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280V motor on 230V circuit

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

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  1. James Sweet

    James Sweet Guest


    Regardless, the regulation is very good. I monitored mine for a while
    and never saw it dip below 118V or go above 122V, most of the time it
    was just about spot on 120V. A friend in the UK was doing the same on
    his and it went as low as 224V and as high as 246V. We've done a lot of
    comparing and have agreed that neither system is inherently better or
    worse than the other, both have advantages and disadvantages.
     
  2. charles

    charles Guest

    or, as in the case of the transformer that feeds my house, pole mounted in
    field with the output cables going underground immediately.
     
  3. Guest

    | In article <[email protected]>,
    |>
    |> It's not 110V, it's 240V, we simply split it with a grounded center tap
    |> which gives 120V between each side and neutral, or 240V between the sides..
    |
    | It's the regulation at 120V which people notice.
    | If you want to call it a 240V supply, then you
    | need to call EU supplies 400V or 415V. That's
    | equally misleading.

    The effect of loading and how it affects voltage depends on how well balanced
    the TWO 120 volts phases are. If they are in balance, then the effect of the
    loading on the voltage works as if you were considering the voltage at 240 volts.

    If you get a three phase supply, and keep it balanced with the single phase
    line to neutral loads, then the voltage regulation is going to be just like you
    had loaded it with line-to-line loads, 208 volts in North America and 400 volts
    in Europe.

    If your neighborhood transformer is three phase, even if your home gets only
    one phase of it (at just 230 volts), you still get advantage because other
    homes will be distributed over other phases to keep it in balance.

    But if you are comparing a single phase system, North American 120/240 with
    three wires, vs. European 230 with two wires, it works out to be about the
    same. The difference is we pay more for the extra wire, but we have a lower
    line to ground shock risk (which isn't really much of an issue anymore with
    improvements in safety in various ways such as GFI/RCD protection, better
    rules on installations, etc).

    So if you moved from Europe where you had 400/230 volts three phase in your
    home, and came to North American and discovered we really had 480/277 volts
    three phase, would that trouble you (assuming all appliances were designed
    for that)?
     
  4. The regulation, at least in Europe, is done at 150/15 kV substations and at
    the HV side of the transformers, thus at 150 kV. Typical current for 2 x 25
    MVA transformers is 150 A, 150 kV and of course secondary at 15 kV, 1500 A.
    The regulation is done automatically with tap changers, live. The local
    transformers at your neighborhood are fixed tap, 15 kV (they intend to
    change everything to 20 kV).
     
  5. I'm referring to the transformer regulation (and also the LV
    supply cable voltage drop) response to load changes. E.g. if
    I switch on my 10kW shower, that's a 0.1% change against the
    max load of my 1MVA substation transformer and therefore
    makes no perceivable difference to the voltage in my house.
    If I were to try that on a US 50kVA transformer, that load
    is going to trigger a change of 20% of the transformer
    regulation, which is much more significant and would
    certainly be visible as a brightness change in light bulbs.

    Having lived in both countries, I would say it's pretty much
    expected in the US that lights dim even with quite moderate
    loads coming on, whereas it's rare in the UK (generally only
    in rural areas with long supply lines). There are many
    contributory factors to this difference, but the 120V verses
    240V (or if you must, 240V verses 415V) is ultimately the
    underpinning reason.

    Automatic tap changing in the HV network is completely
    invisible to the residential consumer, as indeed it should
    be.
     
  6. Guest

    | I'm referring to the transformer regulation (and also the LV
    | supply cable voltage drop) response to load changes. E.g. if
    | I switch on my 10kW shower, that's a 0.1% change against the
    | max load of my 1MVA substation transformer and therefore
    | makes no perceivable difference to the voltage in my house.
    | If I were to try that on a US 50kVA transformer, that load
    | is going to trigger a change of 20% of the transformer
    | regulation, which is much more significant and would
    | certainly be visible as a brightness change in light bulbs.

    What is the available fault current in these situations?
     
  7. James Sweet

    James Sweet Guest

    Mine dim slightly for an instant when my 3 ton heat pump kicks in, it's
    only noticeable with the few incandescent lights left in the house
    though. The LRA on that thing is something like 90A. I think most of the
    drop must be in the 50' or so of 2/0 AL wire between the meter base and
    the transformer though as they don't seem to dim at all from any of the
    neighbors.
     
