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280V motor on 230V circuit

Discussion in 'Electronic Repair' started by Deodiaus, Apr 26, 2008.

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  1. It seems they are moving to 400V as well, but I know many Norwegians
    are paying a hefty premium on their three phase equipment, like
    heatpumps.

    My heatpump use an internally star configured 3x400V compressor, and
    it would have been easy to wire it for 3x230V if they had brought out
    all the leads.
     
  2. Guest

    | Professional washing machines. One of my very first days 'in the field' was
    | to connect some of them. They have a large heating element, you can connect
    | it single phase, or 3 phase, it just heats up faster (of course) when you
    | connect it 3 phase. (they have a single phase motor, so it works also in
    | pure 230 V).

    If it has 3 elements rated for 230 volts, with 3 separate connections that
    would be to three separate phase for a three phase feed, and all connected
    to the one phase for a single phase feed, then it should heat up at the same
    speed, while drawing three times the current (not accounting for the motor).

    I don't know why it should heat up faster in three phase, or why you would
    say "of course" about it. I would think it would heat up faster if you took
    it over to London and hooked it up to a 240 volt supply.
     
  3. Guest

    | Since I'm posting from GoogleGroups I can't respond to Phil, but the
    | rest of you can be enlightened.

    Actually, I do see the ones the respond to my own posts. I think the reader
    does that to keep the threading intact. New posts I won't see. And that is
    what most of the spam is (I've seen some spammers that do followups to other
    posts).


    | In 120/240 or similar systems there is not the freedom to choose this
    | ratio. The wiring of the source transformer determines it. As others
    | have noted, in the "Edison" U.S. system the source is a center tapped
    | transformer with the center tap grounded. This makes a two phase
    | system with each 120v "leg" 180 degrees out of phase with the other
    | one. The ratio of the high voltage (240v) and the low voltage (120v)
    | is always therefore 2:1.
    |
    | In a three phase system there will be three transformers with
    | secondaries (one for each phase) wired in a "star" or "Y"
    | configuration. This is necessary because you need the center point of
    | the "star" or "Y" to be ground for each low voltage phase. If you wire
    | with a "delta" configuration there is no central grounding point
    | available for the individual phases. IN three phase circuits the
    | relationship between that individual phases to ground (say 120v) and
    | the voltage measured between phases is not arbitrary. It is always
    | determined by the square root of 3. Hence the between phase voltages
    | being sqrt 3 x 120 = 208V. Just like the two phase system these
    | ratios are determined by physics and can't be arbitrarily set.

    There is no more or less option to choose once you have either system. The
    choice you have is between the systems. If you have single phase, you only
    get 2.0 as a ratio. If you have three phase, you only get 1.7320508 as a
    ratio.


    | Of course there is the issue that electric companies often will name a
    | voltage one thing while actually supplying an other for small
    | variations about the "standard" voltage.

    They call it 208 volts, but it's closer to 207.8460969 :)

    Precise voltage is not really practical. The voltage standard is a target to
    stay near.
     
  4. Guest

    | writes:
    |
    |>
    |> | Residential power in Norway is normally 230V three phase btw, instead
    |> | of 400V three phase. Their 230V outlets are two phase and ground
    |> | instead of one phase, neutral and ground. Their three phase outlets
    |> | therefore are blue instead of red and have four prongs instead of five.
    |>
    |> Is this the system where the voltage is 133 volts relative to ground and 230
    |> volts between phases (and formerly 127 volts relative to ground and 220 volts
    |> between phases)?
    |
    | Yes.
    |
    |>
    |> If they still use that system, then I'm interested in buying a UPS designed
    |> for that. But it is my understanding it is phased out in cities and hard to
    |> find anymore in rural locations.
    |
    | It seems they are moving to 400V as well, but I know many Norwegians
    | are paying a hefty premium on their three phase equipment, like
    | heatpumps.
    |
    | My heatpump use an internally star configured 3x400V compressor, and
    | it would have been easy to wire it for 3x230V if they had brought out
    | all the leads.

