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Why 220V/50Hz or 110V/60Hz?

  1. Jun 8, 2015 #1
    Why not some other configurations, like 150V/100Hz or 500V/500Hz?

    I'm referring to the mains electricity.
     
  2. jcsd
  3. Jun 8, 2015 #2

    Hesch

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    Mains electricity requires big transformers, therefore laminated iron is chosen as core ( low price ).

    Several calculations have been done to find the lowest all-over-price for a transformer, considering:

    - Highest voltage per turn.
    - Iron losses due to eddy currents and hysteresis losses in iron.
    - Copper prices and iron prices.
    - Amount of iron/copper required to build a transformer.

    These calculations have (years ago) come up with an optimal frequency ≈ 55 Hz. But maybe ( as copper prices have increased ) the optimal frequency has now become 65 Hz? But it will be very expensive to change the frequency now.
     
    Last edited: Jun 8, 2015
  4. Jun 8, 2015 #3
    There ARE other standards... Like 440V/60Hz 380V/50Hz. Whats stopping a uniform code is just human laziness and rigidity.
     
  5. Jun 8, 2015 #4

    Hesch

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    I think the frequency is in question here, not the voltage.

    50Hz is a european standard, 60Hz is american.
     
  6. Jun 8, 2015 #5
    Oh ok. That has already been done to death on the forum lol
     
  7. Jun 8, 2015 #6

    psparky

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    To sort of follow up on this conversation, it's been brought to my attention that a 460/3/60 hvac unit can run just fine on a 380/3/50 circuit. Perhaps the manufacturer built a custom unit.

    The specs for the original unit are a minimum circuit ampacity of 21 amps with a 25 amp circuit breaker. This is for a 460/3/60 unit run on a 460/3/60 circuit.

    With the new 380 unit, I am going to make the same horsepower, but I am going to draw more amps because of lower voltage. I can see how a ratio from 460 to 380 could figure out your new higher amps....but does the 60 to 50 hz make a difference? I have a feeling it does because your impedance is certainly going to be different!

    Any thoughts on this? Yes, the manufacturer is going to give me a number on this, but I would rather understand the math behind it.
     
  8. Jun 8, 2015 #7

    SteamKing

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    Also the fact that ripping out and replacing the electrical infrastructure of one continent or the other would not be quick, easy, or cheap.

    How long would you be willing to sit in the dark just so that all electricity is the same standard voltage and frequency?
     
  9. Jun 8, 2015 #8

    Hesch

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    @psparky: A transformer is a very robust component that can "run just fine" with other (lower) voltages and frequecies. But it's not optimal any longer, regarding wear in the transformer.

    Mains transformers are expensive, thus you want such a transformer to function the next 20 years. When you overload the transformer, it will not be broken, it will just increase its life-time-consumption (free translation from danish) so that it can use 5 hours/hour of its lifetime. The transformer will be worn by high temperatures (insulation will be worn), and the life-time-consumption will increase drastically even by a few deg C above ratings.
    When you lower the voltage and the current goes up, the ironcore will get colder, but the coils will get warmer. The transformer will get skew as to temperature, and its life will not last 20 years. ( It will short circuit within 15 years. )
    Well, you have a transformer formula (sinusoidal current/voltage):
    Veff = 4,44 * f * N * A * B. (f=frequency, N=number of turns, A=cross section area of magnetic circuit, B=magnetic induction).
    So changing f, you must change N*A*B.

    Increasing N → thinner wire → increased copper losses
    Increasing A is not a relevant option.
    Increasing B → higher iron losses
    but
    decreasing f → lower iron losses

    So the answer to your question is: yes, some good and some bad differences.
    It's a hard job to optimize a transformer (a lot of calculations), so you use a computerprogram combined with a "cut and try" process to optimize it.
     
    Last edited: Jun 8, 2015
  10. Jun 8, 2015 #9

    jim hardy

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    It's volts per hertz that matters to the transformer and motor cores.
    460 X50/60 =383 , so the voltage reduction to 380 looks about right because it'll make flux be the same.

    hmmmmm but it seems to me the motors are going to run slower at 50 hz that at 60 unless they have vfd's.

    fan affinity laws say fan power is cube of speed so the fans will draw a lot less power

    the positive displacement compressor is the biggest motor, i think it'd be linear..

    Is the unit rated same tonnage at 50hz as at 60 ? Or 5/6 (.833) as much ?
     
  11. Jun 8, 2015 #10

    anorlunda

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    400 hertz is common in aircraft systems because it weighs less.

    Years ago the Russians studied the question of optimum power grid frequency if no history existed. They considered all components and effects, not just transformers. Their result was 100 hertz. The reaction of the world was "Who cares?", because of the reasons Steamking cited.

    Many years ago, I was involved with the conversion of Mexico from 50 to 60 hertz. It was messy, complicated and expensive. Nobody would do that unless there were powerful reasons.

