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  1. #21
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    Quote Originally Posted by TDegenhart View Post
    The beauty of AC is that as the system demand increased, it was only necessary to increase the system voltage to increase the system capacity.

    Tom
    Yes indeed... although that "just" did involve some expensive transformers, so one has to remember that the generating equipment was even more expensive.... so transformers were not so bad, and only needed to be at each end of the line. There might have been some issues of insulators as well, of course.
    Y

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    Quote Originally Posted by jim rozen View Post
    This
    cannot be changed because physics is a harsh mistress.
    TANSTAAFL

    The efficiency of transformers does not increase with frequency. The power to weight and bulk ratio does improve. Typically 60 CPS transformers use 12 mil laminations. 400 CPS ones use 4 mil. Rolling the silicon steel out to .004" thickness distorts the grain structure and the magnetic qualities suffer, but it is still better than the higher eddy current losses of the thicker material. When I made a transformer for the output of a bus alternator ranging from 125 CPS to 625 CPS, I asked for 4 mil, assuming it would be needed for the higher frequency. Lou Rothlisberger at Electrocore suggested I try 12 mil first. When I got good results, I finally realized what he was talking about. Using a core and number of turns for 125 CPS to work at 15,000 Gauss, at 625 CPS the flux density would be 1/5 that, 3,000 Gauss, and the core would be hardly working. It did have some loss in output at the high end, apparently mostly from leakage reactance but it was acceptable. As an example of how sensitive these things can be, I had to twist the leads from the alternator to reduce their inductance. Spacing them apart caused a definite loss in output at the high end.

    The reason for 400 cycle equipment in airplanes is the voltage per turn on a core is linear with frequency. A 400 cycle transformer only needs 1/7 the number of turns on the same sized core. In practice designers take the gain from both sides, reducing both the core size and number of turns.

    BTW, it is Cycles Per Second. Expletive this Hertz nonsense.

    Bill

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    Quote Originally Posted by 9100 View Post
    TANSTAAFL

    The efficiency of transformers does not increase with frequency. The power to weight and bulk ratio does improve. Typically 60 CPS transformers use 12 mil laminations. 400 CPS ones use 4 mil. Rolling the silicon steel out to .004" thickness distorts the grain structure and the magnetic qualities suffer, (That could have been corrected by a hydrogen anneal) but it is still better than the higher eddy current losses of the thicker material. When I made a transformer for the output of a bus alternator ranging from 125 CPS to 625 CPS, I asked for 4 mil, assuming it would be needed for the higher frequency. Lou Rothlisberger at Electrocore suggested I try 12 mil first. When I got good results, I finally realized what he was talking about. Using a core and number of turns for 125 CPS to work at 15,000 Gauss, at 625 CPS the flux density would be 1/5 that, 3,000 Gauss, and the core would be hardly working. It did have some loss in output at the high end, apparently mostly from leakage reactance but it was acceptable. As an example of how sensitive these things can be, I had to twist the leads from the alternator to reduce their inductance. Spacing them apart caused a definite loss in output at the high end.

    The reason for 400 cycle equipment in airplanes is the voltage per turn on a core is linear with frequency. A 400 cycle transformer only needs 1/7 the number of turns on the same sized core. In practice designers take the gain from both sides, reducing both the core size and number of turns.

    BTW, it is Cycles Per Second. Expletive this Hertz nonsense.

    Bill
    Tom 12characters

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    These were tape wound cores that were annealed after winding, the tape, not the copper coils. They use nitrogen and they get an overnight heat up and cool down. The cooldown must be no more than so many degrees per hour. We looked at vacuum annealing to eliminate the cost of the liquid nitrogen, just for storage and converted to gas for use. Baking in a vacuum was fine but getting the heat out was a problem. Remember that we are talking about hundreds of pounds in a run, a lot of stored BTUs. I had little to do with evaluation after annealing but I do know that they remain grain oriented. One of the selling points of tape wound cores is that the grain is always parallel to the magnetic lines whereas in EI laminations, part of them have to be wrong.

