legend' reason why the US choose 60Hz was in one of its first applications--The Electric Chair--it was determined that 60Hz was the optimum Frequency to Kill a human. This then became the standard. LIKE I SAID I HEARD THAT RECENTLY FROM AN MIT PHD Professor. Doesn't make that much sense though if you consider that same danger is being carried out to every home.
  13. Mar 28, 2006 #12


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    I once heard that the reason for 60 hertz is that is was the highest frequency you could get without developing standing waves on a trans-continental transmission line.
  14. Mar 28, 2006 #13


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    He's wrong.
    Edison was desperate in his attempts to discredit Westinghouse's AC system and was resorting to all sorts of public relation propaganda to prove how dangerous it was (including the promotion of the electric chair). It was hardly to Westinghouse's (or Tesla, his top engineer that designed the modern 3 phase system) advantage to promote the "deadliness" of his product.
  15. Apr 19, 2006 #14
    Not to dig up a dead thread but I read a biography on tesla 2 years ago and remember reading about the 50hz vs 60hz debate. Tesla intended his generators to be run at 60hz but the french operators (at the first ac generator in europe) didn't want to speed up their machines, or something the like. From that point on every one just followed suit and didn't question, untill now ;-)
  16. Apr 20, 2006 #15
    Which makes me question the 15 kV 16 2/3 Hz railroad power that seems to be adapted as a standard in many European countries. Do they use different generating stations than the regular 50 Hz, or do they do some complicated frequency change somewhere along the line?

    And why 16 2/3 Hz? Something with the old locomotives? I doubt it matters much these days with the thyristor locos.
  17. Apr 21, 2006 #16
  18. Apr 22, 2006 #17


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    When I was in Japan, I learned that east is 50 Hz and west 60Hz.

    Eastern Japan 50 Hz (Tokyo, Kawasaki, Sapporo, Yokohama, and Sendai); Western Japan 60 Hz (Osaka, Kyoto, Kobe, Nagoya, Hiroshima)

    Basically, TEPCO (Tokyo Electric Power Co.) is the main supplier in east, and KEPCO (Kansai Electric Power Co.) is main supplier in west.


    Regarding 220 V @ 50 Hz and 120 V @ 60 Hz, IIRC 220V is line-to-line voltage in a 3 phase system, and 120 V is line-to-neutral. This has to do with 'Y' vs [itex]\Delta[/itex] configuration.

    Several electrified railways used 25 Hz in US.
  19. Apr 22, 2006 #18


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    Wye configuration has 120 volts from each phase to neutral and 208 volts phase to phase.
    Delta configuration has 240 volts phase to phase and the neutral is a center tap on one of the transformers yielding a 120 volt line to neutral on 2 of the legs and the wild leg is something like 160 volts to neutral.
    Standard single phase residential is 240 volts line to line and the center tapped neutral is obviously 120 volts to each line. There is only one transformer secondary winding in residential single phase. It is commonly called 2-phase which is incorrect.
  20. Apr 22, 2006 #19
    I recall a story of early lights hooked up to 25 or so Hz giving people headaches and ill effects because you could actually detect the flicker in the lights, which I guess would be frigging irritating after a while.
  21. Apr 24, 2006 #20


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    Although I don't know much about how the ferquencies wre chosen back in the day, I know that now an important consideration in modern times is an interesting phenomenon known as the "skin effect." This strange occurence makes the current distribution concentrate about 80-85% of the total volume current within the skin depth of the conductor. This depth can be calculated by the simple formula shown in this wikipedia article:


    The reason this becomes a problem is that your effective resistance becomes much larger as you increase the ferquency, since your effective area of your conductor decreases as the skin depth gets smaller. This can become a real problem in high-frequency laboratory applications because ferquencies in the MHz range dirstibute most of the current within the first few dozen nanometers!

    Anyway, the article also has a small table showing the skin depth in a copper conductor at various frequencies, the depth for 60Hz is only 8.5mm. For an extension cord this doesn't lead to any probelms, but what about a power trnasmission line that's 2.5" in diameter? Just food for thought.

    Power transmission lines don't use copper, they use stronger metals such as steel I think. The skin depth for steel at the same frequency can be on the order of 1.5mm, futher exacerbating the problem.
  22. Apr 28, 2006 #21
    Why 220v@50hz and 120v@60hz?


    There are really two different questions in voiced in this:

    1) Why the US (and most of the Americas) uses 60 Hz and Europe (and the rest of the world) uses 50 Hz?
    2) Why does the US uses 110 V (now set at 120 V) and Europe uses 220 V (now set to 230 V)?

    It does seem to be a conglomeration of historical reasons, including state of the art back in 1890’s, which company had a head start, and standardization. Some history:

    George Westinghouse did his original engineering using 133 1/3 Hz. Westinghouse had an steam engine driven alternator set running at 2000 rpm (By 1886 mechanical engineers liked to have steam engines in integral numbers of rpm) and with 8 poles the set produced 8000 cycles per minute or 133 1/3 Hz. This was good for lighting as there was no flicker but it turned out it was too high for motors later developed.

    The earliest experiments (1886 and 1887) used belt driven generators and tended toward high frequencies like 133 1/3 Hz. This suited illumination, which was practically all that alternating current was used for at that time. By 1889 and 1890 direct driven generators were coming on line. They were more robust but with lower rotation speeds they encouraged lower frequencies.

    In the early years of ac there were many frequencies: each engineering team seemed to pick their own. Early frequencies in the US were 133 1/3, 125, 83 1/3, 66 2/3, 60, 50, 40, 30, 25 Hz. When Tesla joined Westinghouse, it was using 133 1/3 Hz. Tesla insisted upon 60 Hz because his ac induction motor was designed for 60 Hz and apparently wouldn’t work at 133 1/3 Hz.