    If all 6 leads of the 3 windings are brought out separate, then it can be wired
    in star for 400/230 volt systems, and in delta for 230/133 volt systems. But
    for Europe in general there would be little reason to do that. There is also
    no reason to do that in North America, as we don't have any 360/208 volt systems
    at all.

    If I were in Europe I'd rather than the 400/230 volt system. In North America
    I'd rather have the 480/277 volt system.
     
  5. It would allow the Norwegians to buy less expensive heatpumps from Sweden :)

    It seems like a very simple and cheap thing to do.
     
  6. Don Kelly

    Don Kelly Guest

    ----------------------------
    --------------
    If I read you correctly, you want to use a second secondary (lower power
    rating) which is tapped and put in series with the main secondary. Now once
    you do this, you have in effect a single secondary with taps just as in a
    conventional tapped secondary. Sure the "tapped section" is lower power-
    because it is a lower voltage but it still has to handle the same current.
    Nothing is gained.
    The problem in tap changing is not "power" but the current being switched.

    In either case the voltage driving short circuit current on tap changing is
    that between taps
    Delta V =A(delta n) Delta Z =B(delta n)^2. where delta n is the change in
    turns between taps. The short circuit current on such a change will be
    proportional to 1/(delta n).

    If you want fine control, then you could go to sliding carbon brush as in a
    variac. The first idea of a separate transformer feeding a variac will not
    solve the "too low" voltage problem of the variac because you are still
    dealing with an autotransformer.


    Don Kelly
    remove the X to answer
     
  7. Don Kelly

    Don Kelly Guest

    ----------------------------
    -------------

    Just a bitch that we have dealt with before:

    Phil- please realize that 207.846096....... is meaningless except that it is
    "about 208". 208V is correct to 3 significant figures which is actually
    better than one can assume to be true in practice. If the voltage line to
    neutral is actually 120.V (note the decimal) then we have 3 significant
    digits implying something between 119.5 Vand 120.5.V
    Then all you can truly claim is 208.V
    If it is 120.0V then there is reason to assume 208.0 V but no more decimals
    than that.
    If you have a meter which gives you 120.000000V with less than 1 part in 120
    million error then you can claim 207.846097V for line to line voltage Do
    you have such a meter?

    Engineering and physics students who ignore the principle of "significant
    digits" lose marks for this "decimal inflation".

    Sure- you can let the calculator carry the extra digits (as it will do
    internally) but accepting these as gospel truth to the limit of the
    calculator or computer display is simply not on as you can't get better
    accuracy from a calculation than the accuracy of the original data (actually
    you will lose a bit). All that you get rid of is round off errors in
    calculations.

    Since, as you say, precise voltage is not really practical, then
    multi-decimal point numbers are meaningless. If we say 120V +/-10% then we
    are talking about 108-132V which for line to line becomes 187-229V (average
    208V) and any extra decimal points don't mean anything.

    Don Kelly
    remove the X to answer
     
  8. Don Kelly

    Don Kelly Guest

    ----------------------------
    ------------
    So you have a differential voltage producing a circulating current through
    both windings leading to losses and heating due to circulating currents. In
    addition, there would be shifts in the load sharing between the two
    secondaries- with the possibility of overloading one of them. Also, you
    still haven't solved the problem of switching the current from one tap to
    another Note also to shift 2% you would have to make two 2% shifts, one on
    each winding so that you are essentially doubling the work and tap changing
    equipment while introducing other problems as Daestrom has indicated.
    -
     
  9. Guest

    | If I read you correctly, you want to use a second secondary (lower power
    | rating) which is tapped and put in series with the main secondary. Now once
    | you do this, you have in effect a single secondary with taps just as in a
    | conventional tapped secondary. Sure the "tapped section" is lower power-
    | because it is a lower voltage but it still has to handle the same current.
    | Nothing is gained.
    | The problem in tap changing is not "power" but the current being switched.