    I don't know all the reasons for the degradation in the thinner material but I do know that you wouldn't want to use 4 mil tape in a 60 cycle transformer.

    Bill

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    Reason not to use 4 mil is the fixed thickness of insulation.

    For 4$ a pound you can buy 12mil tape wound cores that have about 1 watt per kilogram core losses at 1.7T at 60hz.

    I doubt you could push a 400hz, 4 mil core that hard, but 1.3 T is ok

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    Quote Originally Posted by johansen View Post
    Reason not to use 4 mil is the fixed thickness of insulation.

    For 4$ a pound you can buy 12mil tape wound cores that have about 1 watt per kilogram core losses at 1.7T at 60hz.

    I doubt you could push a 400hz, 4 mil core that hard, but 1.3 T is ok
    Are you referring to the insulation on the surface of the tape and the ratio of magnetic material vs insulation in the cross section? That would make sense since the flux has to jump the gap between layers.

    That would also influence the flux transfer across a cut core. The thicker material would be less sensitive to misalignment. I know that no matter what you do, you can't get a cut core up to the performance of an uncut one. In the example I cited, it was a hexafilar #8 square winding and I am not about to try to wind one on a solid core.

    Bill

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    Quote Originally Posted by Froneck View Post
    I read what Tesla claimed. Something must have been correct since all power generation in all countries is 50 or 60Hz. I haven't heard of anyone planning or even arguing it should be increased. I know aircraft us 400 Hz, read sometime ago why but can't remember!
    400HZ is easier to rectify into DC. Filter components are smaller which means less weight and less space.

    Bob
    WB8NQW

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    Quote Originally Posted by TDegenhart View Post
    Weight.

    Tom
    Yes. The same impedance is obtained with a smaller inductance, so the core can be smaller. Works for motors, transformers, any electromagnetic thing that needs an iron core, or even air core coils that need to be smaller and lighter. It does not change the wire size, which may actually get larger overall, but it really takes care of weight and bulk of the overall part. At even higher frequencies, a 2500W transformer can be as small as about 3.5" x 2.5" x 1 1/4", and weigh very little.

    At 400Hz, things are bigger, but practical laminations and core types are usable. Frequency effects are not too bad, and you still get a weight savings that is good enough to give a significant advantage.

    I have seen a generator rated at 250kW that was 5 phase at 1000Hz (intended for rectification and the final output was from an inverter). One person could pick it up without much strain. That used a different core material for efficiency, but still could have used transformer steel if necessary.

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    Quote Originally Posted by Froneck View Post
    According to Tesla 60cps was the frequency of the Earth, changing to 60cps made the transformers efficient and the rest is history! From what I have also read that measured frequency of the Earth is 57Hz using modern measuring methods
    The frequency of the Earth?
    I never heard of dat, so please tell me, sumbody!
    Regards, fusker

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    OT, but when did that bother us, this thread reminded me that St. Louis was once on 25 cycle power. The original Niagara Falls generators, designed by Nicola Tesla, were 25 cycle and the ones on the Keokuk IA dam were a spinoff from them. I came across this-

    Pardon Our Interruption

    A quote from this article-

    The idea for the Keokuk site came from a young lieutenant named Robert E. Lee, who surveyed the land for the U.S. War Department in 1836. He suggested that the great power he witnessed in this turbulent section of the Mississippi River, known as the Des Moines Rapids, could be harnessed in some fashion.

    When I worked on a project for Wallace Pencil in 1977, they still had some 25 cycle equipment.

    I can't find anything about it, but the area due west of the arch was on DC in 1950. People had to use motor generator converters to run AC appliances.