    See:
    http://en.m.wikipedia.org/wiki/Utility_frequency
     
  12. Jun 8, 2015 #11

    Hesch

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    Optimum power grid frequency regarding what?

    In America and Europe we are regarding economy/costs.

    I don't think you can compare american/european economy with russian economy.
     
  13. Jun 8, 2015 #12

    anorlunda

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    Optimum regarding costs.

    You're porbably right about Russian versus western costs, but my guess is the the, "Who cares?" Is universal.
     
  14. Jun 8, 2015 #13

    Hesch

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    Don't be so sure about that:

    A year ago the EU-countries agreed that all cars must have their rear lights switched off in daylight ? ? ?

    Well, we must start one place to save energy, starting with the 6W bulb. :smile:
     
  15. Jun 9, 2015 #14

    psparky

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    Not sure there is a transformer involved in this situation. But I haven't seen the final spec sheet.
     
    Last edited: Jun 9, 2015
  16. Jun 9, 2015 #15

    psparky

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    Actually, it was going to be a 7 ton unit, but they changed it to a 10 ton........the mechanical guy said the 10 ton was "de-rated".

    2 compressors running at 7.8 amps (RLA) a piece and one fan running at 4.2 amps (FLA).
    That is the specs for the unit when it is hooked up to a 460/3/60 source.
    With a voltage source of 380/3/50 these gonna change obviously.

    Hopefully the rep gets back soon. I hate to "guess" a 30 amp breaker with 10 guage wire, but it prob is a decent guess.

    Edit:
    Oh wait, I see what your saying Jim Hardy. (there are NO vfd's) Fans are turning 5/6 the speed....and 380 just happens to be 5/6 of 460. So should theoretically use same amps.....with the original MOCP of 25 should be correct.

    Should be correct.....lol....

    You'll get the cubed effect the 4.6 amp fan which wont matter a ton since it will actually lower a bit....and the compressors should work on the 5/6 ratio.
     
    Last edited: Jun 9, 2015
  17. Jun 9, 2015 #16

    jim hardy

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    That'd be interesting trivia to know, why they "derated " it and what was the thought process..

    If it's because the compressor moves only 83% as much refrigerant at 50 hz, then the unit ought to run very well for it'll have more than enough area in its heat exchangers.
     
  18. Jun 9, 2015 #17

    psparky

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    Thanks Jim. Ya, that is interesting. I think your guess about moving less refrigerant sounds reasonable.

    I'll report back when I more info.

    Here's where things get fun. I need to issue this for construction. But I am waiting on a rep.
    Do I delay the job?.....or do I issue job with our relative decent guess?

    The answer is neither. I will harass the rep until she harasses her engineer enough to get the exact answer.
     
  19. Jun 9, 2015 #18

    psparky

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    Just talked to my mechanical guy....that is exactly why they had to use a 10 ton unit instead of a 7 ton.

    Also, the fan doesn't quite make the 4000 CFM mark they are looking for so they are going to change the pulleys a bit to make it more like 60 hz.....I suppose that will put the fan amps closer to there original spec since the 50 Hz motor will pull more amps to maintain its same speed while spinning the fan faster via pulley ratios.

    I guess we really can't buy 50 Hz hvac units in the states....or if you can they aren't very good.
    Mechanical guy says its always tricky hooking up quality units to 50 hz sources, but factories make it work on this 5/6 ratio.

    Perhaps that's why the 50 Hz countries use the 400/380 voltage instead of our 480/460 voltage. Makes sense....keeps the 5/6 ratio.
     
    Last edited: Jun 9, 2015
  20. Jun 9, 2015 #19

    jim hardy

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    As usual your common sense shines through

    hmmm
    to provide same blower RPM, the fan motor at 3000 rpm (minus slip) with a (let's just say) 6 inch pulley
    will have to deliver 6/5 of the torque that it would at 3600 rpm and a 5 inch pulley,
    meaning it'll draw somewhat higher amps, because it's a little higher up its torque vs speed curve.
    I'd be darn sure to measure blower motor amps, compare to nameplate as part of startup acceptance tests.
    Compressor should be fine i'd think
    but some measurements will arm you for future conversations.

    If everything turns out fine you don't have to admit you were ever concerned, brush it off as "just being thorough".



    old jim
     
  21. Jun 9, 2015 #20

    Baluncore

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    European harmonisation to a specified 230V 50Hz has now replaced the 220V, 230V and 240V AC standards. This does not mean that any national standard voltages have changed, it just means that they call it 230V with a +/– 10% tolerance. That tolerance includes all supplies in the range from 207V to 253V AC.

    A 230V single phase voltage implies a 400V three phase voltage and a 115V half voltage.
    The specification of 230VAC with either 50Hz or 60Hz is gradually becoming an international standard.
     
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