    No, that is not what I tried to explain. I'll try again:

    The main transformer would have 2 secondaries. These 2 secondaries are NOT
    wired in series with each other. The smaller of these secondaries will have
    taps. The tapped smaller secondary feeds another smaller transformer. The
    larger secondary of the main transformer, and the only secondary of the smaller
    auxiliary transformer, would be wired in series. So the taps are only dealing
    with the current of the lower power "tapping section". The smaller secondary
    of the main transformer, and the primary of the auxiliary transformer, can be
    wired for whatever voltage/current works out best.


    | In either case the voltage driving short circuit current on tap changing is
    | that between taps
    | Delta V =A(delta n) Delta Z =B(delta n)^2. where delta n is the change in
    | turns between taps. The short circuit current on such a change will be
    | proportional to 1/(delta n).
    |
    | If you want fine control, then you could go to sliding carbon brush as in a
    | variac. The first idea of a separate transformer feeding a variac will not
    | solve the "too low" voltage problem of the variac because you are still
    | dealing with an autotransformer.

    In that first scheme, adjusting the variac to the lowest voltage would be
    reducing the voltage contributed by the boost transformer. There is still
    the original supply voltage going around the variac, "plus" (actually minus)
    the buck voltage (to select the range I want). Since the variac is an
    autotransformer itself, it merely feeds the primary of the boost transformer.
    Note that in this case the "boost" transformer is wired as an isolation
    transformer. I should have mentioned that. If needed, I guess I could draw
    some ASCII diagrams or try to get something made graphically (all the tools
    I have to do that suck, except for Visio which needs Windows to run and I
    don't have a spare machine to do that at the moment).
     
  10. Guest

    |
    | |>
    |> | Yes -you are shorting a part of the winding but the switching is a bit
    |> more
    |> | complex than that so that short circuit currents are limited to
    |> reasonable
    |> | values. It is a multistep operation with reactor switching. On-load tap
    |> | changers are expensive and are generally limited to applications where
    |> this
    |> | is absolutely needed (I have seen one where the tap changer was nearly
    |> as
    |> | large as the transformer).
    |>
    |> What about multiple parallel transformers, or at least multiple parallel
    |> windings on the same core (on whichever side the tapping is to be done),
    |> where the taps are stepped incrementally on each winding? Instead of a
    |> shorted winding segment, you'd have windings of differing voltage in
    |> parallel as each of the windings change their taps one at a time.
    |>
    |
    | So when one is set for say 118V and the other is set for 120V, you have a
    | 118V source connected in parallel with a 120V source and the only impedance
    | is the transformer windings??
    |
    | OUCH!!! I think the magic smoke will be spewing in no time

    I was afraid of that.

    That also means if you are going to parallel 2 transformers, they better have
    exactly the same winding ratio.
     
  11. Guest

    | Phil, did you see daestrom's excellent explanation how they use an
    | inductor to prevent a dead short but in a way such that the inductor is
    | virtually not there during normal operation (counterflowing currents)?

    I believe I missed that.


    | If these tap changers are rather expensive, I'm wondering what those
    | pole pig "voltage regulators" I mentioned are. I thought they were just
    | tapped autotransformers.

    Sounds like they may be more of a voltage selector.

    One set of transformers I saw once had a voltage selector which also revealed
    the voltage to me. Even those these huge things were well guarded behind a
    chainlink fence with barbed wire on top, I could clearly read the instructions
    on the voltage taps. It listed 5 or 6 different voltages in the 4160 volt
    range (I believe that was a middle one). The secondaries were a thick bundle
    of insulated wires not on insulator standoffs, so obviously LV, possibly 480V
    or 208V. These were 3 single tank transformers in roughly the design style
    of a pole pig (round tank) with a control panel on them with the tap control
    and some gauge I guessed may be temperature (but I could not see it clear
    enough at the distance I was at to be sure). The instructions did indicate
    that the transformer must be de-energized (not just unloaded) when making the
    change. So I'm guessing they were just to compensate for variations in the
    delivered voltage. These transformers were about 1 meter wide and 2.5 meters
    high, each (3 of them). I did not see any reference to a kVA rating. They
    were also very old looking (pre-WWII). They were humming.
     