    Bill

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    Bill, regarding my comment on the insulation thickness, i'm referring to the insulation coating(s) on the surface of the strip. not sure what they do now days but for a .004mil thick strip of steel i would hardly expect a core made from it to be more than 80%. so for a steel that saturates at 1.9T, you're going to get a core that saturates at 1.5T.

    cutting the core, acid etching the cut surface and then polishing it, influences permeability but doesn't influence the saturation flux density.

    At even higher frequencies, a 2500W transformer can be as small as about 3.5" x 2.5" x 1 1/4", and weigh very little.
    the transformer in a flatpack 48v, 3000 watt power supply is about 2 inches by 1.5 inches by 1.1 inches, whole unit is >95% efficiency.
    would be hard to beat that with a 50kg transformer.

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    Quote Originally Posted by fusker View Post
    The frequency of the Earth?
    I never heard of dat, so please tell me, sumbody!
    Regards, fusker
    A while ago I became interested in Tesla, read all I could find. Still have some of the books and a Video. Supposedly Tesla considered the Earths frequency to be 60cps, why the Earth has a frequency I don't know but it was mentioned a few times as well as the supposed frequency currently measured is 57cps. Been a while ago so I don't remember too many details. On the other hand I've read various stories of the same situation about Tesla that were not the same in each of the writings. Not sure which is correct. The information Bill posted was rather interesting, I never knew the Niagara Generators by Tesla was 25cps.
    Loin sumptin ebrie doy!

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    Quote Originally Posted by Froneck View Post
    A while ago I became interested in Tesla, read all I could find. Still have some of the books and a Video. Supposedly Tesla considered the Earths frequency to be 60cps, why the Earth has a frequency I don't know but it was mentioned a few times a well as the supposed frequency currently measured is 57cps. Been a while ago so I don't remember too many details. On the other hand I've read various stories of the same situation about Tesla that were not the same in each of the writings. Not sure which is correct. The information Bill posted was rather interesting, I never knew the Niagara Generators by Tesla was 25cps.
    Loin sumptin ebrie doy!
    I contend that both geniuses and the insane have visions, hallucinations, whatever you chose to call them. The difference is the ability to sort them out and respond to the useful ones. By his own admission, Tesla was on the edge. He suffered from obsessive compulsive problems, had visions he couldn't control. In the case of radio propagation and transmission of wireless power, he was just plain wrong.

    Re 25 cycle power from Niagara, circa 1953 some of my friends visited Buffalo, NY and said they could see incandescent lights flicker.

    Bill

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    Quote Originally Posted by johansen View Post
    Bill, regarding my comment on the insulation thickness, i'm referring to the insulation coating(s) on the surface of the strip. not sure what they do now days but for a .004mil thick strip of steel i would hardly expect a core made from it to be more than 80%. so for a steel that saturates at 1.9T, you're going to get a core that saturates at 1.5T.

    cutting the core, acid etching the cut surface and then polishing it, influences permeability but doesn't influence the saturation flux density.



    the transformer in a flatpack 48v, 3000 watt power supply is about 2 inches by 1.5 inches by 1.1 inches, whole unit is >95% efficiency.
    would be hard to beat that with a 50kg transformer.
    That is what I thought you meant about insulation.

    Cutting a core doesn't change the saturation point but you have to work harder to get there. Re etching, I tested a choke core run at 15,000 CPS. The competitor apparently didn't etch theirs and the temperature rise was markedly higher.

    This is hearsay, but I have been told that the Space Station runs on 25,000 cycle power. That seems past the point of diminishing returns since you can only wind a heavy wire into so tight a winding and the noise coupling would be serious. Back in the day, I had occasion to run 60 cycle equipment at 400 cycles and the noise issue was much worse.

    Bill

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    Quote Originally Posted by 9100 View Post
    I contend that both geniuses and the insane have visions, hallucinations, whatever you chose to call them. The difference is the ability to sort them out and respond to the useful ones. By his own admission, Tesla was on the edge.
    Bill
    It seems there is after all something that could be called 'Earth resonance' (google Schumann resonance) which is triggered by lightning and has very low frequency. AFAIU its something to do with the volume of our planet, considered as a hollow space, acting as an electro-magnetic resonator. The frequencies are much lower than 60 cycles however and the phenomenon has nothing to do with neither 50/60 CPS or the great Tesla.