    On the Westinghouse Museum website it says that G. Westinghouse assigned his engineers Stillwell, Shallenberger, Schmid, and Scott to find a good frequency. Practical considerations of connecting alternating generators to reciprocating engines then in use demanded a lower frequency than 133 Hz.
    Before the end of 1892 they chose 2 frequencies: 60 Hz for lighting and 30 Hz where power was to be converted to DC.

    Why did Tesla/ Westinghouse engineering team choose 60 Hz? If it was Tesla that was the driving force, various biographies of Tesla declare different theories ranging from Tesla “thought it was the fundamental frequency of the universe” to “… considered the natural earth had a frequency of 10 Hz and doing experiments with 8 to 20 Hz and 20 to 40 Hz and finally 40 to 100 Hz; he decided that 60 Hz was safe.” It doesn’t seem to have been a desire to do accurate clocks because Henry Warren didn’t patent the synchronized clock until 1916 long after the frequency was chosen. Although Warren was diligent in getting utilities to have tight specs on frequency this didn’t happen until into the 1920’s.

    Back in the early 1890’s Westinghouse was involved in bidding electrical equipment for the Niagara Falls power project. However the Cataract Company (in charge of the Niagara Falls project) had already selected hydraulic turbines running at 250 rpm. So if a 16-pole generator were chosen the frequency would be 33 1/3 Hz and if a 12-pole machine were chosen then the frequency would be 25 Hz. The project consultant proposed an 8-pole generator or 16 2/3 Hz. The compromise was 25 Hz. At the time lower frequencies were easier to handle on transmission lines. Another reason is that the Steel industry liked 25 Hz because of huge slow speed induction rollers, which had a low power factor for 60 Hz and worked better at 25 Hz. Niagara Falls generated 25 Hz way into the 20th century. The website says that the Westinghouse Company later wished it had forced through 30 Hz.

    By 1910 it looked there would be two frequencies in North America, 25Hz for transmission and heavy industry that needed dc or slow moving heavy machinery and 60 Hz for lighting (less flicker) and general use.

    There was an effort by GE to introduce 40 Hz as a compromise between 25 Hz and 60 Hz in the 1890’s but it was too late to overtake the 60 Hz and 25 Hz infrastructures already in place although there were some 40 Hz installations. Even so most installations in the US were done in 60 Hz after Westinghouse and GE cross licensed their patents.

    Development of high-speed turbines instead of slow reciprocating machinery and later developments of the rotary converter that worked well at 60 Hz made it easy to shift everything to 60 Hz. By 1920 most of the problems associated with 60 Hz transmission had been solved so that there was no longer any advantage of transmitting 25 Hz over 60 Hz. That seems to be why the US is 60 Hz.

    Germany took the lead in Europe of developing electrical power (primarily Emil Rathenau of AEG) and AEG seems to have used 50 Hz from day one. In 1891 AEG had demonstrated power delivery over long distances using 50 Hz. I don’t know why AEG chose 50 Hz. Did the penchant for integer rpm help influence AEG for 3000 rpm and 50 Hz as opposed to 3600 rpm and 60 Hz? Did the preference for preferred numbers influence the choice of 50 Hz over 60 Hz? Did Tesla’s influence pull Westinghouse to choose 60 Hz and resultant 3600 rpm over 50 Hz and 3000 rpm? Europe was even more fragmented in the early days than the US. In 1918 in London alone there were 70 electric authorities with 50 different types of systems and 10 different frequencies and 24 different voltages. But by the 1920’s and 1930’s more and more of Europe was changing to or working with 50 Hz.

    As for voltages both Europe and the US seemed to have begun with about 100 to 110 Volts DC because of Edison’s success with replacing gas lights with electric lamps. Although many inventors worked on electric lights, generators and electrical systems, Edison was one of the first and was successful in putting together whole systems not just the pieces. Edison picked 110 VDC because that was the voltage he needed to get enough light out of his bulbs to compete with common gas lamps of the time and yet not blow the filaments in his bulbs too soon.

    The Berlin Electric Works (utility owned by AEG) changed from 110 V to 220 V starting in about 1899 to enlarge the capacity of their distribution system since the city (Berlin) was already wired 2 wires. They were probably changing from dc to ac at the time also. They paid for their customers to change their lighting and motors to 220 V and saved on the cost of copper by avoiding having to add more wiring. This spread throughout Germany and later Europe but didn’t take hold in the US.

    I wonder if the residue from the bitter conflict between Edison and Westinghouse about the safety of AC vs. DC spilled over into not going above 110 volts for residential users even after Edison’s forces conceded the need for AC.

    A lot of this information comes from Thomas Hughes Networks of Power : Electrification in Western Society, 1880-1930 and Benjamin Lamme Technical Story of Frequencies IEEE transactions 37 (1918) 60. Benjamin Lamme was chief engineer for Westinghouse in the early 1900’s.
  23. Aug 1, 2006 #22


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    Thank you Jerry for the best data I can find on the 'net.

    On small thing to add: the key reason the US did not transition to 220 V appears to be that by the time the added capacity played a role, the deployment of industry and consumer goods that assumed 110 V had already progressed so far in the US (but not in Europe) that conversion was too expensive.

    Also, I'm curious about whether AEG decided on 50 Hz to be intentionally incompatible, since AEG immediately went into the business of making consumer products. But I cannot find any evidence at all to back that up, it's just an evil theory.
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