  12. Guest

    | Just a bitch that we have dealt with before:
    |
    | Phil- please realize that 207.846096....... is meaningless except that it is
    | "about 208". 208V is correct to 3 significant figures which is actually
    | better than one can assume to be true in practice. If the voltage line to
    | neutral is actually 120.V (note the decimal) then we have 3 significant
    | digits implying something between 119.5 Vand 120.5.V
    | Then all you can truly claim is 208.V
    | If it is 120.0V then there is reason to assume 208.0 V but no more decimals
    | than that.
    | If you have a meter which gives you 120.000000V with less than 1 part in 120
    | million error then you can claim 207.846097V for line to line voltage Do
    | you have such a meter?
    |
    | Engineering and physics students who ignore the principle of "significant
    | digits" lose marks for this "decimal inflation".
    |
    | Sure- you can let the calculator carry the extra digits (as it will do
    | internally) but accepting these as gospel truth to the limit of the
    | calculator or computer display is simply not on as you can't get better
    | accuracy from a calculation than the accuracy of the original data (actually
    | you will lose a bit). All that you get rid of is round off errors in
    | calculations.
    |
    | Since, as you say, precise voltage is not really practical, then
    | multi-decimal point numbers are meaningless. If we say 120V +/-10% then we
    | are talking about 108-132V which for line to line becomes 187-229V (average
    | 208V) and any extra decimal points don't mean anything.

    You didn't notice the :) I put on the number?

    We've been over this. I know the practice of significant digits, and how
    the voltages are designated (two different reasons you can get 208). I do
    follow the practice of carrying exactly the result of calculations into
    other calculations. I also use over significance in comparison of numbers.

    But I also know that rounding is a form of noise. So I avoid it until the
    time I end up with the final result. So if I multiply 120 by the square
    root of three I do get a number like 207.84609690826527522329356 which is
    either carried as-is into the next calculation, or rounded if it is the
    final answer. If some other strange calculation happens to give me the
    value 207.84609690826527522329356 then I know it is effectively equivalent
    to 120 times the square root of three in some way. But if what I get is
    208.455732193971783228 then I know it has nothing to do with 120 times the
    square root of three, even though it, too, would end up as 208 if rounded
    to 3 significant digits.

    When it comes to _measured_ amounts, as opposed to synthetic ones, then the
    significance rules dictate how to round the results. With synthetic numbers
    (e.g. numbers I can just pick), I can also pick the rounding rules for the
    final results. But if I don't know that the calculations are done (e.g. I
    am not merely giving a designation for a voltage system), where someone else
    may take those numbers and do more calculations and round the results, then
    I do use more significance. But that is no different to me than just carrying
    that number from one calculation stage to another.
     
  13. Guest

    | writes:
    |
    |> | writes:
    |> |
    |> |>
    |> |> | Residential power in Norway is normally 230V three phase btw, instead
    |> |> | of 400V three phase. Their 230V outlets are two phase and ground
    |> |> | instead of one phase, neutral and ground. Their three phase outlets
    |> |> | therefore are blue instead of red and have four prongs instead of five.
    |> |>
    |> |> Is this the system where the voltage is 133 volts relative to ground and 230
    |> |> volts between phases (and formerly 127 volts relative to ground and 220 volts
    |> |> between phases)?
    |> |
    |> | Yes.
    |> |
    |> |>
    |> |> If they still use that system, then I'm interested in buying a UPS designed
    |> |> for that. But it is my understanding it is phased out in cities and hard to
    |> |> find anymore in rural locations.
    |> |
    |> | It seems they are moving to 400V as well, but I know many Norwegians
    |> | are paying a hefty premium on their three phase equipment, like
    |> | heatpumps.
    |> |
    |> | My heatpump use an internally star configured 3x400V compressor, and
    |> | it would have been easy to wire it for 3x230V if they had brought out
    |> | all the leads.
    |>
    |> If all 6 leads of the 3 windings are brought out separate, then it can be wired
    |> in star for 400/230 volt systems, and in delta for 230/133 volt systems. But
    |> for Europe in general there would be little reason to do that. There is also
    |> no reason to do that in North America, as we don't have any 360/208 volt systems
    |> at all.
    |
    | It would allow the Norwegians to buy less expensive heatpumps from Sweden :)
    |
    | It seems like a very simple and cheap thing to do.