  8. You

    You Guest

    Yep, their called Super Conducting Transformers, and they have been
    around the LABS, for about 15 years now. Only one BIG problem with them.
    They only work at 20 Degrees Kevin or lower in temperature.
     
  9. Guest

    | The central air kicks on without my lights dimming, and I am in North
    | Central Florica.

    I bet it's on its own branch circuit, too.
     
  10. James Sweet

    James Sweet Guest


    Of course it is, that's the only legal way to do it.
     
  11. Guest

    | wrote:
    |>
    |>
    |> | The central air kicks on without my lights dimming, and I am in North
    |> | Central Florica.
    |>
    |> I bet it's on its own branch circuit, too.
    |
    |
    | So what? The meter is on a pole on one side of the driveway ( two
    | feet from the property line, because Progress Energy does not allow
    | drops to cross a driveway anymore.), and an outdoor breaker box is on
    | the remaining four foot stump of the old pole on the other side of the
    | paved drive, about 40 feet away. The 60 A breaker for the AC is in that
    | box, along with the 100 A main breaker that is used as a disconnect for
    | the house. That box is over 125 feet from the pole pig, on a 150 A
    | service. That box also feeds another underground line to the laundry
    | building,, and well pump. The main breaker box for the house is another
    | 20 feet from the outdoor box. Now, tell me how it can have no effect on
    | the line voltage. I still see very little flickering, usually only on
    | hot summer days when everyone in the subdivision is using the AC and
    | their kitchen stoves at the same time. That is usually followed by a
    | blown 60 A fuse in the 7200 volt line, feeding my street.

    If it were not on its own branch circuit, that would (in addition to being
    a code violation) more likely cause other stuff (whatever else is on the
    same circuit) to experience dimming. The fact that it is onis own branch
    circuit doesn't mean there isn't a big voltage drop. But only the A/C would
    be getting it, and it wouldn't matter (much).

    It can have no (or very little that cannot be noticed) effect on the line
    voltage because you have good wiring and the transformer has a high enough
    capacity and low enough impedance. This is stuff you know.

    Blowing a 60 amp fuse at 7200 volts is not a small neighborhood.

    I can understand them not wanting to go overheard over a driveway. RVs can
    be a fun place for kids to climb on (even if terribly unsafe). Or they can
    catch fire (I've seen that happen and it _was_ a case of a service drop over
    a driveway that faulted when the insulation melted off).
     
  12. Guest

    | wrote:
    |>
    |> | wrote:
    |> |>
    |> |>
    |> |> | The central air kicks on without my lights dimming, and I am in North
    |> |> | Central Florica.
    |> |>
    |> |> I bet it's on its own branch circuit, too.
    |> |
    |> |
    |> | So what? The meter is on a pole on one side of the driveway ( two
    |> | feet from the property line, because Progress Energy does not allow
    |> | drops to cross a driveway anymore.), and an outdoor breaker box is on
    |> | the remaining four foot stump of the old pole on the other side of the
    |> | paved drive, about 40 feet away. The 60 A breaker for the AC is in that
    |> | box, along with the 100 A main breaker that is used as a disconnect for
    |> | the house. That box is over 125 feet from the pole pig, on a 150 A
    |> | service. That box also feeds another underground line to the laundry
    |> | building,, and well pump. The main breaker box for the house is another
    |> | 20 feet from the outdoor box. Now, tell me how it can have no effect on
    |> | the line voltage. I still see very little flickering, usually only on
    |> | hot summer days when everyone in the subdivision is using the AC and
    |> | their kitchen stoves at the same time. That is usually followed by a
    |> | blown 60 A fuse in the 7200 volt line, feeding my street.
    |>
    |> If it were not on its own branch circuit, that would (in addition to being
    |> a code violation) more likely cause other stuff (whatever else is on the
    |> same circuit) to experience dimming. The fact that it is onis own branch
    |> circuit doesn't mean there isn't a big voltage drop. But only the A/C would
    |> be getting it, and it wouldn't matter (much).
    |>
    |> It can have no (or very little that cannot be noticed) effect on the line
    |> voltage because you have good wiring and the transformer has a high enough
    |> capacity and low enough impedance. This is stuff you know.
    |>
    |> Blowing a 60 amp fuse at 7200 volts is not a small neighborhood.
    |
    |
    | 48 lots, 47 with homes. That gives 7200*60/240 or 1800 A @ 240 V for
    | 47 homes gives an average 38.29 A per home which is the reason that fuse
    | can blow more than once a week, along with it's explosive discharge that
    | sounds like a shotgun every time it blows.

