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just call it 2 phase

Discussion in 'Electrical Engineering' started by [email protected], Feb 18, 2009.

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  1. Guest

    |
    | wrote:
    |>
    |> |
    |> | wrote:
    |> |>
    |> |>
    |> |> | The arcing commutator would generate so much hash that all you would
    |> |> | get would be a loud buzz. Any time the brush loses contact with the
    |> |> | armature, it arcs.
    |> |>
    |> |> And a filter that can remove 60 Hz (or whatever slow rate was in use back in
    |> |> Edisn's day) could not clean up some modulated noise band at higher freqs?
    |> |
    |> |
    |> | Did you even read what you posted? That is one of your most pathetic
    |> | attempts at trolling, to date.
    |>
    |> Do you even understand filters at all?
    |
    |
    | Sure, from line frequency up to 11 GHZ. Ever work with Sallen-Key?
    | Butterworth? How about FIR filters, and using them with DSP? How about
    | UHF diplexers that handle over 200 KW? A filter can only do so much
    | with the input, or we would still be using TRF radios. IOW, you can't
    | make a silk purse out of a sow's ear, no matter how much you whine, or
    | how many hissy fits you throw.

    Very good. You must have done some Googling to find all those terms.


    | The only 'filter' that would work with your ridiculous pulsing DC
    | would be a battery bank or a band of huge electrolytics. The battery
    | would be a better choice, because the electrolytics would heat up quite
    | a bit from all the AC flowing through them.

    They do make filters for smoothing out the ripple that comes from converting
    AC to DC. Ever tried one of those? Most of them are low pass. Raise the
    frequency and the filtering is more effective.


    | Those arching brushes would fail every EMI/RFI standard. Do you
    | understand that? Or to make it even simpler for you, it would wipe out
    | all radio & TV OTA signals for quite a distance. If it was a large
    | power plant, it could be a mile or more each side of the HV distribution
    | lines.

    I never said that arcing brushes would pass EMI/RFI standards. The subject
    was on the power wiring. A low pass filter would block the higher frequencies
    on that path. What you do on the antenna connection is anothr matter.
     
  2. Guest

    |
    | wrote:
    |>
    |> |
    |> | wrote:
    |> |>
    |> |>
    |> |> | A lot of transformerless tube radios were sold as AC/DC, and wouldn't
    |> |> | have worked if it was a Phil claims. You just had to make sure the
    |> |> | power plug was inserted the right way, or you got no B+ for the tubes.
    |> |>
    |> |> And these were plugged into Edison's DC system?
    |> |
    |> |
    |> | No. They were plugged into the cigarette lighter of the flying
    |> | saucers at Area 51. If you are going to continue to post nonsense, I
    |> | might as well, too. :(
    |>
    |> I asked a question. Obviously you never provide useful answers.
    |
    |
    | You never post any useful questions. You just post crap, or try to
    | play troll, but you aren't capable of even doing that properly. WTH
    | would they have built AC/DC radios if they couldn't be operated on
    | Edison's DC generator designs? You can't be that stupid? Or can you?

    Questions are not something that has utility, except for people that want to
    know the answers. You do not need to perceive any utility in questions that
    I or anyone else asks. The utility of a questions does depend on the answers
    is gets.

    AC/DC radios could be built to operate on AC or batteries. You cannot assume
    ever AC/DC radio ever built was intended to operate on the kind of DC system
    Edison ran. It might be that they didn't engage any filtering at all for DC.

    If you had simply answered the question, the conversation would move forward.
    Instead, you clearly have the intent to always derail conversations. Should
    I assume malice on your part? Or maybe just incompetence in reading English?
     
  3. Don Kelly

    Don Kelly Guest

    You are right
    However, in most areas, these were not supplied from DC. I fear that
    the main purpose of these sets (with filaments in series,etc) was not to
    make them useful for both AC and DC service ( advertising was a side
    issue at the time that they were popular -40's to early 50's -they came
    in to being long after most systems were AC) but to eliminate the cost
    and weight of transformers as you indicate. Cheap sets- with reversible
    plugs and no separate chassis grounding- did their share in reducing the
    gene pool (smashed case, put it in the garage or shop- good case, perch
    it on the bathtub).
     
  4. James Sweet

    James Sweet Guest


    Sure that was the whole reason they existed, the "all-american five"
    tube lineup as they were commonly called, transformerless series string
    set was a masterpiece of cost reduction. The fact that they could be
    operated on either AC or DC current was simply a useful side effect of
    that which was marketed as a feature. Nevertheless, it was a side effect
    that some people did make use of.
     