    My guess is that in the cities, they have already changed over to a 400/230
    system, or at least a 380/220 system that hasn't been voltage adjusted, yet.
    What I've heard is the 220/127 system was a leftover in some rural areas of
    Norway, and also in Spain. Apparently Suadi Arabia has this system so they
    can make use of both European and American single phase appliances. Mexico
    also has 220/127 but primarily uses the 127 volt connection (and it's 60 Hz).
    The really strange thing is Brazil has 220 volts all around the country,
    with 60 Hz in some parts and 50 Hz in others, and used to use the American
    120 volt 2-blade outlet/plug with 220 volts (you can be in for a surprise
    with that).
     

  14. All distribution transformers, sometimes called "pole pigs", that I
    have seen had some sort of voltage adjusting system, usually referred
    to as taps. Usually they are an actual bolted "tap" and you open the
    transformer and set the output voltage by making the proper tap
    connection when the transformer is installed and frankly it is usually
    ignored thereafter.

    The other "cans" you often see on poles are capacitors used to adjust
    the power factor on some secondaries.

    Bruce-in-Bangkok
    (correct Address is bpaige125atgmaildotcom)
     
  15. Yes, because as the germans say-"Sie nehmen Strom direct aus der
    Leitung"-They draw power directly from the wire. So it's a higher impulse
    current than any on board diesel can provide;_)
    Of course you are, but I thought there might be other members of the group,
    that don't. I didn't know until I read the article. The large, 15,000 HP, 11
    MW diesels we have here at our local power station, have a final steam
    stage, for better efficiency. The URL of our local college, where I got my
    degree, is www.teiher.gr , but I'm not sure if they got an english version.
    In Germany, they have special locomotives for freight trains, and special
    for passenger ones. The former desingned for larger traction power, the
    latter for higher speed. I have more experience with ships, since there are
    no railroads in Crete, but there's a lot of sea, and islands in Greece:)
    I'll never forget my trip to Rhodes, where my batallion was situated, by
    rail from Korinthos (the infamous boot camp) and with ship to Rhodes. She
    was full of soldiers and commuters:)
    NB.:There are railroads in continental Greece.


    --
    Tzortzakakis Dimitrios
    major in electrical engineering
    mechanized infantry reservist
    hordad AT otenet DOT gr
    NB:I killfile googlegroups.
     
  16. Or disconnect switches, plain or with high-voltage fuses.
    --
    Tzortzakakis Dimitrios
    major in electrical engineering
    mechanized infantry reservist
    hordad AT otenet DOT gr
    NB:I killfile googlegroups.
     
  17. Maybe you connected with single phase just one element? The rest two
    remained unconnected? (3 230 volts elements, connected wye). I'm sure it
    heated up faster, in 3 phase connection.





    --
    Tzortzakakis Dimitrios
    major in electrical engineering
    mechanized infantry reservist
    hordad AT otenet DOT gr
    NB:I killfile googlegroups.
     
