Were any vintage machines run of 50 Hz power in the USA? - Page 2
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  1. #21
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    We build a lot of large pumping systems for use all over the world and to me 50Hz is essentially "diet" power.

    Virtually all motors that are made today are dual rated to save costs for the manufacturers on maintaining separate product lines as all the major brands today are all multinational. So on 50Hz you take a derating where for example a 25Hp @60HZ becomes 20Hp @ 50Hz. Also your pump must get bigger to hit the same flows on 50Hz as it spins slower. It's not uncommon to see on a larger project that 50Hz adds 10's of $1000's on larger systems.

    Typically the total cost adders seem to come in each time a little under the cost of a similar sized VFD it seeks or else we'd just buy 25HP VFD's. So at least for the end user the higher the frequency the less copper needed in the motor and the lower the cost per fixed HP

    I have always wondered however how they came to 50 vs 60Hz and where is the tradeoff? From my perspective higher frequency is always better if 60 was better than 50 why didn't they go 80Hz?

    I wonder if transformer costs or generator costs go up with higher frequency allowing for a lower cost to setup a grid with lower frequency? Does motor efficiency change with frequency?

    Sent from my SM-J737V using Tapatalk

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    At 50 hz the light blink, ie you see the hz, at 60hz you do not, and when it was adopted it was great for clocks...25 and 50 hz gave slow speed motors, and electric motors were replacing steam engines...so the slower the better...why not 70-80hz, would not work easy for clocks and the need was slower motors not faster...so 60hz won, and keep in mind the first voltages were 100, 200, and 400 volts but to get away from big use of copper the voltage has raised 20% over the years... and in the us 25 and 50hz went the way of the dodo bird....Phil

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    Quote Originally Posted by adammil1 View Post
    .................... From my perspective higher frequency is always better if 60 was better than 50 why didn't they go 80Hz?

    I wonder if transformer costs or generator costs go up with higher frequency allowing for a lower cost to setup a grid with lower frequency? Does motor efficiency change with frequency?

    Sent from my SM-J737V using Tapatalk
    Iron losses go up with frequency, for starters. Then transmission lines have inductance and would have more drop of voltage per km with a higher frequency. They have capacitance also, which adds reactive current with higher frequency.

    Feed- through on a switch is more with higher frequency. So is capacitive coupling between energized and non-energized conductors.

    These things generally go as the ratio of frequencies, so 60 Hz is 20% worse than 50 Hz, but also takes 20% less iron in a transformer.

    It's a tradeoff, and if you know your costs, you can make a tradeoff intelligently.

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    Don't forget skin effect. A high frequency conductor only conducts along it's very outer 'skin'... the bulk of the mass inside of it remains totally inert.

    This is why transmission lines have a ~9mm thick aluminum braid over a steel core. Also why bussbar in switchgear is flat.

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    The depth of the "skin effect" depends on the frequency and the resistivity of the material. For a perfect conductor, it would be infinitely thin. The more resistance, the deeper the current flows.

    It is surprisingly shallow for 60 Hz. And would be half as thick for 120 Hz.

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    At 60hz the skin effect would be close to 0, I have never seen any calks for cap. of conductors that even factored in 60 hz...Phil

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    Quote Originally Posted by Phil in Montana View Post
    At 60hz the skin effect would be close to 0, I have never seen any calks for cap. of conductors that even factored in 60 hz...Phil
    It's factored right into the ampacity tables in the code. Look at 310.16. Compare the cross section of wires in the 250-2000kcmil range relative to their ampacities.

    255A for a 250kcmil conductor at 75*C... only 665A for a 2000kcmil conductor of the same temperature rating.

    255/250 = 1.02A/kcmil
    665/2000 = 0.3325A/kcmil

    The effect becomes even more pronounced if you use Chapter 9, Table 8 to convert wire gauge to cmil area.

    8AWG = 16.51kcmil
    8AWG @ 75*C = 50A ampacity

    50/16.51= 3A/kcmil.

    This is (one of the reasons) why big services and feeders are always paralelled.

    Pulling anything over 600-750kcmil is just idiocy unless there's no other way to do it.

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    I did not read all of the posts here. I recalled reading a book about the history of the Philadelphia Electric Company which mentioned that they supplied 25 hz power for the subway system. I just Google that and apparently most subway systems still run on 25 hz.
    I know that Philadelphia also supplied 2 phase power in the past.

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    Sparky, I dont agree, the lower amp/cm ratio is do to the radiation of heat not skin affect. and the why of parallel wires is the king kong effect , your not man enough to bend the bigger stuff.as a electrician you know that..Phil

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    Quote Originally Posted by Harold Mulder View Post
    When I was in my youth in Niagara on the lake we had an old fridge that the parents got with the house when they bought it in around 1958.
    I remember that on the back it stated the motor had been converted from 25hz to 60hz before they bought the house. Not sure the age of the fridge
    but my guess is that we had 25Hz into the early 50's here.

    Harold
    Dad, Commanding Fort Ethan Allen, VT at the time, whilst turning it over from US Army to the USAF, got us a family tour "plus plus" at a Niagara Falls generator hall 1950.

    ISTR that one of the high points was that not all the turbines were the same, and that 50 Hz was going to the Canadian side.

    Could have been we were there during a gradual conversion period?

    Only age five at the time, I only remember it because we stayed that night in a place in Canada that had Fluorescent lights. The flicker was rudely annoying, and Dad had to explain why that was and he related it back to the generator.


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