    Yes, some of us learn of new things every day although we don't understand.
    fusker

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    Quote Originally Posted by 9100 View Post
    ......

    This is hearsay, but I have been told that the Space Station runs on 25,000 cycle power. That seems past the point of diminishing returns since you can only wind a heavy wire into so tight a winding and the noise coupling would be serious. Back in the day, I had occasion to run 60 cycle equipment at 400 cycles and the noise issue was much worse.

    Bill
    I knew a guy who was working on that, and it was true. I assume they ended up with it, I know that was the plan. We had some products that could have been used for producing 25 kHz at fairly high power for testing purposes, and we had some discussions about it.

    It's not so off-the-wall. The weight saving is huge, and the problems are likely not as bad as it seems.

    You do not use "heavy wire" Any wire is likely to be a form of Litz wire for significant current at that frequency, or at least a multi-strand wire. That takes care if the flexibility issue.

    Noise is easier to couple, yes, but also easier to filter out. Noise coupling is also easier to shield, both mag field and electric field.

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    Quote Originally Posted by fusker View Post
    It seems there is after all something that could be called 'Earth resonance' (google Schumann resonance) which is triggered by lightning and has very low frequency. AFAIU its something to do with the volume of our planet, considered as a hollow space, acting as an electro-magnetic resonator. The frequencies are much lower than 60 cycles however and the phenomenon has nothing to do with neither 50/60 CPS or the great Tesla.

    Yes, some of us learn of new things every day although we don't understand.
    fusker
    I looked at Schumann resonance. Our brainwaves are changing the resonant frequency of the earth's electromagnetic field???? Apparently some people take it seriously.

    Bill

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    Quote Originally Posted by 9100 View Post
    ...Our brainwaves are changing the resonant frequency of the earth's electromagnetic field???? Bill
    Not *mine*. The tinfoil in the hat keeps that from happening.....

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    The EU / global 50 Hz-type 3-phase grid with 220V household power needs much smaller wires in houses and permits easy, cheap, and fairly common 3-phase power wherever users want it.
    3-phase mostly has little/no structural costs to deliver to any consumer who wants it.

    Depending, eu, 3-phase may have zero installation costs (modern) to very high costs (antique old city centers and protected buildings and no infra).

    Common household power on household AC, not 3-phase, is 3-4 kW peak per appliance upto 8 kW, for say saunas, spas, etc.
    Amps are usually not commented on or used, just total power in kW.
    220V x 32 amps = 7 kW.
    32 amps is typical max household fuse, bigger ones exist.
    2 wires + gnd.
    Receptacles are not keyed.

    The EU 2-phase AC is much simpler than the US system.
    Less wires (US has 3+gnd, no), not keyed, much less copper and cost, half the wire thickness.

    And dual igbts mean the system is very safe.
    I have shorted the main power by hand, tripping the igbts.
    Nothing happens.
    Not dangerous, no burns, hurts quite a bit.

    Re: VFD, as in tech.
    My Bp-M 3-phase motor circa 1940 was the best possible product of it´s time, extremely expensive.
    18 kg mass, 0.5 Hp sustained output, essentially forever.

    My current 2.5 kW AC servo motor == 10 kg mass, 19 mm shaft, 10 Nm cont, 30 Nm peak, 220V AC (50 Hz).
    The modern ac motor is == 14x better.

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    Quote Originally Posted by jim rozen View Post
    Not *mine*. The tinfoil in the hat keeps that from happening.....
    Yes but are you using real tinfoil or Reynolds Wrap, which is actually aluminum. The different position in the electromotive series changes the galvanic action between it and the salt in your perspiration and your ear rings.

    Bill


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