  18. There should be no problem with the frequency, the local US base (In
    Gournes-decomissioned after the end of the Cold War) used a regular 15 kV,
    50 Hz feed, from the cretan grid, which was stepped down to 4150 volts and
    then to 120/240. All with US switchgear and tranformers! (NB for US guys.#10
    wire gauge->10 mm2 main feed of residence, #12 ->6 mm2 stove,#14->4 mm2
    water heaters, #16->2.5 mm2 washing machines, dryers, #18->1.5 mm2
    lighting.-approximately). I think that the personnel of the base used
    standard US fluorescent light fixtures and other equipment, sone of it was
    left as some of the buildings "inherited" by the greek state, were converted
    by us to 230/400 volts, with regular Schuko receptacles.


    --
    Tzortzakakis Dimitrios
    major in electrical engineering
    mechanized infantry reservist
    hordad AT otenet DOT gr
    NB:I killfile googlegroups.
     
  19. Guest

    | ? <> ?????? ??? ??????
    | |> In alt.engineering.electrical Tzortzakakis Dimitrios <>
    |> wrote:
    |>
    |> | Professional washing machines. One of my very first days 'in the field'
    |> was
    |> | to connect some of them. They have a large heating element, you can
    |> connect
    |> | it single phase, or 3 phase, it just heats up faster (of course) when
    |> you
    |> | connect it 3 phase. (they have a single phase motor, so it works also in
    |> | pure 230 V).
    |>
    |> If it has 3 elements rated for 230 volts, with 3 separate connections that
    |> would be to three separate phase for a three phase feed, and all connected
    |> to the one phase for a single phase feed, then it should heat up at the
    |> same
    |> speed, while drawing three times the current (not accounting for the
    |> motor).
    |>
    |> I don't know why it should heat up faster in three phase, or why you would
    |> say "of course" about it. I would think it would heat up faster if you
    |> took
    |> it over to London and hooked it up to a 240 volt supply.
    |>
    | Maybe you connected with single phase just one element? The rest two
    | remained unconnected? (3 230 volts elements, connected wye). I'm sure it
    | heated up faster, in 3 phase connection.

    You were the one who said "it just heats up faster (of course) when you
    connect it 3 phase."

    I would disagree.

    But the fact that you said "(of course)" seems you presume that to be the
    general case. Now your most recent comment at least acknowledges that if
    not all elements are connected, it won't heat up as fast.

    In the simple case, each of 3 elements is individually wired, so you have
    a total of 6 leads. When connecting to three phase, one lead of each is
    connected to neutral, and each of the other leads is connected to separate
    phases. When connecting to single phase, they are all wired in parallel.
    Both cases always involve one of the leads from each element connected to
    neutral, so those 3 leads can be pre-connected together. So you could have
    just 4 leads. The common neutral lead needs to be rated for all the current
    together for it to be rated properly for single phase.

    It should apply the same voltage (230V) to each element, and they should each
    draw the same current. How would you believe this would be slower to heat?

    If the 3 elements were wired _internally_ in star without a neutral lead,
    it would still work fine on three phase as long as all elements were equal
    impedance. But on single phase, you could only activate 2 of the elements,
    and that would be 2 in series fed with 230 volts. You'd only get 1/6 the
    power that way.

    Are you assuming the elements would be wired that way? That would clearly
    NOT be intended for single phase connection.

    The 3 elements could be wired _internally_ in delta. In this case, these
    would have to be 400V elements. Connecting 2 leads to 230 volts would still
    give you only 1/6 the power (but more evenly distributed in this case).

    So what is the situation that makes _you_ believe that 3 elements connected
    to single phase _will_ draw less power to heat the water than when connected
    to three phase?
     
  20. Don Kelly

    Don Kelly Guest

    ---------------------------------
    Actually I see added complexity without any gain. You may be doing the tap
    changing at a lower current and higher voltage but there will be no "lower
    Power" switching but there will be more losses during operation even when
    not changing taps. I suspect the complexity and the losses together would
    cost more than a conventional tap changer. There are some circuit factors
    involved which may be undesirable but I haven't done a proper analysis.[/QUOTE]
     
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