  5. Don Kelly

    Don Kelly Guest




    You are throwing up a problem that didn't exist because efforts to cure
    other problems, which were far more apparent to the operators at the
    time, incidentally took care of this. For a large DC generator, there
    would be serious performance problems with arcing (not arching) brushes-
    particularly under load. In extreme cases, the whole commutator could be
    involved- not good.
    First of all, brush resistance and width are designed so that current
    reversal (which occurs only in the coils under commutation) and is
    completed before the shorting of the coils in which the current was
    reversing was completed. In addition, at the time that this switching
    takes place the voltage induced in the shorted coil is near zero- the
    combination means no arcing. However as load changes the "neutral axis"
    of the machine shifts which could lead to arcing. To take care of this,
    the brushes of early machines could be moved to a position where arcing
    ceased. In later machines, interpoles were used - which added a load
    dependent flux in the coils under the brushes to counter this (armature
    reaction) effect. These replaced manual compensation about 1915-25-
    prior to mains powered radios.
    Where you get arcing and interference is where you have poorly
    maintained commutators and brushes, or, for cost savings, no interpole
    compensation or brush adjustment compensation. Where do you get this?
    Mainly in small and cheap "universal" (DC series) motors which can
    produce a lot of hash (worse on AC).

    The larger machines, where it was important to provide compensation
    would not have failed the EMI/RFI standards if they had existed at the
    time.

    N.B. I have run multiple unfiltered 5-10HP DC motors and generators in
    labs in a building (without any problems with radio or near by labs
    depending on RF and electronics). If any sparking (as opposed to
    arcing) occurred, the commutator was cleaned and the brushes checked or
    replaced. I have been in plants where much larger DC generators are used
    without any problems with RF. On the other hand, I have also run into
    problems with a simple small 12V DC motor completely messing up radio
    control (incidentally, the motor was fed from an automotive battery).

    The "pulsing DC" (and you are right about this being ridiculous) is
    something that did not occur except possibly in machines designed on the
    basis of "build your own DC motor" in children's "explore physics" books.
     
  6. Don Kelly

    Don Kelly Guest

    You could do these things but, in practice, it would be a rather stupid
    step backwards (and somehow involving changes from AC to DC, back to AC
    etc, ad nauseum. Inefficient and bloody expensive.

    For distribution, service, utilization, and different DC voltages, there
    is no comparison, AC wins hands down. With regard to switching, again AC
    wins. For transmission- it is a balance between line and terminal costs
    (point to point systems, not grids) or an asynchronous connection is
    needed- then HVDC has advantages. These factors have been known for
    roughly 80 years or so. As for generation. DC is severely limited- so
    what do we do- generate AC (simpler, cheaper and more efficient) step it
    up or down with simple transformers and then use it in loads that
    generally don't care whether it is AC or DC or can be handled by an
    induction motor in a more efficient and far less complex machine than a
    DC machine.

    So where to use DC? In those places where it provides a cost or
    technical advantage or a specific need for DC (long distance HV
    transmission, long cable systems, asynchronous links between grids,
    aluminum pot lines, electronic power supplies, etc.)
    However, for voltage level changing, switching, and most utilization,
    AC wins. That is a lesson that was learned over 100 years ago and
    modern electronics hasn't changed the situation. Wishful thinking to
    the contrary.
     
  7. One of the largest universal motors must be the traction motors that an
    E-Lok (electric locomotive) has. It's 4 motors of 1 MW each, series,
    supplied with 700 V max, ac, 16 2/3 Hz. Newer technolgy allows them to be
    supplied with 50 Hz. Cetenary is 15 kV 16 2/3 Hz (old lines) and 25 kV, 50
    Hz (newer lines). The AC motors have special construction to avoid arcing
    etc., which under these conditions would be destructive.
    Excitation for a 300 MW, 21 kV, 10 kA, alternator, is 220 V, 1000 A, DC. The
    rings that supply the DC to the alternator, are big as bricks, and usually,
    there's another shunt DC generator, on the same shaft, to excite the
    excitation (shunt DC) generator, and usually, there's also a tacho, too.
     
  8. James Sweet

    James Sweet Guest


    You know, you could just filter him like I did, having done that, I
    don't see his posts, but I still see the useless crap you post in
    response to every one of them.

    I'm starting to see why usenet is dying in favor of moderated discussion
    groups, I just wish the latter were more centralized and had a clean
    standardized interface.
     

  9. Moderated forums are for pussies.
     

  10. Hear! Hear!
     
  11. krw

    krw Guest

    Seconding your own post, DimBulb?
     
  12. Don Kelly

    Don Kelly Guest

    I built one of these a bit over a half century ago- worked well. The
    next was a Heathkit unit that worked better (and the "paint by numbers"
    instructions were such that the "rats nest" situation didn't occur -if
    they were followed).
     