    Yup, big neighborhood. It wouldn't take much after 47 home central A/C's
    are running to go over the fuse rating. Any guess what the curve on that
    fuse is? E.g. how long can you go at 105%? 125%?
     
  13. Of course not:) These are approximate figures (like the 21 kV 10 kA
    alternator, which in fact is 9823 A 21200 volts or whatever). But the
    efficiency of large transformers or transmission lines, when they operate at
    optimum is 99%.
     
  14. I know that, but it was a temptation to post this:)
    A shame that Tesla won the infamous "battle" and we don't have DC:-() But
    then, we would be having a power plant at each neighborhood, instead of the
    300 MW ones.
    We have here capacitor banks, too, connected at the LV side of the
    substation, 15 kV line-to-line voltage.
    But just like in
    Yeah, the ones we have here are automatic, live and even have a shaft for
    manual control.I know, I know, my answer was a bit provocative:) And of course there are
    DC regulators.... You're talking about DC generators;the one a 300 MW uses
    for excitation is 220 V, 1000 A DC and probably shunt field. I have seen
    here in some machine shops the old type welding generator, which is a 3
    phase induction motor coupled to (usually) a compound field DC generator,
    which provides the welding current. The modern ones are, maybe, not larger
    than a shoe box and powered by a higher wattage 230 V 16 A receptacle.
    (Usual receptacles are 230 V 10 A;16 A for washing machines, dryers and the
    like).
     
  15. Guest

    | A shame that Tesla won the infamous "battle" and we don't have DC:-() But
    | then, we would be having a power plant at each neighborhood, instead of the
    | 300 MW ones.

    And the latter make easy terrorism targets, too.


    | I know, I know, my answer was a bit provocative:) And of course there are
    | DC regulators.... You're talking about DC generators;the one a 300 MW uses
    | for excitation is 220 V, 1000 A DC and probably shunt field. I have seen
    | here in some machine shops the old type welding generator, which is a 3
    | phase induction motor coupled to (usually) a compound field DC generator,
    | which provides the welding current. The modern ones are, maybe, not larger
    | than a shoe box and powered by a higher wattage 230 V 16 A receptacle.
    | (Usual receptacles are 230 V 10 A;16 A for washing machines, dryers and the
    | like).

    You don't use 400 V for anything heavy duty like an oven?
     
  16. And so does that 20 gallons of gasoline parked
    in front of your house. And that 500 gallons
    of diesel fuel in your basment. And that 20,000
    or so gallons in the nearby gas station.

    Yawn.
     
  17. Guest

    | Are the load tap generators configured make-before-break?
    | Break-before-make would mean a (very short) power outage every activation
    | but make-before-break would mean a momentarily short-circuited winding and
    | the break would involve interrupting a large short circuit current.

    I wonder how much regulation could be managed through the use of variable
    leakage inductance in the transformer windings.


    | Certainly modern ones likely use thyristors and zero crossing detectors.

    With zero crossing detection, then the switching is not happening on all phases
    at the same time.
     
  18. James Sweet

    James Sweet Guest


    In North America, 240V 50A is pretty standard for ovens, some are 40A,
    clothes dryers are 30A, most other stuff plugs into a 15A 120V receptacle.
     
  19. Some parts of Europe do. You find ovens can be strapped to
    run from one or two phases, depending what's available on
    the premises. Some parts of Europe use 3-phase 400V domestic
    water heaters.
     
  20. Guest

    Continental Europe used to have 220 volts (before that it was 127 volts in
    some places), the UK used to have 240 volts. Nowadays, the common voltage
    is 230 volts -10% +6%.
     
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