  13. krw

    krw Guest

    I built one of them, then a SB301(?) Ham receiver. Only one mistake.
    The instructions for connecting both sides of the IF filter looked the
    same so I skipped one of 'em. Didn't work so well that way.
     
  14. krw

    krw Guest

    It was a crystal, so not much chance of that. ;-)
    Depending on the pins, they're a lot better than many sockets. The
    machined *round* pins were quite good sockets. Of course there were
    sockets (notably from Augat) that used the machined pins, as well.
    Sockets with the stamped square pins were more bother than they were
    worth. I threw out the set that came with a Lear Seigler terminal I
    built and substituted the Augat sockets.
     
  15. Guest

    | wrote:
    |>
    |> | If homes were still fed with DC, the generators would have to be a
    |> | couple miles from your home. Also, it doesn't have to pulse to charge a
    |> | battery.
    |>
    |> If using Edison's 220/110VDC split system, even a couple miles would be way
    |> too far. Today would could do transmission, distribution, service, and
    |> utilization, and different DC voltages and keep it DC all the way. It would
    |> still not be as cheap as AC, but it is possible to do.
    |>
    |>
    | You could do these things but, in practice, it would be a rather stupid
    | step backwards (and somehow involving changes from AC to DC, back to AC
    | etc, ad nauseum. Inefficient and bloody expensive.
    |
    | For distribution, service, utilization, and different DC voltages, there
    | is no comparison, AC wins hands down. With regard to switching, again AC
    | wins. For transmission- it is a balance between line and terminal costs
    | (point to point systems, not grids) or an asynchronous connection is
    | needed- then HVDC has advantages. These factors have been known for
    | roughly 80 years or so. As for generation. DC is severely limited- so
    | what do we do- generate AC (simpler, cheaper and more efficient) step it
    | up or down with simple transformers and then use it in loads that
    | generally don't care whether it is AC or DC or can be handled by an
    | induction motor in a more efficient and far less complex machine than a
    | DC machine.
    |
    | So where to use DC? In those places where it provides a cost or
    | technical advantage or a specific need for DC (long distance HV
    | transmission, long cable systems, asynchronous links between grids,
    | aluminum pot lines, electronic power supplies, etc.)
    | However, for voltage level changing, switching, and most utilization,
    | AC wins. That is a lesson that was learned over 100 years ago and
    | modern electronics hasn't changed the situation. Wishful thinking to
    | the contrary.

    DC went from "you can't do that with DC" to "OK, now you can do that, but why
    would you, since it costs so much" for a lot of things.

    I just can't figure what motivated Edison with DC so much other than trying
    to recoup what he had already invested, and not wanting to admit that he was
    wrong. That, or he though electric lights would be the only use for any
    form of electricity. Motors were around in plenty in those days, so he should
    have seen some alternative uses. I guess he had a comfy box to think in.

    Edison's only hope of more distant power generation (essential when trying to
    exploit renewables like hydro) was some kind of transmission that could drive
    motor-generator sets at local areas. Maybe MVDC (8800/4400V) to drive big
    motors that turn his LVDC (220/110) generators? That would still be quite a
    nightmare to manage (motor genset maintenance vs. transformer maintenance).

    Even I tried to dseign some kind of DC transformer. The best I came up with
    still involved rotating parts (think of a Faraday Homopolar generator with
    an equivalent motor piggybacked). Still a maintenance nightmare compared to
    what AC gets to use.

    OTOH, extremely long electrical transmission is, IMHO, not a good idea, for
    two reasons. It wastes energy (where applicable ... you are stuck if the
    power mover source is a hydro dam, for example, or to get power from wind
    farms where the wind blows the most) in warming the transmission lines. And
    it is an exposure to terrorism. But where we must transmit power, HVDC can
    come out ahead despite its costs when considering not only the losses and
    risks in long distance transmission, but also managing reactive power flow.
    I'm guessing some costs for HVDC will come down, and I hope we do see more
    of HVDC transmission ... for where there is no choice but to do that. But
    I also want to see more localized generation where that is possible. It is
    still a balance. For example, transporting coal from PA/WV/KY to burn in
    localized power plants in the east and northeast would not make sense if that
    transporting is too costly or too exposed to terrorist attack (e.g. taking
    out a major rail bridge may deplete a power plant's 30 day supply, whereas a
    transmission line over the same river could be put back in just a few days).

    BUT ... I still want to call that 240/120 VAC electricity coming into my home
    as TWO phases ... and connect more and more loads to BOTH phases.

    AND ... I want to push for a cabinet full of computer boards/blades powered
    by a big single power supply (one per cabinet) that feeds 12 VDC to each of
    the boards, which is fed by 480 VAC (2 or 3 phases).
     
  16. I don't think that MVDC motors even exist. AFAIK the largest universal motor
    in existence, is the traction motor of an E-Lok, supplied with 700 volts at
    the highest notch (1500 HP, 1 MW)
    The HV induction motors are quite common, they come in 3.3,6.6, 15 and 20 kV
    versions, ranging from 1 MW to ...whatever. One of the largest is the motor
    for the bucket wheel of a brown coal miner, which is supplied directly with
    20 kV.
    I don't think that can even be handled by the commutator and the brushes. Of
    course, the transformator having no moving parts, is a no-brainer....
    Transporting the coal can't beat the efficiency of a well-designed
    trasmission line, which usually is around 99 %.

    --
    Tzortzakakis Dimitrios
    major in electrical engineering
    mechanized infantry reservist
    hordad AT otenet DOT gr
    |
     
  17. Guest

    | I don't think that MVDC motors even exist. AFAIK the largest universal motor
    | in existence, is the traction motor of an E-Lok, supplied with 700 volts at
    | the highest notch (1500 HP, 1 MW)
    | The HV induction motors are quite common, they come in 3.3,6.6, 15 and 20 kV
    | versions, ranging from 1 MW to ...whatever. One of the largest is the motor
    | for the bucket wheel of a brown coal miner, which is supplied directly with
    | 20 kV.

    We haven't needed them, yet.


    | Transporting the coal can't beat the efficiency of a well-designed
    | trasmission line, which usually is around 99 %.

    So then it makes more sense to place the power plant near the coal fields.
     
  18. Don Kelly

    Don Kelly Guest

    ------------
    Look up the Thury system It worked but not really well and died a natural death (oh, those damned
    AC transformers). The mecury arc rectifier was the breakthrough needed
    (about 40 years later in Sweden ), followed by the use of high power
    solid state equipment (initially at Eel River, New Brunswick, Canada).

    As Dimitrious said, MVDC motors weren't available and, generally are
    not available now. High voltage, high current moving contacts
    (commutator) leads to problems that are best avoided. Note that for AC
    machines, the HV side is the stator- very helpful. Sure, 300V,1KA
    commutator generators do exist as exciters for AC machines but I doubt
    whether any of these are built nowadays -as brushless excitation (Fixed
    field, AC 3 phase rotor winding- feeding DC field through a bridge
    mounted on the rotor) is now being used to completely eliminate moving
    contacts.

    With regard to long distance transmission - sure it would be nice for
    all to be local -and since real estate costs would exceed the savings
    involved and not all suitable sources are near the load centers- we are
    stuck with it. The reason for extremely long distance transmission is
    simply that many very desirable sources are also quite distant from load
    centers. There is a relationship between MW-miles and optimal voltage
    levels. In the case of hydro, Quebec's James Bay is a considerable
    distance from NYC and the hydro generation in BC and Washington is also
    quite far away from major load centers. As for coal generation- it has
    always made sense for generation to be near the coal source if at all
    possible- that hasn't changed.
    I think you are overestimating transmission losses as well as terrorist
    activities- Most terrorists aren't stupid enough to target transmission
    lines unless they want minimum bang for their buck.

    By the way, DC transmission doesn't help manage reactive- these systems
    require reactive sources at both ends. What they do is eliminate "line
    reactive" needs and compensation in the form of shunt inductors and
    series capacitors.

    As for your big 12VDC power supply -fine- possibly some gain in
    efficiency (questionable) there is the problem of a high power DC noting
    that each "tap" would have to have breakers capable of handling the full
    fault MW if interruption to all the computers is to be avoided. What
    you might gain from a single base supply is more than made up for by the
    cost /size of appropriate DC breakers.
     

  19. At only 12V it would seem that they would be easier to manufacture than
    the huge HV yards required for HV service protection.

    I mean all they have to do is move a blade between the contacts
    after/as they open,no?
     
  20. Furthermore, nowadays electricity is generated in centralized locations (be
    it coal, hydro or nuclear-nuclear needs generally a large river nearby) or
    oil (mazut) or natural gas, as in the case of Crete. The most common for
    base loads is a steam plant, which runs for 1 1/2 years non stop after it
    has been synchronized. Here, in Crete we have large 2-stroke diesels (mazut
    fired) which run for 6 months, and small stem turbines (for 1 year). The
    grid HV here is 150 kV. In Kozani, where the brown coal veins are, it is
    raised from 21 kV to 400 kV for transmission to Athens and Thessaloniki, the
    main demand centres. I don't know whether terrorists would target the
    transmission lines, but breaker yards are heavily guarded, and extremely
    hazardous if you don't know what you're doing (even 150 kV would immediately
    vaporize a human upon direct contact). In Crete, furthermore, there are
    redundant transmission lines, for safety.
     
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